Ci a ion: Rakshi , S.; Medina, A.M.;
Lezama, L.; Cohen, B.; Douhal, A.
The E ec s o Mono- and Bi alen
Linea Alkyl In e laye Space s on
he Pho obeha io o Mn(II)-Based
Pe o ski es. In . J. Mol. Sci. 2023,24,
3280. h ps://doi.o g/10.3390/
ijms24043280
Academic Edi o : Giuseppe Zano i
Recei ed: 14 Janua y 2023
Re ised: 1 Feb ua y 2023
Accep ed: 2 Feb ua y 2023
Published: 7 Feb ua y 2023
Copy igh : © 2023 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
In e na ional Jou nal o
Molecula Sciences
A icle
The E ec s o Mono- and Bi alen Linea Alkyl In e laye
Space s on he Pho obeha io o Mn(II)-Based Pe o ski es
Soumyadip a Rakshi 1,†, Alicia Maldonado Medina 1,† , Luis Lezama 2, Boiko Cohen 1,*
and Abde azzak Douhal 1,*
1Depa amen o de Química Física, Facul ad de Ciencias Ambien ales y Bioquímica and INAMOL,
Uni e sidad de Cas illa-La Mancha, 45071 Toledo, Spain
2Depa amen o de Química O gánica e Ino gánica, Facul ad de Ciencia y Tecnología, Uni e sidad del País
Vasco, UPV/EHU, Bº Sa iena s/n, 48940 Leioa, Spain
*Co espondence: [email p o ec ed] (B.C.); [email p o ec ed] (A.D.)
† These au ho s con ibu ed equally o his wo k.
Abs ac :
Mn(II)-based pe o ski e ma e ials a e being in ensi ely explo ed o ligh ing applica ions;
unde s anding he ole o ligands ega ding hei pho obeha io is undamen al o hei de elopmen .
He ein, we epo on wo Mn (II) b omide pe o ski es using mono alen (pe o ski e 1, P1) and
bi alen (pe o ski e 2, P2) alkyl in e laye space s. The pe o ski es we e cha ac e ized wi h powde
X- ay di ac ion (PXRD), elec on spin pa amagne ic esonance (EPR), s eady-s a e, and ime- esol ed
emission spec oscopy. The EPR expe imen s sugges oc ahed al coo dina ion in P1 and e ahed al
coo dina ion o P2, while he PXRD esul s demons a e he p esence o a hyd a ed phase in P2
when exposed o ambien condi ions. P1 exhibi s an o ange- ed emission, while P2 shows a g een
pho oluminescence, as a esul o he di e en ypes o coo dina ion o Mn(II) ions. Fu he mo e, he
P2 pho oluminescence quan um yield (26%) is signi ican ly highe han ha o P1 (3.6 %), which we
explain in e ms o di e en elec on-phonon couplings and Mn-Mn in e ac ions. The encapsula ion
o bo h pe o ski es in o a PMMA ilm la gely inc eases hei s abili y agains mois u e, being mo e
han 1000 h o P2. Upon inc easing he empe a u e, he emission in ensi y o bo h pe o ski es
dec eases wi hou a signi ican shi in he emission spec um, which is explained in e ms o an
inc ease in he elec on-phonon in e ac ions. The pho oluminescence decays i wo componen s
in he mic osecond egime— he sho es li e ime o hyd a ed phases and he longes one o non-
hyd a ed phases. Ou indings p o ide insigh s in o he e ec s o linea mono- and bi alen o ganic
in e laye space ca ions on he pho ophysics o hese kinds o Mn (II)-based pe o ski es. The esul s
will help in be e designs o Mn(II)-pe o ski es, o inc ease hei ligh ing pe o mance.
Keywo ds:
pho oluminescence; Mn (II); pe o ski e; oc ahed on; e ahed on; LED; quan um yield;
li e ime; elec on-phonon coupling; Mn-Mn in e ac ions
1. In oduc ion
Resea che s ha e known abou pe o ski es (PSs) since he la e 19 h cen u y; howe e ,
i was only a e he pionee ing wo k by Miyasaka and co-wo ke s [
1
] ha o ganic-ino ganic
pe o ski es ecei ed ex ao dina y a en ion, owing o hei emendous success in pho o-
ol aic and ela ed op oelec onic de ices. One o he in e es ing ea u es o hese s uc u es
is hei abili y o accommoda e la ge ca ions, which pa es he way o small o ganic ca ions
o pa icipa e in hei amewo k, leading o o ganic-ino ganic hyb idiza ion [
2
,
3
]. Du ing
he las i e yea s, hyb id o ganic-ino ganic PS-based sola cells and LEDs ha e expe ienced
ema kable and unp eceden ed achie emen s [4–9].
Despi e eaching impo an miles ones in a sho ime, lead (Pb)-based pe o ski es
su e om unsa is ac o y long- e m s abili y due o mobile ionic ea u es, and oxici y,
which in u n educe he possibili y o hei comme cializa ion. The e o e, i is desi able
In . J. Mol. Sci. 2023,24, 3280. h ps://doi.o g/10.3390/ijms24043280 h ps://www.mdpi.com/jou nal/ijms
In . J. Mol. Sci. 2023,24, 3280 2 o 16
o de elop Pb- ee s able and highly luminescen o ganic-ino ganic hyb id pe o ski es
wi h la ge s abili y and excellen pe o mance. To his end, a se ies o en i onmen ally
iendly al e na i es, such as in (Sn
2+
), coppe (Cu
2+
), bismu h (Bi
3+
), and an imony (Sb
3+
)
ca ions ha e been explo ed o eplace he oxic Pb
2+
. Among hese al e na i es, Sn-based
pe o ski es showed g ea po en ial, bu un o una ely, he apid oxida ions o Sn
2+
and
Sn
4+
d as ically hinde hei s abili y and, hence, hei applicabili y [
10
–
12
]. Howe e ,
o 2D Sn-based Ruddlesden-Poppe pe o ski es, he sizes and con igu a ions o o ganic
space ca ions ha e ema kable e ec s on he p ope ies o hese ma e ials [13,14].
Many esea che s ha e u ned hei a en ion o Mn (II)-based o ganic-ino ganic hy-
b id pe o ski es as al e na i e ligh emi e s owing o hei nonlinea op ical p ope ies
and unable luminescence [
15
–
19
]. Mul i e oics and phase-change memo ies a e also
obse ed in hese ma e ials [
20
–
24
], as well as he coexis ence o mul iple pe o mances.
The emissions o hese pe o ski es depend on he coo dina ion en i onmen o Mn
2+
e-
sul ing om he
4
T
1
-
6
A
1
ansi ion [
15
,
25
,
26
]. I has been es ablished ha oc ahed ally
coo dina ed Mn
2+
ca ions show o ange o ed emissions, whe eas e ahed ally coo -
dina ed ones exhibi g een pho oluminescence. G een emissions a e ins iga ed by wo
majo ac o s: (i) he absence o an in e sion cen e in he e ahed al en i onmen and
(ii) inc eased elec ic-dipole oscilla o s eng h due o he small c ys al ield spli ing ene gy
o [MnX
4
]
2−
. In he oc ahed al en i onmen , he ed emission is associa ed wi h a highe
Mn-Mn coupling in e ac ion esul ing om sho Mn-Mn dis ances (3–5 Å) [
27
,
28
]. Apa
om he single g een o ed emission bands, dual emission has also been epo ed in a ew
cases due o he coexis ence o bo h en i onmen s and/o om elec on-phonon coupling
a ia ion [
29
–
31
]. T iboluminescence is ano he in e es ing phenomenon ha has been
obse ed in non-cen osymme ic c ys als o Mn (II) complexes owing o i s g ea po en ial
in s uc u al damage sensing, s ess sensing, display, and secu i y ma king [32–35].
