A oma ici y Ho Pape
HowA oma ic A e Molecula Nano ings?The Case o
aSix-Po phy in Nano ing**
I ene Casademon -Reig,RaffllGue e o-A il8s, EloyRamos-Co doba,*
Miquel To en -Suca a ,* and Edua dMa i o*
Dedica ed o he memo y o ou iend and colleague,P o .Is #nMaye ,whose wo ks ha e been acon inuous inspi a ion
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In e na ional Edi ion: doi.o g/10.1002/anie.202108997
Ge man Edi ion: doi.o g/10.1002/ange.202108997
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Abs ac : La ge conjuga ed ings wi h pe sis en cu en s a e
no el p omising s uc u es in molecula -scale elec onics.A
six-po phy in nano ing s uc u e ha allegedly sus ained an
a oma ic ing cu en in ol ing 78pelec ons was ecen ly
syn hesized.Wep o ide he e compelling e idence ha his
molecule is no a oma ic,con a y o wha was in e ed om
he analysis o 1H-NMR da a and compu a ional calcula ions
ha su e om la ge delocaliza ion e o s.The main eason
behind he absence o an a oma ic ing cu en in hese
nano ings is he low delocaliza ion in he ansi ion om he
po phy ins o he b idging bu adiyne linke s,which dis up s
he o e all conjuga ed ci cui . These esul s highligh he
impo ance o choosing asui able compu a ional me hod o
s udy la ge conjuga ed molecules and he app op ia e a oma-
ici y desc ip o s o iden i y he pa o he molecule esponsible
o he loss o a oma ici y.
In oduc ion
Benzene is he pa adigm o an o ganic a oma ic molecule,
exhibi ing bond-leng h equaliza ion, cyclic elec on delocal-
iza ion, and exal ed magne ic suscep ibili y.Assuch, benzene
is jus he smalles neu al annulene ha p esen s p-con-
juga ed a oma ici y;o
he annulenes possessing 4n+2p
elec ons a e also conside ed a oma ic. I is well es ablished
ha la ge annulenes su e ou -o -plane dis o ions and
exhibi apoo o e lap be ween po bi als, hus a o ing
non-symme ic con o ma ions ha a e much less a oma ic.[1–3]
Thela ge he annulene, he less a oma ic he molecule is
expec ed o be.Fo his eason, i is di icul o ind la ge
a oma ic mac ocycles.[2,4,5] Geome ical cons ain s a e im-
posed in some la ge mac ocyclic s uc u es wi h he hope o
p ese e conjuga ion, a oma ici y,and quan um cohe ence.
Among he molecules wi h he la ges a oma ic ings,i is
wo h highligh ing he dodecaphy in s uc u es syn hesized
by Osuka and co-wo ke s,[6,7] which adop wis ed Mçbius and
Hgckel con o ma ions, he annulene-wi h-an-annulene a o-
ma ic supe - ing s uc u e o Wu e al.,[8] and he p-conju-
ga ed six-po phy in nano ing o Ande son and co-wo ke s
(see Figu e 1).[9] Thela e wo k syn hesized and analyzed he
a oma ici y o asix-po phy in nano ing (c-P6·T6) in ou
di e en oxida ion s a es (c-P6·T6, c-P6·T64+,c-P6·T66+,and
c-P6·T612+), concluding om 1H-NMR, NICS,and ACID
analyses ha he neu al and he c-P6·T612+species a e non-
a oma ic,whe eas c-P6·T64+and c-P6·T66+a e, espec i ely,
an ia oma ic and a oma ic.[9,10] These molecules we e he i s
o ase ies o simila la ge mac ocyclic s uc u es exhibi ing
(an i)a oma ici y.[9,11–14]
Po phy in nano ings a e e y a ac i e compounds
because hey o e an end- ee p-conjuga ed sys em wi h
ema kable p ope ies such as pho ophysical and gues -
encapsula ing,which migh lead o amy iad o applica ions
in he ield o single-molecule elec onics,[15,16] se e as ligh -
ha es ing an ennas,[17] o in es iga e ene gy ans e in
biomime ic sys ems,[18] among o he s.[9,13,19–25] In his sense,
he in e es and he u ili y o he compounds syn hesized by
