Communication of molecular fluorophores with other photoluminescence centres in carbon dots

Nanoscale PAPER Ci e his: Nanoscale, 2023, 15, 4022 Recei ed 16 h Sep embe 2022, Accep ed 30 h Janua y 2023 DOI: 10.1039/d2n 05114a sc.li/nanoscale Communica ion o molecula fluo opho es wi h o he pho oluminescence cen es in ca bon do s† Michal Lange , a,b LukášZd ažil, a Mi osla Med eď* a,c and Michal O yepka * a,d The es ablishmen o s uc u e-pho oluminescence (PL) ela ionships emains an ul ima e challenge in he field o ca bon do s (CDs). I is now commonly unde s ood ha a ious s uc u al domains may e ol e du ing he p epa a ion o CDs; none heless, we a e s ill a om cap u ing he specific ea u es ha de e mine he o e all PL o CDs. Al hough he co e, su ace and molecula s a es a e usually conside ed he h ee main sou ces o PL, i is no known o which ex en hey in e ac and/o affec one ano he . Expec edly, he communica ion be ween he diffe en PL cen es depends on he mu ual a angemen and he ype o linking. To gain insigh s in o such a communica ion, ime-dependen densi y unc ional heo y (TD-DFT) calcula ions we e pe o med o se e al (N-doped/O- unc ionalized) polya oma ic hyd oca bons (PAHs) as ep esen a i e models o he co e/su aces PL s a es and he p o o ypical mole- cula fluo opho e (MF) 5-oxo-1,2,3,5- e ahyd oimidazo-[1,2-α]-py idine-7-ca boxylic acid (IPCA), con- side ing diffe en in e ac ion modes, namely hyd ogen bonded and s acked complexes as well as co- alen ly bonded and used s uc u es. Ou esul s e ealed ha each o he s udied a angemen s in some way suppo ed he communica ion be ween he PL cen es. The deac i a ion pa hways ypically in ol e mul iple cha ge and ene gy ans e e en s ha can p omo e he o ma ion o cha ge sepa a ed s a es and/o lead o he ac i a ion o o he PL cen es in CDs. Depending on he a angemen , he doping pa e n and su ace unc ionaliza ion, bo h he CD co e and he MF can ac as an elec on dono o accep o , which could help o design CDs wi h desi able hole–elec on su ace/co e cha ac e is ics. In oduc ion Ca bon do s (CDs) ep esen a highly a ac i e class o ze o- dimensional ca bon nanoallo opes. Since hei disco e y by Xu e al., 1 he CDs ha e been p aised as low-cos , biocompa ible, chemically s able, wa e soluble nanosys ems wi h ou s anding op ical and elec ical p ope ies, such as in ense pho o- luminescence (PL), high esis ance o pho obleaching, high elec- on mobili y, and pho o-induced elec on ans e . 2,3 These p o- pe ies endow CDs wi h applica ions anging om pho oca aly- sis, sensing, and imaging up o ligh -emi ing diodes. 4–9 Gene ally, CDs a e de ined as quasi-sphe ical objec s wi h a diame e below 10 nm possessing a mul ilaye g aphi e co e and oxygen and/o ni ogen unc ional g oups on he CD shell. 10 Al hough CDs a e o en ca ego ized in o h ee ypes, i.e., g aphene quan um do s (GQDs), ca bon nanodo s (CNDs), and ca bonized polyme ic do s (CPDs), hei s uc u al com- plexi y is as . This s ems om miscellaneous syn he ic p o- cedu es, as small changes in eac ion condi ions o p ecu so s can lead o diffe en CDs. 11–14 To achie e be e con ol o e he p ope ies o CDs o speci ic applica ions, he ela ion- ships be ween he s uc u e and PL mechanisms o CDs need o be ully unde s ood. CDs exhibi mul i-cen e emission wi h h ee sou ces being used o explain he PL o igins o CDs, i.e., co e s a es due o ca bon sp 2 domains, su ace s a es s emming om su ace chemical g oups, and molecula s a es due o he p esence o molecula luo opho es (MFs). 15–18 Va ious s uc u al domains wi hin CDs may con ibu e o he PL o CDs, and hey can e en co-ope a e and/o in luence each o he . 