Subs i u ion o halide ions and changing he o ganic coun e ions a e also e ec-
i e in modula ing he op ical and physical p ope ies o hese ma e ials. Fo example,
(py olidinium)MnCl
3
and (py idine)MnCl
3
oc ahed al coo dina ion we e epo ed o
exhibi ed/o ange emissions while hei b omide coun e pa s (py olidinium)
2
MnB
4
and (py idine)
2
MnB
4
we e ound o emi in he g een egion due o hei e ahed al
coo dina ion [
15
,
36
]. Two pe o ski es, (C
5
H
6
N)
2
MnB
4
and (C
5
H
6
N)MnB
3
—wi h di e -
en c ys al s uc u es—ha e been syn hesized by adjus ing he amoun o he py idinium
ca ion. The i s one has an isola ed mononuclea s uc u e wi h a e ahed on [MnB
4
]
2−
uni , and he second one has a linea chain wi h an oc ahed al [MnB
6
]
4−
pa o gi e
g een and ed emission bands, espec i ely [
17
]. Due o hei c ys al s uc u e-dependen
unable op ical p ope ies and high emission quan um yields, Mn-based pe o ski es a e
now being la gely conside ed in he de elopmen o new LED de ices and as e icien X- ay
scin illa o s [
37
,
38
]. Howe e , he e a e s ill se e al issues o esol e be o e hese ma e ials
a e applied. In his ega d, he des abiliza ion o Mn-based pe o ski es in mois u e is wo h
men ioning, as hey a e based on sal s. In he p esence o wa e , he ionic coo dina ion
bonds o Mn (II) cen e s can easily be des oyed o he ma e ial can unde go a phase
ans o ma ion p ocess, leading o a loss o he emission [
39
]. By hea ing o exposing hese
s uc u es o ap o ic sol en apo s, he pho oluminescence can be pa ially o almos
o ally eco e ed. These cha ac e is ics ha e been exploi ed o he ab ica ion o ew i able
PL pape s [
39
] and in he sensing o ace one [
40
]. Ano he issue o conside o a be e
unde s anding o Mn-based pe o ski e spec oscopy is o explo e he ole played by he
o ganic ligand on he s uc u e and pho obeha io . Few epo s ha e sugges ed he in-
ol emen o elec on-phonon in e ac ions in hei pho ochemis y [
29
–
31
]. To gain insigh
in o he elec onic s uc u e, he o igin o b igh pho oluminescence, and e omagne ic
coupling in hese kinds o ma e ials, se e al ab ini io models ha e been p oposed [
41
,
42
].
Recen ly, hese me hods ha e been applied o p edic he band s uc u es and alida e he
o igin o Mn
2+
pho oluminescence h ough spin o bidden
4
T
1→6
A
1
ansi ions o some
all-Mn halide pe o ski e single c ys als [16,17,38,40].
In . J. Mol. Sci. 2023,24, 3280 3 o 16
In his wo k, we syn hesized wo Mn (II)-based pe o ski es using a mono alen (e hyl
ammonium (EA) b omide) and a bi alen (e hyl diammonium (EDA) dib omide) in e laye
space ca ion. The esul ing pe o ski es, C
2
H
5
NH
3
MnB
3
(P1) and C
2
H
4
(NH
3
)
2
MnB
4
(P2), espec i ely, we e cha ac e ized by powde X- ay di ac ion echnique (PXRD,)
elec on-spin pa amagne ic esonance (EPR), s eady-s a e, and ime- esol ed emission
spec oscopy. We obse ed ha he P1 pe o ski e, ha ing mono alen ca ions, showed
o ange- ed emissions, while P2, based on bi alen in e laye space s, exhibi s g een pho-
oluminescence. This di e ence esul s om a dis inc Mn-coo dina ion (oc ahed al in P1
and e ahed al in P2). Fu he mo e, we ound ha P2 showed a highe pho oluminescence
quan um yield (26%) compa ed o 3.6% o P1. The pho oluminescence li e imes o P2 a e
0.10 and 0.37 ms, assigned o hyd a ed and non-hyd a ed phases in he pe o ski es, e-
spec i ely. The emission in ensi ies o bo h pe o ski es exhibi la ge sensi i i y o mois u e
(ai humidi y, 50–60%) and signi ican ly imp o ed s abili y upon encapsula ion wi hin a
poly(me hyl me hac yla e) (PMMA) ilm. The empe a u e e ec on he emission in ensi y
o P2 sugges s an ac i a ion ene gy ba ie ,
∆
E
a
= 4.46 kJ/mol (
∆
E
a
= 1.67 kJ/mol o P1)
o he non- adia i e p ocesses, mos p obably due o elec on-phonon in e ac ions. To he
bes o ou knowledge, his is he i s epo compa ing he e ec o mono- and bi alen
space ca ions bounded o he Mn cen e s in Mn-based pe o ski es, using he same ca bon
chain. We belie e ha ou esul s will help when designing new Mn(II) pe o ski es o
u he imp o emen o hei pho onic pe o mances.
2. Resul s and Discussion
2.1. S uc u al Cha ac e iza ion
The syn hesized pe o ski es (Scheme 1) we e cha ac e ized by powde X- ay di ac-
ion (PXRD) and EPR echniques (Figu e 1).
In . J. Mol. Sci. 2023, 24, x FOR PEER REVIEW 3 o 16
In his wo k, we syn hesized wo Mn (II)-based pe o ski es using a mono alen
(e hyl ammonium (EA) b omide) and a bi alen (e hyl diammonium (EDA) dib omide)
in e laye space ca ion. The esul ing pe o ski es, C
2
H
5
NH
3
MnB
3
(P1) and
C
2
H
4
(NH
3
)
2
MnB
4
(P2), espec i ely, we e cha ac e ized by powde X- ay di ac ion ech-
nique (PXRD,) elec on-spin pa amagne ic esonance (EPR), s eady-s a e, and ime- e-
sol ed emission spec oscopy. We obse ed ha he P1 pe o ski e, ha ing mono alen
ca ions, showed o ange– ed emissions, while P2, based on bi alen in e laye space s, ex-
hibi s g een pho oluminescence. This di e ence esul s om a dis inc Mn-coo dina ion
(oc ahed al in P1 and e ahed al in P2). Fu he mo e, we ound ha P2 showed a highe
pho oluminescence quan um yield (26%) compa ed o 3.6% o P1. The pho oluminescence
li e imes o P2 a e 0.10 and 0.37 ms, assigned o hyd a ed and non-hyd a ed phases in
he pe o ski es, espec i ely. The emission in ensi ies o bo h pe o ski es exhibi la ge
sensi i i y o mois u e (ai humidi y, 50–60 %) and signi ican ly imp o ed s abili y upon
encapsula ion wi hin a poly(me hyl me hac yla e) (PMMA) ilm. The empe a u e e ec
on he emission in ensi y o P2 sugges s an ac i a ion ene gy ba ie , ΔE
a
= 4.46 kJ/mol
(ΔE
a
= 1.67 kJ/mol o P1) o he non- adia i e p ocesses, mos p obably due o elec on–
phonon in e ac ions. To he bes o ou knowledge, his is he i s epo compa ing he
e ec o mono- and bi alen space ca ions bounded o he Mn cen e s in Mn-based pe -
o ski es, using he same ca bon chain. We belie e ha ou esul s will help when design-
ing new Mn(II) pe o ski es o u he imp o emen o hei pho onic pe o mances.