he g oup o Ande son a e beyond ques ion. Howe e ,in his
wo k, we demons a e ha he a oma ici y o hese la ge
mac ocycles is ques ionable.Wepe o m a h oughou anal-
ysis o hese species using se e al densi y unc ional app ox-
ima ions (DFAs) and a ious ools o analyze he a oma ici y,
p o iding compelling e idence ha he conclusions a e highly
sensi i e o he le el o calcula ion employed. In pa icula ,
[*] D .I.Casademon -Reig, R. Gue e o-A il8s, D .E.Ramos-Co doba,
D .M.To en -Suca a , D .E.Ma i o
Donos ia In e na ional Physics Cen e (DIPC)
20018 Donos ia,Euskadi (Spain)
E-mail:eloy[email p o ec ed]
[email p o ec ed]m
[email p o ec ed]
D .I.Casademon -Reig, D .E.Ramos-Co doba
Polime o e a Ma e ial Au e a uak:Fisika, Kimika e a Teknologia,
Kimika Fakul a ea,Euskal He iko Unibe si a ea UPV/EHU
P.K. 1072, 20080 Donos ia, Euskadi (Spain)
R. Gue e o-A il8s
Cen o de F&sica de Ma e iales, CFM-MPC CSIC-UPV/EHU
20018 Donos ia,Euskadi (Spain)
D .M.To en -Suca a , D .E.Ma i o
Ike basque, Basque Founda ion o Science
Plaza Euskadi 5, 48009 Bilbao, Euskadi (Spain)
D .M.To en -Suca a
Depa men o O ganic Chemis y I, Uni e sidad del Pais Vasco/
Euskal He iko Unibe si a ea (UPV/EHU)
20018 Donos ia,Euskadi (Spain)
[**] Ap e ious e sion o his manusc ip has been deposi ed on
ap ep in se e (h ps://doi.o g/10.26434/chem xi .14035919).
Suppo ing in o ma ion and he ORCID iden i ica ion numbe (s) o
he au ho (s) o his a icle can be ound unde :
h ps://doi.o g/10.1002/anie.202108997.
T2021 The Au ho s. Angewand eChemie In e na ional Edi ion
published by Wiley-VCH GmbH. This is an open access a icle unde
he e ms o he C ea i e Commons A ibu ion Non-Comme cial
NoDe i s License, which pe mi s use and dis ibu ion in any
medium, p o ided he o iginal wo k is p ope ly ci ed, he use is non-
comme cialand no modi ica ions o adap a ions a e made.
Figu e 1. S uc u e o c-P6. Fo he nano ing s uc u e wi h he a yl
g oup subs i uen s (o ange) and he encapsula ed empla e (pu ple)
we will use he no a ion c-P6·T6. In Re . [9], hey syn hesized he
compound wi h A =(3,5-bis( ihexylsilyl))phenyl, whe eas he compu-
a ional s udies used A =Ph o c-P6·T6 and A =H o c-P6.
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B3LYP p esen s la ge delocaliza ion e o s ha a i icially
enhance he a oma ici y o c-P66+,whe eas CAM-B3LYP
p o ides an excellen ag eemen wi h he expe imen al da a
a ailable.Th ough ca e ul compu a ional analysis and he
judicious examina ion o he 1H-NMR da a, we conclude ha
c-P66+is no a oma ic.
Addi ionally,wepe o m acomple e elec onic s uc u e
s udy o he ou oxida ion s a es o he nano ing and analyze
he a oma ici y o hese molecules.Bys udying he local
a oma ici y o he six po phy ins ha compose he bel
s uc u e and he conjuga ed linke s ( he bu adiyne agmen s
linking he po phy ins), we iden i y he pa s o he molecule
ha a e esponsible o he absence o he global a oma ic
ing cu en . Finally,wep o ide some hin s ha migh aid in
he syn hesis o la ge a oma ic nano ings.
Resul s and Discussion
Thesyn hesized molecules consis o abel nano ing
s uc u e o six po phy ins wi h a yl g oups and an encapsu-
la ed empla e (c-P6·T6, see Figu e 1). The e,Ande son
e al.[9] compu a ionally analyzed he a oma ici y o he
nano ing s uc u e wi hou he a yl g oups and he empla e
(i.e., c-P6) because he nano ing bel s uc u e is he one
esponsible o he a oma ici y o hese compounds.In his
wo k, we ha e also analyzed he e ec o adding he
encapsula ed empla e and he a yl g oups o he c-P66+
s uc u e.