19 Thus, many p ocesses such as he cha ge ans e (CT), ene gy ans e (ET), adia ionless de-exci a ions, ( e e se) in e -sys em c oss- ing (ISC), and in ol emen o ap s a es may be expec ed o occu upon pho oexci a ion o CDs (Fig. S5†). Ne e heless, †Elec onic supplemen a y in o ma ion (ESI) a ailable. See DOI: h ps://doi.o g/ 10.1039/d2n 05114a a Regional Cen e o Ad anced Technologies and Ma e ials, Czech Ad anced Technology and Resea ch Ins i u e (CATRIN), Palacký Uni e si y Olomouc, Šlech i elů 241/27, 783 71 Olomouc, Czech Republic. E-mail: mi osla .med [email p o ec ed], [email p o ec ed] b Chemical and Biological Sys ems Simula ion Lab, Cen e o New Technologies Uni e si y o Wa saw, 2c Banacha S ee , 02-097 Wa szawa, Poland c Depa men o Chemis y, Facul y o Na u al Sciences, Ma ej Bel Uni e si y, Tajo ského 40, 974 01 Banská Bys ica, Slo ak Republic d IT4Inno a ions, VŠB-Technical Uni e si y o Os a a, 17. lis opadu 2172/15, 708 00 Os a a-Po uba, Czech Republic 4022 |Nanoscale,2023,15,4022–4032 This jou nal is © The Royal Socie y o Chemis y 2023 Open Access A icle. Published on 31 Janua y 2023. Downloaded on 11/20/2023 12:31:33 PM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online View Jou nal | View Issue despi e all he effo s and acqui ed da a, he clea link be ween a pa icula s uc u al ea u e and he obse ed PL signal has no been es ablished ye . Compu a ional chemis y ools a e e y help ul in elucida - ing ela ionships be ween he s uc u e and PL p ope ies o molecula sys ems. The heo e ical s udies ocusing on he in e play be ween a ious PL cen es in he con ex o CDs a e, howe e , e y limi ed. 20,21 Conce ning he molecula s a es, 5-oxo-1,2,3,5- e ahyd oimidazo-[1,2-α]-py idine-7-ca boxylic acid (IPCA) has been iden i ied as a p o o ypical MF in CDs. 22 The op ical p ope ies o IPCA monome and dime ha e been heo e ically s udied in gas and aqueous sol en , 23 and also as a non-co alen ly bonded dime in he model o CD by QM/ MM. 24 None heless, nei he expe imen s no modelling eally p o ided any di ec insigh in o he communica ion o he molecula s a es s emming om he p esence o IPCA wi h o he s uc u al mo i s in CDs. No ully esol ed s uc u al o ganiza ion o MFs wi hin CDs con ibu es o his conun- d um. Fo example, ci ic-acid based luo opho e moie ies ha e been epo ed as a ee- loa ing by-p oduc o CDs p epa- a ion, 25 bu also as being p esen in he CD in e io 26 as well as CD ex e io , 27 o e en co alen ly bonded o he CD su ace, 28 and hese possible scena ios e y likely depend on syn he ic condi ions. 29 He e, we desc ibe he PL p ope ies o a se ies o co e/ su ace/MF models in ol ing a p o o ypical MF IPCA in a ious chemical and s uc u al con ex wi hin CDs. In pa icu- la , ou models co e all plausible ypes o s uc u al a ange- men s (H-bonded, s acked, co alen ly bonded, and used sys ems) o IPCA and a py ene-like polya oma ic hyd oca bon (PAH) molecule ep esen ing he small-sized co e o CDs. Ou esul s show ha he in e play be ween hese PL cen es may no only in oduce new peaks in he abso p ion spec a o he complex (e.g., in co alen ly bonded sys ems), bu many new da k s a es eme ge, which can come o play du ing de-exci- a ion p ocesses. Also, depending on he s uc u al o ganiz- a ion o IPCA and PAH uni s, plausible CT and ET e en s be ween he molecula and co e s a es along he in e nal in e - sion de-exci a ion cascade we e iden i ied, which can lead o he emission om a PL cen e (e.g., co e) diffe en om he one pho o-ac i a ed du ing abso p ion (e.g., IPCA). Expe imen al Models Ou s udied s uc u al domains can be so ed in o ou g oups (Fig. 1), namely H-bonded and s acked complexes, co alen ly single-bonded sys ems, and used sys ems. All