2. Resul s and Discussion
2.1. S uc u al Cha ac e iza ion
The syn hesized pe o ski es (Scheme 1) we e cha ac e ized by powde X- ay di ac-
ion (PXRD) and EPR echniques (Figu e 1).
Scheme 1. Chemical s uc u es o he uni s o C
2
H
5
NH
3
MnB
3
(P1) and C
2
H
4
(NH
3
)
2
MnB
4
(P2) pe -
o ski es using mono alen (e hyl ammonium b omide) and bi alen (e hyl diammonium dib o-
mide) o ganic space s, espec i ely. The dashed bond is an illus a ion o a possible H-bond be ween
he o ganic space and he Mn-b omide clus e o p oduce and main ain he pe o ski e s uc u e.
Figu e 1. (A) Room empe a u e powde X- ay di ac ion pa e ns o P1, P2, hyd a ed (unde a
wa e a mosphe e in a desicca o ) P2(H1), and P2(H2) pe o ski es. No e he inc ease in he peak
in ensi y o a ound 8.6° o P2, P2(H1), and P2(H2) upon exposu e o a wa e a mosphe e. (B) Room
empe a u e elec on-spin pa amagne ic esonance (EPR) spec a o P1 and P2 pe o ski es. The
Scheme 1.
Chemical s uc u es o he uni s o C
2
H
5
NH
3
MnB
3
(P1) and C
2
H
4
(NH
3
)
2
MnB
4
(P2) pe -
o ski es using mono alen (e hyl ammonium b omide) and bi alen (e hyl diammonium dib omide)
o ganic space s, espec i ely. The dashed bond is an illus a ion o a possible H-bond be ween he
o ganic space and he Mn-b omide clus e o p oduce and main ain he pe o ski e s uc u e.
In . J. Mol. Sci. 2023, 24, x FOR PEER REVIEW 3 o 16
In his wo k, we syn hesized wo Mn (II)-based pe o ski es using a mono alen
(e hyl ammonium (EA) b omide) and a bi alen (e hyl diammonium (EDA) dib omide)
in e laye space ca ion. The esul ing pe o ski es, C
2
H
5
NH
3
MnB
3
(P1) and
C
2
H
4
(NH
3
)
2
MnB
4
(P2), espec i ely, we e cha ac e ized by powde X- ay di ac ion ech-
nique (PXRD,) elec on-spin pa amagne ic esonance (EPR), s eady-s a e, and ime- e-
sol ed emission spec oscopy. We obse ed ha he P1 pe o ski e, ha ing mono alen
ca ions, showed o ange– ed emissions, while P2, based on bi alen in e laye space s, ex-
hibi s g een pho oluminescence. This di e ence esul s om a dis inc Mn-coo dina ion
(oc ahed al in P1 and e ahed al in P2). Fu he mo e, we ound ha P2 showed a highe
pho oluminescence quan um yield (26%) compa ed o 3.6% o P1. The pho oluminescence
li e imes o P2 a e 0.10 and 0.37 ms, assigned o hyd a ed and non-hyd a ed phases in
he pe o ski es, espec i ely. The emission in ensi ies o bo h pe o ski es exhibi la ge
sensi i i y o mois u e (ai humidi y, 50–60 %) and signi ican ly imp o ed s abili y upon
encapsula ion wi hin a poly(me hyl me hac yla e) (PMMA) ilm. The empe a u e e ec
on he emission in ensi y o P2 sugges s an ac i a ion ene gy ba ie , ΔE
a
= 4.46 kJ/mol
(ΔE
a
= 1.67 kJ/mol o P1) o he non- adia i e p ocesses, mos p obably due o elec on–
phonon in e ac ions. To he bes o ou knowledge, his is he i s epo compa ing he
e ec o mono- and bi alen space ca ions bounded o he Mn cen e s in Mn-based pe -
o ski es, using he same ca bon chain. We belie e ha ou esul s will help when design-
ing new Mn(II) pe o ski es o u he imp o emen o hei pho onic pe o mances.
2. Resul s and Discussion
2.1. S uc u al Cha ac e iza ion
The syn hesized pe o ski es (Scheme 1) we e cha ac e ized by powde X- ay di ac-
ion (PXRD) and EPR echniques (Figu e 1).
Scheme 1. Chemical s uc u es o he uni s o C
2
H
5
NH
3
MnB
3
(P1) and C
2
H
4
(NH
3
)
2
MnB
4
(P2) pe -
o ski es using mono alen (e hyl ammonium b omide) and bi alen (e hyl diammonium dib o-
mide) o ganic space s, espec i ely. The dashed bond is an illus a ion o a possible H-bond be ween
he o ganic space and he Mn-b omide clus e o p oduce and main ain he pe o ski e s uc u e.
Figu e 1. (A) Room empe a u e powde X- ay di ac ion pa e ns o P1, P2, hyd a ed (unde a
wa e a mosphe e in a desicca o ) P2(H1), and P2(H2) pe o ski es. No e he inc ease in he peak
in ensi y o a ound 8.6° o P2, P2(H1), and P2(H2) upon exposu e o a wa e a mosphe e. (B) Room
empe a u e elec on-spin pa amagne ic esonance (EPR) spec a o P1 and P2 pe o ski es. The
Figu e 1.
(
A
) Room empe a u e powde X- ay di ac ion pa e ns o P1, P2, hyd a ed (unde a
wa e a mosphe e in a desicca o ) P2(H1), and P2(H2) pe o ski es. No e he inc ease in he peak
in ensi y o a ound 8.6
◦
o P2, P2(H1), and P2(H2) upon exposu e o a wa e a mosphe e. (
B
) Room
empe a u e elec on-spin pa amagne ic esonance (EPR) spec a o P1 and P2 pe o ski es. The
na ow EPR spec um o P1 is a ypical signal o an oc ahed al Mn(II) cen e , while he la ge one o
P2 sugges s a e ahed al con igu a ion (see ex o mo e de ails).
In . J. Mol. Sci. 2023,24, 3280 4 o 16
The PXRD pa e ns o d ied P1 and P2, and hyd a ed P2 (sho exposu e, P2(H1) and
12-h exposu e, P2(H2)) (Figu e 1A) a e compa able o hose epo ed o simila Mn-based
pe o ski es, e lec ing hei c ys alline s uc u es. No ably, he PXRD o P1 p esen ed ewe
peaks in compa ison wi h hose o P2, P2(H1), and P2(H2), which sugges s a highe c ys-
allini y o he o me . Addi ionally, in he PXRD o P2, P2(H1), and P2(H2), we obse ed
he p esence o a peak a ~8.5
◦
, which inc eased in in ensi y when he pe o ski e c ys als
we e exposed o ambien condi ions and allowed o adso b wa e om he en i onmen
(P2(H1)). The PXRD pa e n o P2(H2) exposed o he ambien humidi y (50–60%) o a
longe ime (12 h) showed a no able inc ease in he in ensi y o he peak associa ed wi h
he hyd a ed quasi-oc ahed al phase a 8.5
◦
. Simila beha io wi h he appea ance o a
peak a a ound 10
◦
o ans-2,5-dime hylpipe azine Mn(II) b omide pe o ski e was e-
po ed upon adso p ion and coo dina ion o wa e molecules [
39
]. In ha pe o ski e, Mn
2+
adop ed a quasi-oc ahed al coo dina ion sphe e o p oduce a seconda y, non-emissi e
phase along wi h he g een emissi e e ahed ally-coo dina ed Mn
2+
ions. We belie e ha
upon hyd a ion, a popula ion o Mn(II) in P2 expe iences a simila change in he Mn
2+
ion
con igu a ion-gi ing s uc u es, such as P2(H1) and P2(H2).