DFAs wi h alow pe cen age o Ha ee–Fock (HF)
exchange ( ypically,HF[%]!50) a long in e elec onic
anges a e p one o p esen la ge delocaliza ion e o s,[27]
leading o he unphysical o e delocaliza ion o elec ons,
he unde es ima ion o eac ion ba ie s and cha ge- ans e
exci a ion ene gies,[27] he o e es ima ion o he conduc ance
o molecula junc ions,op ical esponses,[28,29] he magne -
izabili y o s ong an ia oma ic molecules,[30] elec on con-
juga ion,[31] and a oma ici y,[32,33] especially in la ge conjuga -
ed mac ocycles.[2,3,34–37] Ande son e al.[9] pe o med B3LYP
(HF[%]=19), M06-2X (HF[%]=54), and wB97X (HF[%] =
0–100) calcula ions wi h he 6-31G* basis se bu mos ly
employed he B3LYP esul s o analyze he a oma ici y o
hese compounds.Weha e pe o med addi ional calcula ions
wi h CAM-B3LYP (HF[%]=19–65) and LC-wHPBE (HF-
[%]=0–100), wbeing 0.1 and 0.2 ( he la ge w, he la ge
HF[%] a long ange). Al hough all me hods gi e quali a-
i ely he same s uc u e o he neu al and he c-P612+
species,c-P64+and c-P66+p esen signi ican ly di e en
geome ies depending on he amoun o long- ange HF
exchange p esen in he DFA. While CAM-B3LYP,M06-2X,
and LC-wHPBE(w=0.2) gi e aless symme ic s uc u e o
c-P66+,B3LYP and LC-wHPBE(w=0.1) yield asymme ic
a oma ic species (see Tables 1and S2). The i s g oup o
DFAs has ala ge pe cen age o HF exchange a long ange,
indica ing ha he la e DFAs may be su e ing om
delocaliza ion e o s.This is u he ein o ced by single-
poin DLPNO-CCSD(T)/de -SVP-C calcula ions ha a i-
bu e much lowe ene gy o he less symme ic c-P66+
s uc u es o M06-2X and CAM-B3LYPgeome ies com-
pa ed o he B3LYP one (see Table 2), and he ac ha CAM-
B3LYP iden i ies he symme ic s uc u e as a ansi ion s a e
(TS) connec ing o equi alen minimal s uc u es wi h non-
equi alen linke s (see Figu e 2). Indeed, he B3LYP minimal
geome y has ag ea esemblance wi h he geome y o his
TS (see Table 1). Thesi ua ion is eminiscen o he e o
commi ed by B3LYP in he po en ial ene gy su ace o
ex ended po phy ins,[34] and cas s ashadow o doub o e he
conclusions ob ained using his B3LYP geome y.[9] In he
case o c-P64+,single-poin DLPNO-CCSD(T)/de -SVP-C
calcula ions iden i y he B3LYP geome y as he lowes -lying
one.Al hough, in he la e case, he ene gy di e ences a e so
Table 1: Compa ison o CAM-B3LYP and M06-2X g ound s a e geo-
me ies agains he B3LYP one.[a]
Species RMSD(CAM-B3LYP) RMSD (M06-2X)
c-P6 0.05 0.04
c-P64+0.66 0.20
c-P66+0.22 0.21
c-P612+0.04 0.04
TS c-P66+0.06 0.07
[a] All oo mean squa e de ia ions (RMSD)[26] a e gi en wi h espec o
he B3LYP minimum.TSc-P66+co esponds o he ansi ion s a e o c-
P66+connec ing wo ene gy minima (see Figu e 2).
Table 2: c-P64+and c-P66+DLPNO-CC/De -SVP/C ela i e ene gy alues
wi h espec o he co esponding lowes alue.[a]
Species Op imiza ion Geome y DECCSD DECCSD(T)
c-P64+B3LYP min 0.0 0.0
CAM-B3LYPmin @5.2 7.8
M06-2X min @1.8 5.5
c-P66+M06-2X min 0.0 0.0
B3LYP min 81.9 68.4
CAM-B3LYPmin 8.3 10.9
CAM-B3LYPTS32.4 25.0
M06-2X TS 28.2 18.8
[a] All T1diagnos ic[38] alues a e below 0.017. DFTcalcula ions employed
he 6-31G* basis se . Ene gy in kcalmol@1.
Figu e 2. Ske ch o he po en ial ene gy su ace o c-P66+a ound he
ene gy minimum as desc ibed by di e en DFAs.