model sys ems we e cons uc ed om one p o o ypical MF, IPCA, and one PAH molecule, which ep esen s a CD co e (Fig. 1, Fig. S1†). These models co e he main s uc u al ypes, which can be p esen and co-ope a e in he o e all PL o he CDs. Le us no e ha he used s uc u es can also be conside ed as models gi ing ise o he su ace PL s a es. Besides a pa en py ene molecule (model A; see Fig. S1a†), CD co e models con aining wo inne -la ice g aphi ic ni o- gens (g aphi ic-N-co e models B, D, and F) and wo g aphi ic- edge ni ogens (g aphi ic-N-edge models C and G) we e con- side ed (Fig. S1a†). As CDs usually possess oxygen-con aining unc ional g oups on hei su ace and/o edges, some PAHs we e unc ionalized wi h ei he wo oxo-g oups (models D and E) o one ca boxylic g oup (models F and G). In he model E, he g aphi ic-edge doping was eplaced by wo g aphi ic-co e ni ogens in he same ing (g aphi ic-N-co e2), as we only con- side ed Kekulé s uc u es. To assess he co e-size effec s, co- alen ly bonded as well as s acked complexes con aining an N-doped co onene moie y we e also conside ed (Fig. S15†). Me hods To examine he effec s o a ious binding modes on he na u e o elec onic ansi ions in CD/MF sys ems, he lowes exci ed s a es o coupled sys ems we e ho oughly analysed in e ms o he e ical (de-)exci a ion ene gies and he co esponding oscilla o s eng hs as well as in e ms o elec on densi y diffe ence (EDD) plo s and na u al ansi ion o bi als (NTOs). The densi y unc ional heo y (DFT) and ime-dependen densi y unc ional heo y (TD-DFT) 30 calcula ions we e pe - o med by applying he Coulomb-a enua ing h ee-pa ame e Becke, Lee–Yang–Pa (CAM-B3LYP) 31,32 unc ional including he D3 co ec ion o accoun o dispe sion in e ac ions 33 in combina ion wi h he de 2-TZVP 34 basis se . All calcula ions we e pe o med o hyd a ed sys ems, employing he implici uni e sal sol a ion model based on solu e elec on densi y (SMD), 35 and using he Gaussian 16 ( e ision B.01). 36 The s uc u es we e ende ed in PyMOL 37 and Chemc a . 38 To simula e abso p ion spec a, he g ound s a e (GS) geo- me y o all he models (Fig. S1†) was i s op imized wi hou any symme y cons ain s. All he op imized geome ies we e e i ied o be ue minima on he po en ial ene gy su ace by he absence o imagina y equencies in he ha monic ib a ional analysis. The elec onic e ical exci a ion ene gies (VEEs) we e calcula ed wi hin he TD-DFT amewo k using he linea esponse (LR) as well as co ec ed linea esponse (cLR) app oaches, 39–43 wi h he i s hi y single s a es aken in o conside a ion in he o me . Fu he mo e, LR-TD-DFT cal- cula ions o en lowes single s and iple exci a ions we e pe - o med, on he GS geome ies, o judge on he easibili y o ISC in model s uc u es. I should be no ed ha he e alua ion o adiaba ic single – iple ene gy gaps (ΔE ST ) was no achie - able o all sys ems due o con e gence p oblems (using he applied me hod) du ing geome y op imiza ions o iple exci ed s a e s uc u es. Fo he calcula ion o adia i e de-exci a ions, Kasha emis- sions om he S 1 s a e we e conside ed. The S 1 geome y was i s op imized wi h he de 2-SVP basis se , ollowed by calcu- la ion o emission ene gies wi h he de 2-TZVP basis se apply- ing he equilib ium sol a ion egime o he ES calcula ions and nonequilib ium sol a ion o he subsequen calcula ion o he GS. Nanoscale Pape This jou nal is © The Royal Socie y o Chemis y 2023 Nanoscale,2023,15,4022–4032 | 4023 Open Access A icle. Published on 31 Janua y 2023. Downloaded on 11/20/2023 12:31:33 PM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online CT and ET analyses we e pe o med based on he NTOs ha we e ende ed in Chemc a ( e sion 1.8) and elec on densi y diffe ences (EDDs) displayed in GaussView ( e sion 5.0). 