I should be no ed ha ou a emp s o ob ain su icien ly la ge single c ys als o
pe o m X- ay expe imen s h ough slow sol en e apo a ion and an isol en p ocedu es
we e unsuccess ul. The inabili y o ob ain a mac oscopic single c ys al is mos p obably due
o he lexibili y o he linea alipha ic space s ha inhibi he g ow h o la ge c ys als [
43
,
44
].
In a ecen wo k, he impac o he o ganic A
0
si e ligand s uc u e on he o ma ion
o MAPbI
3
pe o ski e ilms was s udied in e ms o c ys alliza ion kine ics, p ecu so
solu ions, and c ys al phase composi ions [
43
]. The au ho s employed n-bu ylammonium
(n-BA
+
) and iso-bu ylammonium (iso-BA
+
) ligands and ound ha changing om he linea
n-BA
+
o he b anched iso-BA
+
molecule led o be e c ys al o ien a ion and imp o ed ilm
c ys allini y. The obse ed e ec was explained in e ms o he spon aneous o ma ion o
la ge clus e s (due o lowe en halpies o he accumula ion o iso-BA
+
e sus n-BA
+
ligand)
in he p ecu so solu ion o iso-BA
+
, which could ac as p e-nuclea ion si es o accele a e
he c ys alliza ion o 2D pe o ski es [
43
]. Addi ionally, o P2, which is syn hesized in an
aqueous HB medium, he p ecu so (p o ona ed EDA) is highly soluble in wa e (and
insoluble in almos any o he sol en ), which u he impedes he o ma ion o a single
P2-c ys al in his en i onmen . The e o e, we could no ob ain di ec in o ma ion abou
he s uc u es o P1 and P2, he in ol ed dis ances be ween he Mn clus e s, and he
ypes o in e ac ions.
EPR is a sui able echnique used o de e mine he oxida ion s a e, spin s a e, and local
coo dina ion o pa amagne ic ions. To his aim, X-band EPR spec a we e egis e ed on
powde ed samples o P1 and P2 a oom empe a u e. An ideally esol ed EPR spec um o
isola ed Mn
2+
ions consis s o i e signals co esponding o he ine s uc u e (S = 5/2) ha
u he spli s in o six lines due o he hype ine in e ac ions (
55
Mn, I = 5/2) [
45
]. Howe e ,
in he s udied samples, he s uc u es appea o be collapsed (Figu e 1B). The obse ed
esonances a e cen e ed a g alues e y close o he ee elec on one, as expec ed o
high-spin Mn
2+
ions since o bi al con ibu ions o hei magne ic momen s a e no expec ed
in ei he oc ahed al o e ahed al en i onmen s (
6
A
1g
and
6
A
1
e ms, espec i ely) [
46
].
The EPR spec um o P1 can be well- i ed by a single Lo en zian line wi h g = 2.007 and he
peak- o-peak linewid h, ∆Hpp = 12.1 mT. The absence o ine and/o hype ine s uc u es
and he Lo en zian shape o he cu e indica e an exchange na owing o he spec um
due o s ong magne ic in e ac ions ha a e age he local ields a ound he Mn
2+
ions in
his compound [
47
,
48
]. Simila spec a ha e been ound in o he hyb id pe o ski es wi h
manganese in oc ahed al en i onmen s [49,50].
On he con a y, he EPR spec um o he P2 sample shows a e y b oad and sligh ly
aniso opic line (g = 2.01;
∆
H
pp
= 140 mT), oge he wi h a e y weak and na owe signal
ha could co espond o a seconda y phase. The b oadened appea ance o he P2 spec um
can be a ibu ed o ei he dipole–dipole in e ac ions, incomple e esolu ion o he ine
s uc u e, o sho ening o he spin–la ice and/o spin–spin elaxa ion imes. I is well
In . J. Mol. Sci. 2023,24, 3280 5 o 16
known ha dipola in e ac ions modi y he local ields el by he elec on spins leading o
an inc ease in he linewid h. On he o he hand, dis o ions o he c ys alline ield emo e
he degene acy o he ee Mn
2+
g ound s a e
6
S
5/2
in o h ee K ame double s (
±
5/2,
±
3/2, and
±
1/2) enabling i e allowed EPR ansi ions o each o ien a ion. In powde
spec a, he a e aging and o e lapping o hese signals o en esul in b oad signals [
51
].
Mo eo e , when he dis o ion is high and leads o ze o- ield spli ing o he same o de as
he Zeeman spli ing, he EPR spec um is usually b oad because he spin sys em is s ongly
coupled o ib a ional modes and. hence, he elaxa ion imes become qui e sho [
52
,
53
].
The e o e, he la ge di e ence be ween line wid hs shown by he EPR spec a o P1 and P2
sugges s ha he en i onmen o he Mn
2+
ions is di e en in bo h cases. The ze o- ield
spli ing appea s o be highe o he P2 compound, as expec ed o manganese (II) in a
dis o ed e ahed al en i onmen [
54
]. Thus, al hough we do no ha e a s uc u e based on
single c ys al X- ay expe imen s, om hese EPR esul s, he colo o he obse ed emission
o P1 (o ange/ ed) and P2 (g een), and he published epo s on Mn-based pe o ski es,
we belie e ha Mn
2+
ions in he o me ha e oc ahed al coo dina ion, while in he la e
i is a e ahed al one (Scheme 1). In hese p oposed s uc u es, whe e an Mn-b omide
clus e in e ac s wi h he ammonium g oup o p o ona ed EA and EDA space s, we in oke
he o ma ion o H-bonds o o m and main ain he pe o ski e s uc u e, as i has been
epo ed in o he epo s. [
15
,
38
,
55
] Thus, in he ollowing sec ions, we adop he molecula
s uc u es o he complexes shown in Scheme 1.
2.2. Pho ophysical Cha ac e iza ion
2.2.1. S eady-S a e UV-Visible Spec oscopy
To gain insigh in o he pho obeha io o hese pe o ski es, we eco ded solid-s a e
UV– is di use e lec ance, exci a ion, and emission spec a a ambien condi ions (Figu e 2).
The di use e lec ance and he exci a ion spec a p esen se e al s ong peaks a he UV
and isible egions. They e lec an elec onic ansi ion om he
6
A
1
(S) low-lying s a e o
Mn
2+
ions o he exci ed s a es o he MnB
x
clus e s [
28
]. We obse ed no dependence o
he exci a ion spec a wi h he emission wa eleng h.