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small wi h espec o o he DFAs (2–8 kcalmol@1), ha one
canno unequi ocally d aw any conclusion abou he geo-
me ies (see below o an assessmen o he a oma ici y o c-
P64+calcula ed wi h di e en geome ies).
Thus a ,weha e analyzed he isola ed nano ing model.
A he B3LYP le el o heo y, he addi ion o he empla e
and he a yl g oups b eaks he D6hsymme y ha was
o iginally p edic ed by he naked nano ing,p o iding an
o e all geome y ha is much close o he CAM-B3LYP C3h
geome y.Fo B3LYP,M06-2X, and CAM-B3LYPgeome-
ies, he oo mean squa e de ia ions (RSMD) o he 1H-
NMR chemical shi s o a ious ele an hyd ogen a oms a e
collec ed in Table 3(see Figu e S1). Rep oducing expe imen-
al 1H-NMR alues is a e y challenging compu a ional ask
because hey depend no only on he moleculeQsgeome y bu
also on he sol en and he empe a u e.[39] Howe e ,CAM-
B3LYP geome y p o ides he closes ag eemen wi h he
expe imen o all compounds es ed, whe eas B3LYP’s
p o ides he wo s ag eemen (see Table 3), especially in
he case c-P66+.Hence,wecan sa ely conclude ha CAM-
B3LYP geome ies and he 1H-NMR o c-P6, c-P66+,and c-
P612+con o m o he expe imen al da a, whe eas,in he case
o c-P64+, he e a e la ge disc epancies be ween he expe -
imen al da a and all he examined DFAs.Asweshall see in
he ollowing sec ions,ob aining he igh geome y is c ucial
o co ec ly assess he a oma ici y o c-P66+.He ea e ,unless
o he wise explici ly indica ed, we will e e o he esul s
ob ained om CAM-B3LYPgeome ies.
We ocus now on he local a oma ici y o he po phy ins,
which is assessed by s udying he ci cula conjuga ion pa h-
ways ha go h ough C@Co C
@Nbonds a ound each
po phy in. Thepa hway going h ough he C@Nbonds o he
imine g oup is labeled as “i”, whe eas he one ollowing he
C@Cbonds o he imine g oup is labeled as “o”. The e a e 16
pa hways o each po phy in bu some o hem a e equi alen
by symme y.Weemploy ACID plo s[40] as amagne ic
c i e ion o a oma ici y,aswellasse e al elec on-delocali-
za ion measu es o a oma ici y.[41]
In Table 4, he esul s o all he possible pa hways in he
po phy ins o he neu al species a e collec ed. Thedelocal-
iza ion indices[47] do no show signi ican di e ences be ween
neighbo ing C@Nand C@Cbonds in he imine g oup,
indica ing no clea p e e en ial pa hway in he po phy ins o
c-P6 (see Figu e S3). AVmin,[46] which measu es he leas
delocalized agmen along he pa hway,does no ind
signi ican di e ences among he pa hs ei he ,a ac which
is u he con i med by he ACID plo o Figu e 3a.O he
a oma ici y measu es like FLU[42,43] o HOMA[44] ind some
di e ences be ween he pa hways,bu one should keep in
mind ha , unlike AVmin, hese indices ailed o iden i y he
mos a oma ic pa hway in simple po phy ins.[3,35]
In Table 5, we collec he esul s o he mos a oma ic
pa hway o he po phy ins o all he oxida ion s a es o he
nano ing acco ding o di e en a oma ici y desc ip o s.All
he indices ind ha he po phy ins o c-P6 a e less a oma ic
han hose o po phin (see Table S6) bu a oma ic none he-
less.Al hough he indices do no ag ee on he mos a oma ic
pa hway o he po phy ins (see Tables S7 and S9), he e is
Table 3: Selec ed 1H-NMR chemicalshi di e ences (in ppm).[a]
Me hod da a c-P6·T6 c-P6·T64+c-P6·T66+c-P6·T612+
CAM-B3LYP b-a2.40 0.09 @0.79 @2.15
o’-o 0.09 0.41 @0.19 @0.91
a-a emp @6.34 @1.92 @0.97 1.88
b-b emp @2.54 @0.44 @0.36 1.13
RMSD 0.16 –1.35 0.45
B3LYP b-a1.95 @12.75 0.99 @4.37
o’-o 0.31 36.36 @7.23 @2.67
a-a emp @5.34 60.43 @12.26 5.63
b-b emp @1.97 49.10 @9.85 2.68
RMSD 0.30 –5.36 1.41
Expe imen al b-a2.58 @2.80 @0.44 @2.48
o’-o 0.26 – @1.87 @0.74
a-a emp @6.31 14.16 @2.83 2.77
b-b emp @2.34 12.57 @2.06 1.50
[a] RMSD a e based on nine 1H-NMR di e ences wi h espec o he
expe imen al da a a ailable in Re . [9].Da a o c-P6·T64+is aken om
Re . [13]. a emp and b emp a e he co esponding da a calcula ed on he
isola ed empla e (see Figu e 1). See Figu e S1 and Tables S3 and S4 o
compu a ional de ails, p o on labels, and all 1H-NMR alues.