44 The calcula ions o o al coupling o elec onic ene gy ans e (EET) we e pe o med using TD-DFT as implemen ed in Gaussian 16, whe e sol en effec s we e in oduced using he SMD ca i y o he whole sys em; 45,46 ES calcula ions we e pe o med on each agmen , and all he couplings among all he esul ing s a es we e compu ed; and ONIOM-like 47 link- a om inpu in o ma ion o cap he agmen s was used o ou models bonded h ough a single co alen bond in EET calcula ions. Resul s and discussion Fi s , we desc ibe he changes in abso p ion and emission o CDs due o he o ma ion o he PAH/IPCA complexes (Fig. 1). In he second pa , we demons a e how a pa icula bonding ype and/o speci ic s uc u al a angemen o IPCA and PAH can affec he de-exci a ion p ocesses assuming he pho o-ac i- a ion o he sys em by a 350 nm sou ce o ligh , i.e., in he egion o he abso p ion maximum o IPCA. The analysis o he op ical p ope ies o isola ed molecules om which we cons uc ed ou models o es ablish s uc u e-PL ela ionships in CDs and ace he communica ion be ween he co e/su ace and molecula s a es is de ailed in he ESI.† Changes in abso p ion spec a In he H-bonded sys ems, he in e ac ion o bo h IPCA and PAH uni s wi h ligh emains p ac ically independen o each o he . This means ha he o ma ion o H-bonded complexes does no gi e ise o any signi ican new peaks in he CDs abso p ion spec a (Fig. 2a and b), e en hough he on ie o bi al analysis (Fig. S1b and S7†) sugges s a possible CT exci- a ion om he PAH uni o IPCA. Indeed, a CT π–π * ansi ion (s a e S 4 , 401 nm) om PAH o IPCA wi h a a he small in en- si y ( = 0.026) due o a small o e lap o he in ol ed MOs was obse ed in ou COOH_co e model (Tables S11 and S12†). A simila , excep being da k, CT s a e (S 3 ,λ max = 371 nm, = 0.002) was obse ed o he COOH_edge model. The s acking a angemen o PAHs and IPCA opens new abso p ion channels in CDs. No ably highe ene gy o he highes occupied molecula o bi al (HOMO) in N-doped PAH uni s and sligh ly lowe ene gy o he lowes unoccupied mole- cula o bi al (LUMO) in IPCA (Fig. S1†) indica e he plausibili y o low-lying CT exci a ions om N-doped py ene o IPCA, as demons a ed in s acked_co e and s acked_edge models (Fig. 2c, d, S8; Tables S13 and S14†). Howe e , in he model wi h a g aphi ic-N-edge uni (s acked_edge model), he S 0 →S 1 elec onic exci a ion (λ max = 558 nm) exhibi s much s onge CT cha ac e (D index 3.48 Å) om PAH o IPCA (Table S14†) compa ed o s acked_co e complex (D index 1.33 Å). Owing o i s non-ze o oscilla o s eng h ( = 0.021) a new small peak in he isible egion can be obse ed (Fig. 2d). Ne e heless, he in ense abso p ion bands o s acked_co e and s acked_edge (abo e 300 nm) a e due o LEs wi hin he molecula com- ponen s (Tables S13 and S14†), which is in line wi h a good o e lap o he sum spec a wi h hose o sepa a e molecules albei he in ensi y o peaks sligh ly dec eases upon he complex o ma ion (Fig. 2c and d). In oducing O- unc ional g oups in he s acked models (oxo_s acked1_a,oxo_s acked1_b) p ese es he shape o he sum abso p ion spec a o componen s only abo e 380 nm, i.e., he main abso p ion bands a e p edominan ly due o LE ansi ions in his egion (Fig. 2e). The S 0 →S 1 ansi ion is a b igh LE in O-PAH ( = 0.250) peaking a a ound λ max ≈ 453 nm. Below 380 nm, new abso p ion peaks, ele an o pho oexci a ion using a ∼350 nm i adia ion sou ce, eme ge upon he s acking. In oxo_s acked1_a, hese peaks appea due o he hyb idized local and cha ge- ans e (HLCT) S 0 →S 3 ansi ion (λ max ≈360 nm, = 0.049), whe e an elec on is Fig. 1 The schema ic figu e on how CDs ( wo models in he