In . J. Mol. Sci. 2023, 24, x FOR PEER REVIEW 5 o 16
ha could co espond o a seconda y phase. The b oadened appea ance o he P2 spec-
um can be a ibu ed o ei he dipole–dipole in e ac ions, incomple e esolu ion o he
ine s uc u e, o sho ening o he spin–la ice and/o spin–spin elaxa ion imes. I is well
known ha dipola in e ac ions modi y he local ields el by he elec on spins leading
o an inc ease in he linewid h. On he o he hand, dis o ions o he c ys alline ield e-
mo e he degene acy o he ee Mn2+ g ound s a e 6S5/2 in o h ee K ame double s (±5/2,
±3/2, and ±1/2) enabling i e allowed EPR ansi ions o each o ien a ion. In powde spec-
a, he a e aging and o e lapping o hese signals o en esul in b oad signals [51]. Mo e-
o e , when he dis o ion is high and leads o ze o- ield spli ing o he same o de as he
Zeeman spli ing, he EPR spec um is usually b oad because he spin sys em is s ongly
coupled o ib a ional modes and. hence, he elaxa ion imes become qui e sho [52,53].
The e o e, he la ge di e ence be ween line wid hs shown by he EPR spec a o P1 and
P2 sugges s ha he en i onmen o he Mn2+ ions is di e en in bo h cases. The ze o- ield
spli ing appea s o be highe o he P2 compound, as expec ed o manganese (II) in a
dis o ed e ahed al en i onmen [54]. Thus, al hough we do no ha e a s uc u e based
on single c ys al X- ay expe imen s, om hese EPR esul s, he colo o he obse ed
emission o P1 (o ange/ ed) and P2 (g een), and he published epo s on Mn-based pe -
o ski es, we belie e ha Mn2+ ions in he o me ha e oc ahed al coo dina ion, while in
he la e i is a e ahed al one (Scheme 1). In hese p oposed s uc u es, whe e an Mn-
b omide clus e in e ac s wi h he ammonium g oup o p o ona ed EA and EDA space s,
we in oke he o ma ion o H-bonds o o m and main ain he pe o ski e s uc u e, as i
has been epo ed in o he epo s. [15,38,55] Thus, in he ollowing sec ions, we adop he
molecula s uc u es o he complexes shown in Scheme 1.
2.2. Pho ophysical Cha ac e iza ion
2.2.1. S eady-S a e UV-Visible Spec oscopy
To gain insigh in o he pho obeha io o hese pe o ski es, we eco ded solid-s a e
UV– is di use e lec ance, exci a ion, and emission spec a a ambien condi ions (Figu e
2). The di use e lec ance and he exci a ion spec a p esen se e al s ong peaks a he
UV and isible egions. They e lec an elec onic ansi ion om he 6A1(S) low-lying s a e
o Mn2+ ions o he exci ed s a es o he MnB x clus e s [28]. We obse ed no dependence
o he exci a ion spec a wi h he emission wa eleng h.
Figu e 2. No malized o he maximum in ensi y o (A) abso p ion (dashed line), exci a ion (obse -
a ion a 600 nm, ed line), and emission (exci a ion a 430 nm, blue line) spec a o (A) P1 and (B)
P2 pe o ski es. The dashed line in (B) ep esen s he abso p ion spec um o P2(H1) exposed o a
wa e a mosphe e and shows a ela i e inc ease in he in ensi y o he abso p ion peak a a ound
470 nm. The inse s in bo h panels show he images o he pe o ski e unde ambien oom ligh ( op)
and 365 nm lamp i adia ion (bo om).
Fi s , we show and discuss he esul s o P1. The peaks in he di use e lec ance and
he exci a ion spec a a e loca ed a a ound 366, 377 (a shoulde ), 427, 438 (a shoulde ),
and 524 nm. These a ise om he 6A1(S) → 4E(D), 6A1(S)→ 4T2(D), 6A1(S) → (4A1, 4E(G)),
6A1(S) →4T2(G) and 6A1(S) → 4T1(G) ansi ions o he Mn2+ ions, espec i ely (Figu e 2A).
Figu e 2.
No malized o he maximum in ensi y o (
A
) abso p ion (dashed line), exci a ion (obse -
a ion a 600 nm, ed line), and emission (exci a ion a 430 nm, blue line) spec a o (
A
) P1 and
(
B
) P2 pe o ski es. The dashed line in (
B
) ep esen s he abso p ion spec um o P2(H1) exposed o a
wa e a mosphe e and shows a ela i e inc ease in he in ensi y o he abso p ion peak a a ound
470 nm. The inse s in bo h panels show he images o he pe o ski e unde ambien oom ligh (
op
)
and 365 nm lamp i adia ion (bo om).
Fi s , we show and discuss he esul s o P1. The peaks in he di use e lec ance and
he exci a ion spec a a e loca ed a a ound 366, 377 (a shoulde ), 427, 438 (a shoulde ),
and 524 nm. These a ise om he
6
A
1
(S)
→4
E(D),
6
A
1
(S)
→4
T
2
(D),
6
A
1
(S)
→
(
4
A
1
,
4
E(G)),
6
A
1
(S)
→4
T
2
(G) and
6
A
1
(S)
→4
T
1
(G) ansi ions o he Mn
2+
ions, espec i ely (Figu e 2A).
Mos impo an ly, he peaks a 427 and 524 nm a e ypical ea u es o oc ahed ally coo -
In . J. Mol. Sci. 2023,24, 3280 6 o 16
dina ed Mn
2+
ions [
28
]. P1 displays a ed-ligh emission upon UV–ligh i adia ion and
i s emission spec um consis s o a single band loca ed a 602 nm wi h a ull wid h a
hal maximum (FWHM) in ensi y o 70 nm (1932 cm
−1
) ha is independen o he exci-
a ion wa eleng h (Figu e 2A). Based on p e ious epo s o Mn-based pe o ski es and
he obse ed o ange/ ed emission o P1, we sugges oc ahed al coo dina ion o Mn
2+
in
his phase, in ag eemen wi h he EPR esul s [
17
,
28
,
39
]. The measu ed pho oluminescen
quan um yield (PLQY) o P1 gi es a alue o 3.6%, which is lowe han he one o P2
ha ing wo ammonia cen e s o in e ac wi h wo [MnB 4]2- clus e s.