Table 4: A oma ici y indices o he di e en pa hways wi hin he
po phy ins o c-P6 calcula ed a he CAM-B3LYP/6-31G* le el o heo y.[a]
Pa hway FLU[42,43] BOA HOMA[44] BLA AV1245[45] jAVmin j[46]
oooo 0.023 0.235 0.658 0.050 1.64 0.57
iiii 0.007 0.071 0.927 0.017 0.92 0.52
ioio (2) 0.016 0.162 0.778 0.036 1.32 0.52
iiio (4) 0.012 0.119 0.848 0.027 1.13 0.52
iioo (2) 0.016 0.162 0.778 0.036 1.32 0.52
iooi (2) 0.016 0.162 0.778 0.036 1.32 0.52
oooi (4) 0.020 0.200 0.715 0.043 1.49 0.52
[a] The numbe in b acke s indica es he numbe o equi alen pa hways.
Figu e 3. ACID isosu ace plo s (isocon ou alue 0.06) o a) c-P6,
b) c-P64+,c)c-P66+,and d) c-P612+a he CAM-B3LYP/6-31G* le el o
heo y.
Table 5: A oma ici y indices o he mos a oma ic pa hway o po phy -
ins calcula ed a he CAM-B3LYP/6-31G* le el o heo y.
Species FLU HOMA AV1245 jAVmin jACID
c-P6 0.007 0.927 1.64 0.57 A
c-P64+0.016 0.784 1.45 0.32 A
c-P66+0.017 0.760 1.33 0.24 NA
c-P612+0.027 0.426 0.63 0.04 NA/AA
po phin 0.006 0.968 2.16 1.28 A
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aconsensus among he desc ip o s conce ning he a oma ic
cha ac e o he po phy ins in c-P6 and he ac ha c-P64+’s,
c-P66+’s, and c-P612+’spo phy ins a e much less a oma ic han
hose o c-P6. ACID plo s (see Figu e 3) concu wi h hese
esul s,e en hough hey iden i y he po phy ins in c-P64+as
a oma ic.
1H-NMR esul s we e also used by Ande son e al.[9] o
assess he a oma ici y o he po phy ins.Acco ding o he
expe imen (see Table 3), he di e ences be ween he shield-
ing o aand bp o ons o he empla e (see Figu e S1) a e 2.58,
@2.80, @0.44, and @2.48 ppm o c-P6·T6, c-P6·T64+,c-
P6·T66+,and c-P6·T612+, espec i ely.The la e alues a e
associa ed wi h a oma ic,an ia oma ic,non-a oma ic,and
an ia oma ic po phy ins.CAM-B3LYP alues a e 2.40, 0.09,
@0.79, and @2.15 ppm, in good ag eemen wi h he expe -
imen al alues,whe eas he B3LYP alues o c-P6·T64+,c-
P6·T66+,and c-P6·T612+show la ge disc epancies.
Finally,wes udy how he cons i uen pa s o he
compound change upon oxida ion o he nano ing.Weha e
pe o med an e ec i e oxida ion s a e (EOS)[48,49] analysis o
h ee di e en agmen s o he nano ing: he zinc a oms
(Zn), he po phy ins (P), and he linke s (L). Theca bon
sha ed by he po phy in and he linke s is assigned o he
po phy in. The
esul s o his analysis a e collec ed in Table 6.