middle), can be o med om PAHs and diffe en in e ac ion sys ems o PAH/IPCA ha we e used as models o ou calcula ions (co esponding chemical s uc u es a e shown in Fig. S1†). Colou ing scheme: blue –ni ogen; ed – oxygen; whi e –hyd ogen; g ey, g een, o ange, beige, cyan, iole , yellow –ca bon. Diffe en colou s o ca bons we e chosen o clea ly show hei loca ion in he models o CDs. Pape Nanoscale 4024 |Nanoscale,2023,15,4022–4032 This jou nal is © The Royal Socie y o Chemis y 2023 Open Access A icle. Published on 31 Janua y 2023. Downloaded on 11/20/2023 12:31:33 PM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online ans e ed om π-o bi al delocalized o e bo h componen s o a π * o bi al localized only on IPCA (Table S16†), and S 0 → S 4,5 (λ max ≈330 nm, = 0.04) ansi ions (Fig. 2e, Table S16†). In oxo_s acked1_b, a new abso p ion peak co esponding o S 0 →S 3 CT exci a ion (PAH →IPCA) a ose a ∼350 nm ( = 0.054, Fig. 2e, Table S17†), o e lapping wi h he LE peak o he IPCA molecule. Ano he albei less b igh CT (IPCA →PAH) exci a ion (λ max ≈335 nm, = 0.027) can be de ec ed in he egion o spec um, whe e ypical exci a ion wa eleng hs a e a ge ed o pho oexci a ion o CDs. The change o he N-doping pa e n in he O- unc ionalized s acked complexes can cause signi ican s uc u al dis o ions (Tables S18 and S19, Fig. S17†). Whe eas oxo_s acked2_b keeps a compac s acked a angemen , oxo_s acked2_a co es- ponds o a pa ially open s acked con igu a ion s abilized by he o ma ion o H-bonding (IPCA–N⋯O–PAH). Consequen ly, he abso p ion spec um o oxo_s acked2_a copies o a la ge ex en hose o he isola ed molecules. On he o he hand, he compac a angemen o oxo_s acked2_b gi es ise o sligh modi ica ions o he band shapes in he 350–400 nm egion (Fig. 2 ) esul ing mainly om he S 0 →S 3 (λ max ≈352 nm, = 0.075) and S 0 →S 5 (λ max ≈343 nm, = 0.041) ansi ions exhibi ing HLCT cha ac e , whe e he elec on is ans e ed om π-o bi al o IPCA o π * -o bi al delocalized o e he complex (Table S19†). Abso p ion spec a o models when he co e/molecula PL cen es CDs a e connec ed wi h an es e bond ( e e ed as es e 1_co e and es e 2_edge models) g ea ly o e lap wi h he abso p ion spec a o he isola ed molecula componen s (Fig. 3a and b). These s uc u al mo i s a e also i al o unde - s anding he CDs PL as hey may occu du ing he syn hesis o CDs be o e he ca boniza ion p ocess is comple ed. No b igh exci a ions wi h CT cha ac e we e obse ed in hese models, which we a ibu e o he wis ed mu ual o ien a ion o bo h uni s (Fig. S11a–h, Tables S20 and S21†) and o he cha ac e o he es e bond, which does no enable efficien elec on delocaliza ion. On he o he hand, an amide bond allows he whole complex being quasi-plana which can signi ican ly affec he elec onic ene gy le els o linked componen s. In he amide1_- co e model, he peak co esponding o LE on IPCA is blue- shi ed by 28 nm compa ed o an isola ed IPCA molecule, as Fig. 2 Abso p ion spec a o non-co alen ly bonded complexes along wi h hose o he sepa a ed molecules which o m he complexes (see mole- cules A–H in Fig. S1†). Fo each spec um, he line spec a (conside ing 30 lowes single s a es) we e con olu ed by a Gaussian unc ion assuming he inhomogeneous b oadening o peaks wi h σ= 20 nm. Nanoscale Pape This jou nal is © The Royal Socie y o Chemis y 2023 Nanoscale,2023,15,4022–4032 | 4025 Open Access A icle. Published on 31 Janua y 2023. Downloaded on 11/20/2023 12:31:33 PM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online he –COOH g oup o IPCA was eplaced by –CONH–g oup (λ max ≈315 nm, = 0.173, Fig. 3c). In amide1_edge, a small pa o elec on densi y is ans e ed om N-doped py ene o a linking