Fo P2, he in ense peaks in he exci a ion spec um collec ed a 545 nm a e lo-
ca ed a a ound 362, 371, 389, 435, 449, and 465 nm and acco ding o he li e a u e hey
a ise om he
6
A
1
(S)
→4
T
2
(P),
6
A
1
(S)
→4
E(D),
6
A
1
(S)
→4
T
2
(D),
6
A
1
(S)
→
(
4
A
1
,
4
E(G)),
6
A
1
(S)
→4
T
2
(G) and
6
A
1
(S)
→4
T
1
(G) ansi ions o he Mn
2+
ions (such as in P1), espec-
i ely (Figu e 2B). The posi ions o hese peaks a e consis en wi h he ene gy s a es spli ing
o Mn
2+
in a e ahed al en i onmen [
28
]. No ably, he di use e lec ance spec um o
P2 shows he p esence o addi ional peaks a 425 and 510 nm ha mos p obably a ise
om a seconda y popula ion o Mn
2+
ions wi h quasi-oc ahed al coo dina ion [
39
]. The
p esence o his seconda y phase is u he suppo ed by he PXRD and EPR esul s, as
discussed abo e, and by he di use e lec ance spec um o he hyd a ed P2 (P2(H1)),
whe e he in ensi y o hese peaks inc eases (dashed line, Figu e 2B). Howe e , con a y o
he epo ed emissi e beha io o Mn
2+
wi h oc ahed al coo dina ion in o he Mn-based
hyb id ma e ials, [
28
,
37
,
56
] o P2 (and P2(H1)), he di e ence in he ela i e in ensi y o
he peaks in he di use e lec ance and exci a ion spec a indica es ha hese hyd a ed
Mn(II) cen e s a e non- o weakly-emissi e. Recen ly, i was sugges ed ha he emissi e
e ahed al Mn
2+
ions in ans-2,5-dime hylpipe azine manganese (II) b omide can be ans-
o med o a non-emissi e hyd a ed phase by adso bing wa e molecules and he Mn
2+
ions
could adop a quasi-oc ahed al coo dina ion sphe e [
39
]. Thus, he peaks obse ed in he
di use e lec ance spec a o P2 and P2(H1) a 425 and 510 nm a ise om he non-emissi e
seconda y hyd a ed phase. The o igin o his phase could be due o he ecap u ing o
wa e molecules om he ambien a mosphe e (humidi y o 50–60%). On he o he hand,
i could be he esul o he syn hesis p ocedu e, whe e wa e is he used sol en (HB ,
48% aqueous solu ion) and i could coo dina e wi h Mn
2+
o p oduce he non-emissi e
popula ion wi h oc ahed al coo dina ion. Unde UV–ligh i adia ion (365 nm) P2 emi s a
s ong g een ligh s emming om he highly localized in a-a omic Mn
2+
d-d ansi ions
(inse o Figu e 2B) [
28
]. The emission spec um consis s o a single band wi h he max-
imum in ensi y loca ed a 544 nm and he FWHM a 53 nm (1742 cm
−1
), which is also
independen o he exci a ion wa eleng h (Figu e 2B). Nex , we measu ed he PLQY a
ambien condi ions. The ob ained PLQY alue o 26% is la ge, bu lowe in compa ison
wi h o he g een-emissi e Mn-based hyb id ma e ials wi h e ahed al coo dina ion ha
ha e epo ed alues >80% [
15
,
25
,
26
,
36
,
39
,
40
,
57
]. The mos p obable explana ion o he
obse ed disc epancy is he p esence o he non-emissi e hyd a ed phase wi h oc ahed al
coo dina ion o he Mn2+ ions in ou pe o ski e.
To suppo his explana ion, we eco ded he emission in ensi y o he nea c ys als
o P1 and P2 exposed o ai and o c ys als co e ed by a PMMA ilm o e long pe iod o
ime (Figu e 3). While he emission in ensi y o he nea c ys als d as ically d ops wi h ime
(100% in 6 h o P1 and in 8 h o P2) due o he adso p ion o wa e , upon p o ec ion wi h a
PMMA ilm, he in ensi y ini ially d ops by only 25% a e 40 h o P2 and 20% a e 25 h
o P1. Following his ini ial d op, he emission in ensi y o he p o ec ed P2 ema kably
emains cons an o a long ime (1000 h). The ini ial d op in he emission in ensi y o
he PMMA-p o ec ed samples a he i s hou s is mos p obably due o in e ac ion o he
pe o ski e c ys als wi h he used sol en ( oluene) o p epa e he PMMA ilm.
In . J. Mol. Sci. 2023,24, 3280 7 o 16
In . J. Mol. Sci. 2023, 24, x FOR PEER REVIEW 7 o 16
Figu e 3. Change (due o ambien humidi y, 50–60%) in he emission in ensi y maximum (no mal-
ized o 1) wi h hou s o syn hesized nea (A) P1 and (B) P2, p o ec ed wi h a PMMA ilm. Bo h
samples we e s o ed a ambien condi ions. The ini ial changes in emission in ensi y o P1/PMMA
and P2/PMMA a e mos p obably due o he in e ac ion o he c ys als wi h oluene used o p epa e
he PMMA ilm. No ice he la ge s abili y upon encapsula ion by a PMMA ilm. The exci a ion
wa eleng h was 370 nm.
Now, we u n ou a en ion o he di e ences in he s eady-s a e abso p ion and emis-
sion spec a o P1 and P2 and compa e hem wi h hose o o he Mn-based pe o ski es.
Se e al ac o s a e expec ed o con ibu e o he pho ophysical beha io o he s udied
s uc u es, some o which a e mo e speci ic o Mn2+-pe o ski es, such as he Mn-Mn dis-
ances and elec on–phonon couplings, while o he s a e mo e gene al and can be ex ap-
ola ed om o he ypes o pe o ski es (such as H-bonding and o he non-co alen in e -
ac ions o s uc u al a angemen [58–60]). Rela ed o he s uc u e, we belie e ha he
obse ed di e ence in he beha io o P1 and P2 could s em om di e ences in he s uc-
u al a angemen o he Mn-b omide clus e s due o he used o ganic ligand. We hypo h-
esize ha he EA o ganic monoca ion in P1 mos p obably gi es ise o ei he a 3D hyb id
o ganic–ino ganic pe o ski e (HOIP), BMX3 (B = small o ganic ca ion; X = halide and M =
me al) o a s uc u e simila o Ruddlesden–Poppe -like 2D laye ed HOIP [60,61]. In bo h
cases, hese allow o sho e dis ances be ween he luminescen Mn cen e s esul ing in a
s onge coupling. On he o he hand, he EDA dica ion in P2 is expec ed o gi e ise o
Dion–Jacobson-like 2D HOIP laye ed s uc u es. In hese, we expec ha he s uc u es
exhibi pe ec s acking wi h no o se o displacemen be ween successi e laye s, which
can be a ibu ed o he single laye o ions be ween each laye , as has been epo ed o
o he pe o ski es [61].
The s uc u al o ganiza ion o P1 and P2 is closely ela ed o he coo dina ion sphe e
o Mn2+. I is well es ablished ha he linea chain o he oc ahed on coo dina ion, such as
in he P1 sample, gi es ise o a sys em o exchange-coupled Mn2+ ions since he nea es
Mn-Mn dis ance is much sho e (3–5 Å) han ha o Mn-Mn wi hin he nea es neighbo -
ing chain [18,28,37,56]. This enables in achain Mn-Mn coupling se e al o de s o magni-
ude s onge han he in e chain Mn-Mn coupling. Thus, he Mn2+ ions a angemen in
hese sys ems p o ides exci onic con inemen gi ing ise o a subs an ial educ ion o ex-
ci on cap u e by non adia i e aps. In addi ion o ha , he in e ac ion be ween he nea es
Mn2+ ions wi hin he linea chain is bene icial o enhancing Mn2+ abso p ion [28,37,56].
Fu he mo e, i was sugges ed ha o sys ems wi h e ahed al a angemen s, such as P2,
he Mn-con aining [MnB 4]2− e ahed on is indi idually isola ed among he c ys al la ice
and sepa a ed om he o he e ahed ons by he la ge o ganic ca ion (EDA in he case o
P2) [25,37,62]. The longe dis ance be ween wo neighbo ing [MnB 4]2- e ahed a, which
is es ima ed be ween ~7 and 10 Å, can educe he Mn-Mn in e ac ion and hence signi i-
can ly inhibi he concen a ion quenching e ec o Mn2+ by supp essing he mig a-
ion/dissipa ion o exci a ion ene gy o adjacen luminescen cen e s o Mn2+ [25,27]. As a
esul , i is possible ha longe Mn-Mn dis ances would enable all Mn2+ luminescen
Figu e 3.