In all species, he Zn a om has an EOS o +2, indica ing ha
he oxidized elec ons ne e come om he Zn a om. In c-
P64+, he elec ons a e sub ac ed om he bu adiyne linke s,
dis o ing he o e all symme y ha he linke s had in he
neu al species.In e es ingly,incompounds wi h highe
oxida ion s a es,c-P66+and c-P612+, he elec ons a e sub-
ac ed om he po phy ins, es o ing he symme y o he
neu al species.These esul s ag ee wi h he dec ease o local
a oma ici y we ha e ound wi h he a oma ici y desc ip o s
and help o explain he loss o symme y in he case o c-P64+.
Now,weassess he global a oma ic cha ac e o he
nano ing s uc u e,i.e., we ocus on inding aclosed con-
juga ion pa hway ha goes a ound he nano ing bel . This
pa hway in ol es bo h he po phy ins and he linke s ha
b idge hem. Since we ha e al eady s udied he a oma ici y o
he po phy ins,we i s ocus on he bu adiyne linke s and,
a e wa d, we analyze he whole conjuga ed pa hway in ol -
ing bo h s uc u es.
In Table 7, we collec he MCI[50] o he six ca bons ha
compose each linke .MCI alues measu e he ex en o
elec on delocaliza ion along he ca bon a oms in he link-
e ,[51] which is a he small o c-P6 and c-P612+,indica ing ha
he linke s canno con ibu e o o ming acomple ely delo-
calized ci cui along he nano ing bel (hence,c-P6 and c-
P612+canno be conside ed a oma ic molecules). MCI alues
o c-P64+and c-P66+exhibi an al e na ed pa e n, i.e., an
une en delocaliza ion o he linke s,which also p ecludes he
appea ance o aglobal conjuga ed pa hway ha can be
connec ed wi h a oma ici y.This pic u e is co obo a ed by
he ACID plo s shown in Figu e 4, whe e we can see
disconnec ed sec ions a ound he posi ion o he linke s o
all oxida ion s a es.F om his analysis and he local a oma-
ici y o he po phy ins,wecan cons uc he schema ic model
o he ou nano ingsQa oma ici y ha we collec in he i s
ow o Figu e 5.
Table 6: E ec i e oxida ion S a es (EOS) o se e al agmen s o he
nano ing a he CAM-B3LYP/6-31G* le el o heo y.
Species Zn Po phy ins Linke s
c-P6 +20@2
c-P64++20(@1)W4, (@2)W2
c-P66++2+1@2
c-P612++2+2@2
Table 7: MCI (W1000) alues o he six ca bon a oms ha o m he
linke b idging wo po phy ins.
Species/Linke L1L2L3L4L5L6
c-P6 111111
c-P64+20 4420 44
c-P66+121121 121
c-P612+111111
Figu e 4. ACID isosu ace plo s (isocon ou alue 0.06) o a) c-P6,
b) c-P64+,c)c-P66+,and d) c-P612+.
Figu e 5. The global a oma ic cha ac e o he nano ing om i s
cons i uen pa s acco ding o he op imized geome ies ob ained wi h
di e en DFAs. Full, hal - ull, and emp y ci cles ep esen a oma ic,
weakly a oma ic, and non-a oma ic po phy ins, espec i ely.The elec-
on delocaliza ion in he linke s inc eases om single solid lines (no
delocaliza ion) osolid-dashed lines and, inally,double lines.
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Theglobal a oma ici y o he nano ing can be u he
analyzed using se e al a oma ici y c i e ia ( o u he de ails
see he Suppo ing In o ma ion). We ely he e on AVmin,[46]
which measu es he elec on delocaliza ion along he di e -
en a oma ic pa hways o he nano ing.[2,35] Fo c-P612+,AV
min
is negligible o all he conjuga ion pa hways,clea ly es ab-
lishing he non-a oma ic cha ac e o his molecule.Fo c-P6,
c-P64+,and c-P66+, he alues o AVmin a e negligible o mos
pa hways excep he one ha passes h ough he ni ogen
a oms o imine g oups o each po phy in. In his pa hway,
AVmin is also low bu no negligible,which is eminiscen o
some expanded po phy in s uc u es,which we e conside ed
e y weakly a oma ic o an ia oma ic.[35] The e is,howe e ,
an impo an di e ence conce ning he la e case:in
a oma ic expanded po phy ins, he minimal alue o elec on
delocaliza ion was achie ed wice o h ee imes du ing he
whole pa hway (see Figu e S4), whe eas in he case o c-P64+
and c-P66+ he e a e mul iple (o e wen y) low-delocaliza-
ion agmen s,aswe can see in he delocaliza ion p o ile o
Figu e 6. Fo his eason, all he nano ings in he p esen s udy
a e conside ed non-a oma ic,acco ding o AVmin.In e es -
ingly, o c-P64+,c-P66+,and c-P612+, he as majo i y o hese
disconnec ion poin s occu in he ansi ion om he po phy-
in o he linke ,whe eas o c-P6, he leas delocalized
agmen co esponds o an in e nal agmen inside he
po phy in. ACID con i ms he mos a oma ic pa hway
indica ed by AVmin,and i s discon inuous isosu aces (see
Figu e 4) also sugges ha he molecules a e non-a oma ic,
especially c-P66+, o which la ge discon inui ies also occu in
he icini y o he linke s.Finally,weha e pe o med wo-
dimensional NICS p o iles[52,53] and collec ed hem in l.h.s.o
Figu e 7. In all cases, he alues o he NICS inside and
ou side he nano ing bel a e e y close o ze o, u he
con i ming he global non-a oma ic cha ac e o hese
molecules.