Change (due o ambien humidi y, 50–60%) in he emission in ensi y maximum (no malized
o 1) wi h hou s o syn hesized nea (
A
) P1 and (
B
) P2, p o ec ed wi h a PMMA ilm. Bo h samples
we e s o ed a ambien condi ions. The ini ial changes in emission in ensi y o P1/PMMA and
P2/PMMA a e mos p obably due o he in e ac ion o he c ys als wi h oluene used o p epa e
he PMMA ilm. No ice he la ge s abili y upon encapsula ion by a PMMA ilm. The exci a ion
wa eleng h was 370 nm.
Now, we u n ou a en ion o he di e ences in he s eady-s a e abso p ion and emis-
sion spec a o P1 and P2 and compa e hem wi h hose o o he Mn-based pe o ski es.
Se e al ac o s a e expec ed o con ibu e o he pho ophysical beha io o he s udied
s uc u es, some o which a e mo e speci ic o Mn
2+
-pe o ski es, such as he Mn-Mn
dis ances and elec on-phonon couplings, while o he s a e mo e gene al and can be ex-
apola ed om o he ypes o pe o ski es (such as H-bonding and o he non-co alen
in e ac ions o s uc u al a angemen [
58
–
60
]). Rela ed o he s uc u e, we belie e ha
he obse ed di e ence in he beha io o P1 and P2 could s em om di e ences in he
s uc u al a angemen o he Mn-b omide clus e s due o he used o ganic ligand. We
hypo hesize ha he EA o ganic monoca ion in P1 mos p obably gi es ise o ei he a 3D
hyb id o ganic–ino ganic pe o ski e (HOIP), BMX
3
(B = small o ganic ca ion; X = halide
and M = me al) o a s uc u e simila o Ruddlesden–Poppe -like 2D laye ed HOIP [
60
,
61
].
In bo h cases, hese allow o sho e dis ances be ween he luminescen Mn cen e s e-
sul ing in a s onge coupling. On he o he hand, he EDA dica ion in P2 is expec ed o
gi e ise o Dion–Jacobson-like 2D HOIP laye ed s uc u es. In hese, we expec ha he
s uc u es exhibi pe ec s acking wi h no o se o displacemen be ween successi e laye s,
which can be a ibu ed o he single laye o ions be ween each laye , as has been epo ed
o o he pe o ski es [61].
The s uc u al o ganiza ion o P1 and P2 is closely ela ed o he coo dina ion sphe e
o Mn
2+
. I is well es ablished ha he linea chain o he oc ahed on coo dina ion, such
as in he P1 sample, gi es ise o a sys em o exchange-coupled Mn
2+
ions since he
nea es Mn-Mn dis ance is much sho e (3–5 Å) han ha o Mn-Mn wi hin he nea es
neighbo ing chain [
18
,
28
,
37
,
56
]. This enables in achain Mn-Mn coupling se e al o de s
o magni ude s onge han he in e chain Mn-Mn coupling. Thus, he Mn
2+
ions a -
angemen in hese sys ems p o ides exci onic con inemen gi ing ise o a subs an ial
educ ion o exci on cap u e by non adia i e aps. In addi ion o ha , he in e ac ion
be ween he nea es Mn
2+
ions wi hin he linea chain is bene icial o enhancing Mn
2+
abso p ion [
28
,
37
,
56
]. Fu he mo e, i was sugges ed ha o sys ems wi h e ahed al a -
angemen s, such as P2, he Mn-con aining [MnB
4
]
2−
e ahed on is indi idually isola ed
among he c ys al la ice and sepa a ed om he o he e ahed ons by he la ge o ganic
ca ion (EDA in he case o P2) [
25
,
37
,
62
]. The longe dis ance be ween wo neighbo ing
[MnB
4
]
2−
e ahed a, which is es ima ed be ween ~7 and 10 Å, can educe he Mn-Mn
In . J. Mol. Sci. 2023,24, 3280 8 o 16
in e ac ion and hence signi ican ly inhibi he concen a ion quenching e ec o Mn
2+
by
supp essing he mig a ion/dissipa ion o exci a ion ene gy o adjacen luminescen cen e s
o Mn
2+
[
25
,
27
]. As a esul , i is possible ha longe Mn-Mn dis ances would enable all
Mn
2+
luminescen cen e s o emi simul aneously unde exci a ion i espec i e o c ys al
de ec s he eby achie ing a highe PLQY. Fu he mo e, in p e ious s udies ha ha e e-
po ed no ably highe PLQY, he used o ganic ca ions ende ed signi ican ly mo e igid
s uc u es [
15
,
25
,
28
,
33
,
37
,
39
,
62
]. This inc eased igidi y can educe he he mal ib a ion o
he ino ganic anions, which in u n can supp ess he non- adia i e ansi ions and esul
in a signi ican ly highe PLQY. In P1 and P2, he o ganic ca ions ha e linea chains ha
ende highe lexibili y in he esul ing la ice, which would enhance he elec on-pho on
in e ac ions and migh in pa explain he ela i ely lowe PLQY alues.
Independen ly on whe he he ob ained s uc u es a e 3D o 2D HOIP, he s eng h o
he non-co alen in e ac ions (H-bonding, halogen bonding, an de Waals, o name a ew)
plays a signi ican ole in he s uc u al s abili y and phase ans o ma ion [
58
–
60
,
63
]. In
hese s uc u es, he o ganic ca ions in e ac wi h he su ounding me al clus e s h ough
weak seconda y H-bonding, wi h ene gies lowe han 0.1 eV pe bond [
58
,
64
]. DFT calcu-
la ions on MAPbX
3
(MA = me hyl ammonium; X = B o I) ha e e ealed he ole o he
di e en H-bonding in e ac ions in he s abili y o he pe o ski e ne wo k [
65
,
66
]. Due o
hese weak in e ac ion ene gies, he eo ien a ion o he o ganic ca ion can be ac i a ed
ei he he mally a a ini e empe a u e o by applying mechanical s imuli. A combined
heo e ical and expe imen al s udy has demons a ed a dynamical change in he elec onic
band s uc u es and
∼
60- old pho oluminescence enhancemen upon cooling in MAPbB
3
hyb id pe o ski es. These we e explained in e ms o a dec ease in he deg ee o o a-
ional eedom o MA due o a change in he H-bonding in e ac ions. H-bonding can
also in luence he mechanical p ope ies o pe o ski e sys ems [
67
]. A ecen s udy has
epo ed on wo Mn-based me al-o ganic amewo k pe o ski es [C(NH
2
)
3
][Mn(HCOO)
3
]
and [(CH
2
)
3
NH
2
][Mn(HCOO)
3
] wi h he o me gi ing highe Young’s moduli and ha d-
ness due o he s onge hyd ogen bonding be ween he amewo k hos s and he amine
ca ions [
68
]. Addi ionally, in he 2D HOIP, he ino ganic and o ganic laye s a e connec ed
ia H-bonds, which p o ide s uc u al s abili y o he o e all geome y. I has been shown
o some Mn (II)-based hyb id pe o ski es ha s onge H-bonding in e ac ions lead o
la ge PLQY [
15
,
38
,
55
]. Finally, o he s udied samples he e, one also needs o ake in o
conside a ion he p esence o he hyd a ed non-emissi e oc ahed al phase ha can u he
educe he PLQY and a ec hei exci ed s a e dynamics.
To ob ain mo e insigh in o he emission beha io , we eco ded he emission decays,
o be shown and discussed in Sec ion 2.2.2. We i s examine he empe a u e e ec on
he emission spec um o P2. Recen epo s ha e shown ha a change in he empe a u e
induces a con e sion om one Mn(II) con igu a ion o ano he one [
31
,
69
–
71
]. This e ec
is e lec ed in he emission colo ha swi ches om g een o o ange/ ed when he em-
pe a u e inc eases, and he e e se when he empe a u e dec eases [
31
,
69
]. The he mal
s abili y o Mn-based pe o ski es is well documen ed, and he mog a ime ic analysis
o (CH
6
N
3
)
2
MnCl
4
and 1-(2-aminoe hyl)pipe azine MnB , o example, has shown la ge
s abili y up o 573 K [
38
,
72
]. Thus, we explo ed he e ec o he empe a u e ( om 30 o
125
◦
C) on he emission spec um o P1 and P2. To begin wi h P2, he esul s show a clea
g adual dec ease in in ensi y wi h he inc ease in empe a u e ha does no anish a 125
◦
C
(Figu e 4). The ela i ely small obse ed he mal quenching in he s udied empe a u e
ange sugges s a ela i ely long Mn-Mn dis ance. We also obse ed a small b oadening o
he emission band (inse o Figu e 4). These esul s can be in e p e ed in e ms o he open-
ing o a non- adia i e p ocess o by he con e sion o he Mn(II) e ahed al con igu a ion
in P2 o an oc ahed al one. Howe e , we did no obse e any o ange/ ed emission, he
signa u e o he Mn(II) oc ahed al en i onmen , as eco ded o P1 (Figu e 2A). Thus, we
sugges ha he dec ease in he emission in ensi y o P2 upon inc easing he empe a u e
is a he due o an inc ease in he non- adia i e p ocesses, which a e enhanced when
elec on-phonon in e ac ions inc ease [
31
,
71
]. No ice ha we did no obse e any change in
In . J. Mol. Sci. 2023,24, 3280 9 o 16
he exci a ion spec a upon inc easing he empe a u e by almos 100
◦
C, which indica es
ha he emi e s o P2 a e o igina ing om he same g ound s a e popula ion (Figu e S1).
We also calcula ed he ac i a ion ene gy ba ie o he non- adia i e p ocesses o P2,
∆
E
a
,
ollowing Equa ion (1) [38]:
I(T) = I0
1+Aexp−∆Ea
kBT(1)
whe e I(T) and I
0
a e he luo escence in ensi ies a empe a u es Tand T
0
(303 K, 30
◦
C),
espec i ely, A is he p e-exponen ial ac o ,
∆
E
a
is he ac i a ion ene gy ba ie o non-
adia i e p ocesses and k
B
is he Bol zmann cons an . The i o he empe a u e depen-
dence o he emission in ensi y maximum gi es
∆
E
a
= 4.46 kJ/mol (Figu e S2A). Fo P1,
∆
E
a
= 1.67 kJ/mol, which is abou 3–4 imes lowe han ha o P2, in ag eemen wi h
he end in he PLQY alues o hese pe o ski es (Figu e S2B). No e also ha he he mal
ene gy a oom empe a u e (2.45 kJ/mol a 298 K) is sligh ly la ge han
∆
E
a
o P1 in
ag eemen wi h i s low PLQY. These ene gy ba ie s a e lowe han he one epo ed o
(CH6N3)2MnCl4pe o ski e (11.74 kJ/mol), ha ing a PLQY o 55.9% [38].
In . J. Mol. Sci. 2023, 24, x FOR PEER REVIEW 9 o 16
We also calcula ed he ac i a ion ene gy ba ie o he non- adia i e p ocesses o P2,
ΔEa, ollowing Equa ion (1) [38]:
𝐼𝑇= 𝐼
1+Aexp−∆𝐸
𝑘𝑇 (1)
whe e I(T) and I0 a e he luo escence in ensi ies a empe a u es T and T0 (303 K, 30 °C),
espec i ely, A is he p e-exponen ial ac o , ΔEa is he ac i a ion ene gy ba ie o non-
adia i e p ocesses and kB is he Bol zmann cons an . The i o he empe a u e depend-
ence o he emission in ensi y maximum gi es ΔEa = 4.46 kJ/mol (Figu e S2A). Fo P1, ΔEa
= 1.67 kJ/mol, which is abou 3–4 imes lowe han ha o P2, in ag eemen wi h he end
in he PLQY alues o hese pe o ski es (Figu e S2B). No e also ha he he mal ene gy a
oom empe a u e (2.45 kJ/mol a 298 K) is sligh ly la ge han ΔEa o P1 in ag eemen
wi h i s low PLQY. These ene gy ba ie s a e lowe han he one epo ed o
(CH6N3)2MnCl4 pe o ski e (11.74 kJ/mol), ha ing a PLQY o 55.9% [38].
Figu e 4. Tempe a u e dependence o he emission spec um o P2 collec ed a he indica ed em-
pe a u es. The inse shows he same emission spec a no malized a he maximum emission in en-
si y. The exci a ion wa eleng h was 430 nm.
2.2.2. Time-Resol ed Emission Da a
To explo e he pho odynamical p ope ies o he wo Mn-based pe o ski es, we col-
lec ed hei emission decays in a PMMA ma ix a se e al emission wa eleng hs upon
exci a ion a 371 and 433 nm. No no able exci a ion and emission wa eleng h dependence
was obse ed o bo h samples (Figu e S3 and Table S1). The emission decays o bo h
pe o ski es in he PMMA ma ix decay biexponen ially wi h ime cons an s o τ1 = 83 µs
(53%) and τ2 = 250 µs (47%) o P1, and τ1 = 100 µs (9%) and τ2 = 370 µs (91%) o P2 (Figu e
5 and Table 1). These alues gi e a e age li e imes o τAVE = 212 µs and τAVE = 362 µs o
P1 and P2, espec i ely. The la ge alue o τAVE o P2 ag ees wi h i s highe PLQY (26%)
when compa ed o P1 (3.6%).
Figu e 4.
Tempe a u e dependence o he emission spec um o P2 collec ed a he indica ed empe a-
u es. The inse shows he same emission spec a no malized a he maximum emission in ensi y.
The exci a ion wa eleng h was 430 nm.
2.2.2. Time-Resol ed Emission Da a
To explo e he pho odynamical p ope ies o he wo Mn-based pe o ski es, we col-
lec ed hei emission decays in a PMMA ma ix a se e al emission wa eleng hs upon
exci a ion a 371 and 433 nm. No no able exci a ion and emission wa eleng h dependence
was obse ed o bo h samples (Figu e S3 and Table S1). The emission decays o bo h pe -
o ski es in he PMMA ma ix decay biexponen ially wi h ime cons an s o
τ1= 83 µs (53%)
and
τ2
= 250
µ
s (47%) o P1, and
τ1
= 100
µ
s (9%) and
τ2
= 370
µ
s (91%) o P2 (Figu e 5
and Table 1). These alues gi e a e age li e imes o
τAVE
= 212
µ
s and
τAVE
= 362
µ
s o
P1 and P2, espec i ely. The la ge alue o
τAVE
o P2 ag ees wi h i s highe PLQY (26%)
when compa ed o P1 (3.6%).
In . J. Mol. Sci. 2023,24, 3280 16 o 16
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Disclaime /Publishe ’s No e:
The s a emen s, opinions and da a con ained in all publica ions a e solely hose o he indi idual
au ho (s) and con ibu o (s) and no o MDPI and/o he edi o (s). MDPI and/o he edi o (s) disclaim esponsibili y o any inju y o
people o p ope y esul ing om any ideas, me hods, ins uc ions o p oduc s e e ed o in he con en .