Figu e 5, p o ides aquali a i e compa ison o he a oma-
ici y analyses pe o med on CAM-B3LYP(o M06-2X) and
B3LYP geome ies.The e a e no signi ican di e ences o c-
P6 and c-P612+,asexpec ed om he simila i y o hese
geome ies ega dless o he DFAemployed o he op imi-
za ion. In ac , only o c-P66+,weob ain acomple ely
di e en pic u e o he a oma ici y om di e en me hods.
Thela ge nega i e numbe o he wo-dimensional NICS
p o ile in he icini y o he nano ing cen e (see he .h.s.o
Figu e 7) and he con inuous ACID plo s (Figu e S14)
indica e ha he B3LYP geome y is globally a oma ic.This
is u he co obo a ed by he la ge AVmin alue and, mos
impo an ly,by he 1245-index dis ibu ion p o iles (Fig-
Figu e 6. The 1245-index dis ibu ion along he mos a oma ic pa h.
Figu e 7. NICS(0)iso[54] g id plo s o c-P6, c-P64+,c-P66+,and c-P612+
species om op o bo om, espec i ely.a)–d) co esponding o he
CAM-B3LYP op imized geome ies and e)–h) o he B3LYP ones. See
Figu e S15 and Table S14 o u he de ails o his compu a ion.
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u e 8), whe e we obse e he d as ic educ ion in he numbe
o agmen s wi h alow delocaliza ion. Thecompa ison o he
a oma ici y measu es be ween B3LYP and CAM-B3LYP c-
P64+geome ies also sugges s ha B3LYP o e es ima es he
global an ia oma ici y o his molecule,as he NICS (see
Figu e 7and Table S14) shows ala ge posi i e alue in he
cen e o he ing and he ACID plo s exhibi acon inuous
pa a opic ing cu en (Figu e S14). These esul s align wi h
he ecen esul s o Sundholm and co-wo ke s,which iden i y
CAM-B3LYP as agood me hod o calcula e magne izabil-
i ies[55] and he ac ha B3LYP ends o o e es ima e he
pa amagne ic ing cu en s.[56] On he o he hand, AVmin and
he 1245-index dis ibu ion p o iles (Figu e S8) a e consis en
wi h c-P64+being a a he an ia oma ic o aweakly a oma ic
molecule, ega dless o he geome y.Since he esul s o no
DFAsa is ac o ily con o m o he expe imen al da a, he
esul s o c-P64+should be aken wi h cau ion.
Ande son and co-wo ke sQs onges expe imen al e i-
dence o assess he global a oma ici y o c-P66+comes om
he NMR da a. They s udy he (de)shielding o he ihex-
ylsilyl g oups (see Figu e 1), he o ho p o ons (o and o’)in
he a yl g oups (see Figu e S1), and he shielding di e ence
be ween he a(o b)p o on o he bound empla e and he
ee empla e, Dda=da@da emp (Ddb=db@db emp ).[13] The o me
da a canno be s udied in he p esen pape due o he
compu a ional limi a ions ha pose such la ge s uc u e.
Howe e ,wecan analyze a,b,and o ho p o ons.The B3LYP
geome y inds ha do’@dois @7.23 ppm, whe eas CAM-
B3LYP and M06-2X esul s a e @0.19 ppm and @0.36 ppm,
espec i ely,which a e in close ag eemen wi h he expe i-
men ,[9] 1.87 ppm (see Tables 3and S3). TheCAM-B3LYP
alues o Ddaand Ddba e in much be e ag eemen wi h he
expe imen al da a han he B3LYP ones.Rikhaus e al.[13]
a gue ha Dda<0and Ddb<0a e an indica ion o he
p esence o aglobal a oma ic cu en (while he opposi e is
e idence o an an ia oma ic cu en ). Howe e , his would
indica e no only ha c-P6·T66+is globally a oma ic,bu also
ha c-P6·T6 is e en mo e a oma ic han he o me ,which is
no suppo ed by any o he expe imen al o compu a ional
da a. We ha e also calcula ed Ddaand Ddbin abound
empla e in which we ha e elimina ed he alleged cu en (by
emo ing he b idging bu adiyne linke s), and we ha e ound
nega i e and posi i e Ddaand Ddb,which would suppo he
p esence o a ing cu en e en in he absence o connec i i y
among he po phy ins (see Suppo ing In o ma ion). These
esul s b ing abou wo impo an conclusions.Fi s o all, i
ein o ces he idea ha CAM-B3LYP(o M06-2X) a e mo e
adequa e me hods o ob ain he geome y o po en ial
a oma ic molecules han B3LYP,which incu s la ge delocal-
iza ion e o s.Second, h ough a ious a oma ici y p obes,we
ha e shown ha he B3LYP geome y o c-P66+co esponds
o aqui e a oma ic molecule wi h do’@[email protected] ppm, and
[email protected] ppm. Hence,i he co esponding expe imen al
alues a e only @1.87 ppm and @2.83 ppm, espec i ely, his is
clea ly sugges ing ha c-P6·T66+is ei he e y weakly
a oma ic o non-a oma ic,as he CAM-B3LYP esul s
indica e.This esul is u he ein o ced by a ecen inding[57]
ha he expe imen al a oma ic s abiliza ion ene gy o c-
P6·T66+is ca. 1.2 kcalmol@1,which is ela i ely small o an
a oma ic molecule.
Conclusion
We ha e p o ided compelling e idence ha he B3LYP
desc ip ion o c-P66+su e s om se e e delocaliza ion e o s
ha esul in he o e es ima ion o he a oma ici y o his
species.This is ye ano he p oo [2,3,31–35] ha DFAs wi h alow
pe cen age o long- ange HF exchange should no be used o
analyze a oma ic compounds,especially la ge conjuga ed
ci cui s.Compu a ional esul s a he CAM-B3LYP le el
con o m wi h he expe imen al da a o c-P6, c-P66+,and c-
P612+,whe eas, o c-P64+,none o he DFAs we ha e
employed p o ides asa is ac o y ag eemen wi h he expe i-
men . Th ough ca e ul compu a ional analysis and he judi-
cious examina ion o he 1H-NMR da a, we conclude ha c-
P66+is no a oma ic and ha 1H-NMR da a canno be used o
unequi ocally assess he a oma ici y o his species.Hence,
none o he la ge nano ings s udied can be conside ed
a oma ic,and he ques o la ge a oma ic nano ings should
be con inued. Al hough an enhanced conjuga ion o some
pa hways passing h ough he po phy ins would help o
inc ease he global a oma ici y o hese nano ings,ou esul s
show ha he main eason behind he absence o an a oma ic
ing cu en in hese nano ings is he low delocaliza ion in he
ansi ion om he po phy ins o he b idging bu adiyne
linke s,which dis up s he o e all conjuga ed ci cui .
Acknowledgemen s
This wo k has been suppo ed by g an s om he Spanish
go e nmen MICINN (PGC2018-098212-B-C21, PID2019-
104772GB-I00, EUR2019-103825, PID2019-105488GB-I00,
and PCI2019-103657), Dipu acilnFo al de Gipuzkoa (2019-
CIEN-000092-01), and Gobie no Vasco (IT1346-19, IT1254-
19, PRE_2016_1_0159, and PIBA19-0004). E.R.C.acknowl-
edges unding om he Juan de la Cie a p og am IJCI-2017-
34658.
Figu e 8. The 1245-index dis ibu ion along he mos a oma ic pa h o
c-P6·T66+.See Figu e 6 oloca e he poin s o he molecule ep esen -
ed in he x-axis.
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Theau ho s decla e no con lic o in e es .
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Manusc ip ecei ed:July 6, 2021
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