amide g oup and o he IPCA uni upon he S 0 →S 2 exci a ion (λ max ≈444 nm, = 0.177), which indica es efficien in e ac ion be ween he wo PL cen es. An addi ional small peak ( = 0.020) can be obse ed a 385 nm due o S 0 →S 3 , which exhibi s CT cha ac e om PAH o IPCA. Due o he e- placemen o –COOH by –CONH–, he LE on IPCA is also blue- shi ed o 316 nm, gi ing ise o an addi ional peak in he abso p ion spec um o amide1_edge model (Fig. 3c). The posi ion o an amide binding g oup co alen ly linking PL s uc u al mo i s inside CDs can also signi ican ly affec he ene gy le els o he sys em. The obse ed changes a e indi ec ly ela ed o he dihed al angle be ween IPCA and py ene uni s (Fig. S11†), as he quasi-plana o ien a ion can lead o a mo e in ense in e ac ion o molecula o bi als o he componen s. Ou esul s co obo a e his hypo hesis, as se e al CT exci a ions we e iden i ied in amide2 and amide3 posi ions o bo h N-doping pa e ns (Tables S22–S27†). Models wi h a g aphi ic-co e uni ,amide2_co e and amide3_- co e, do no abso b ligh in he spec al egion 330–400 nm, simila ly o amide1_co e model (Fig. 3d). The elec on is ans- e ed o he amide g oup and IPCA in S 0 →S 3 in amide2_co e (Table S24†), causing a sligh edshi o he abso p ion maximum. The change o he linking posi ion also in oduces he new peaks a ound 430 nm, which can be desc ibed as (weak) HLCT S 0 →S 4 exci a ion om PAH o IPCA. A s iking diffe ence due o diffe en linking o –CONH–bond was no ed o amide3_edge, in which he abso p ion peak o S 0 →S 1 HLCT ansi ion om PAH o IPCA was blue-shi ed o λ max ≈ 539 nm (Fig. 3e) and a ained a no able oscilla o s eng h ( = 0.122). The o ma ion o used PAH/IPCA sys ems ( used, used_- co e, used_edge models) in CDs would p oduce many new peaks in hei abso p ion spec a (Fig. 3 –h), which may be assigned o he ex ended delocaliza ion effec s and he p es- ence o mul iple b igh CT exci a ions. Con a y o p e iously analysed sys ems, he on ie o bi al analysis sugges s ha he used sys ems should be conside ed mo e as co e/shell sys ems because hei HOMOs and LUMOs a e delocalized o e he en i e model s uc u es (Fig. S14†). In used model, all en lowes b igh exci a ions ha e o some ex en he π–π * cha ac e wi h he π-o bi als delocalized o e he whole sys em (Table S28†), e.g., he S 0 →S 2 ansi ion is a HLCT exci a ion, whe e he elec on densi y p edominan ly ans e s om he whole s uc u e o a PAH pa , howe e , i is less in ense ( = 0.014). Fo he used_co e model, LE on IPCA is now he S 0 → S 4 ansi ion wi h λ max ≈363 nm (Fig. 3g), i.e., ed-shi ed by 21 nm compa ed o IPCA, wi h an inc eased oscilla o s eng h ( = 0.392) in compa ison wi h an isola ed IPCA molecule (Table S29†). The e a e se e al CT exci a ions om PAH o he whole sys em o mos ly o IPCA uni o S 0 →S 3 (λ max ≈ 503 nm, = 0.079). The S 0 →S 5 ansi ion is a HLCT exci a ion om PAH o he whole sys em. The ac ha i is he b igh exci a ion lying in he isible pa o elec omagne ic spec um Fig. 3 Abso p ion spec a o co alen ly bonded complexes along wi h hose o he sepa a ed molecules which o m he complexes (see molecules A–H in Fig. S1†). Fo each spec um, he line spec a (conside ing 30 lowes single s a es) we e con olu ed by a Gaussian unc ion assuming he inhomogeneous b oadening o peaks wi h σ= 20 nm. Pape Nanoscale 4026 |Nanoscale,2023,15,4022–4032 This jou nal is © The Royal Socie y o Chemis y 2023 Open Access A icle. Published on 31 Janua y 2023. Downloaded on 11/20/2023 12:31:33 PM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online (354 nm, = 0.026) offe s he in e es ing egion o a ge he abso p ion in CDs. Conce ning he used_edge model, he S 0 →S 1 exci a ion (λ max ≈592 nm, = 0.122) occu s on he whole model s uc u e, dominan ly on he PAH uni . Again, new exci a ions in compa ison wi h IPCA and N-doped isola ed molecules a e p esen , which co espond o CT exci a ions delocalized o e he whole sys em (Table S30†). These peaks posi ioned a 350, 558 and 511 nm make he used_edge model plausible o he a ionaliza ion o ypical pho o- exci a ion wa eleng hs o CDs. To add ess he impac o he co e size on he abso p ion spec a o he s udied sys ems, ep esen a i e co alen ly bonded as well as s acked complexes con aining an N-doped co onene moie y we e in es iga ed (Fig. S15†). In amide-linked models (amide1_co and amide1_co _edge), b igh CT exci- a ions om PAH o IPCA co esponding in bo h cases o S 0 → S 4 ansi ion a e cen e ed a ound 460 nm (Fig. S16, Tables S31 and S32†), i.e., hey a e ed-shi ed (by ca. 14 and 72 nm, espec i ely) compa ed o py ene-like analogs (Tables S22 and S23†). The S 0 →S 1 e ical exci a ion ene gy is e en mo e ed- shi ed (by 171 nm and 415 nm) o amide1_co and amide1_- co _edge, espec i ely, wi h espec o he smalle -co e sys ems. Fo he s acked complex wi hou O- unc ionaliza ion (s acked_co model), a b igh e CT s a e was ound o N-co onene/IPCA in compa ison o he N-py ene/IPCA coun e - pa , i.e.,S 0 →S 7 ansi ion (λ max ≈320 nm, = 0.030) o N-co onene/IPCA s. S 0 →S 6 ansi ion (λ max ≈317 nm, = 0.004) o N-py ene/IPCA (Tables S13 and S33†). Again, he S 0 →S 1 maximum is ed-shi ed by 156 nm (λ max ≈938 nm) wi h espec o N-py ene/IPCA. In s acked_oxo_co model, he HLCT exci onic ansi ion (S 0 →S 7 ;λ max ≈341 nm) has he oscilla o s eng h wi h he alue = 0.044 (Table S34†), which is simila as in he py ene coun e pa (see oxo_s acked1_a, b). Simila CT s a es we e ound also in s acked_oxo2_co model (S 0 →S 4 ;S 0 →S 6 ;S 0 →S 7 ; Table S35†) and in he s acked complex wi h diffe en N-doping pa e n (s acked_oxo_co 2;S 0 →S 4 ;S 0 →S 5 ;S 0 →S 7 ; Table S36†). In e es ingly, he S 0 →S 1 exci a ion ene gy is ed-shi ed only by 38 nm (λ max ≈491 nm) o he N-co onene/IPCA s acked complex wi h oxo- unc ionali- za ion (s acked_oxo_co model) in compa ison o he oxo_s- acked1_a model (wi h py ene-sized PAH). Despi e a diffe en N-doping pa e n imp in ed in he s acked_oxo_co 2 model, he abso p ion peak co esponding o S 0 →S 1 is no ed- shi ed ou side he Vis egion (λ max ≈518 nm, = 0.051). In gene al, ou esul s indica e ha e en in models wi h a la ge co e han py ene, he o e lap o molecula o bi als o he com- ponen s emains efficien , and new CT s a es a e p esen . Addi ionally, he abso p ion peaks a e ed-shi ed o he la ge co e. To sum up his pa , in he 340–360 nm egion, whe e he isola ed IPCA and i s dime s abso b ligh , o he mul iple abso p ion e en s can occu , hus pho oac i a ing diffe en PL cen es. I was also shown ha no only la ge sp 2 ca bon co e domains bu also he in e ac ion be ween IPCA and PAH uni s in used and amide-bonded sys ems a e likely esponsible o he abso p ion in he isible egion. Mo eo e , i was demon- s a ed ha he elec onic exci a ions wi h CT cha ac e om IPCA o PAH only occu ed in CD co e models unc ionalized wi h oxo-g oups due o he ela i e posi ions o he on ie o bi als isola ed o IPCA and oxo-PAHs. De-exci a ion pa hways The analysis o de-exci a ion pa hways in he s udied models o a ious in e ac ing PAH/IPCA s uc u al domains o CDs p o ides aluable insigh s in o he PL deac i a ion p ocesses occu ing in eal CD samples a e i adia ion. We chose o desc ibe he sequen ial de-exci a ion cascades (S n →S 1 ) a e he pho oexci a ion wi h a 350 nm ene gy sou ce, which is he ypical exci a ion wa eleng h p esumably a ge ing he abso p- ion maxima o MFs such as IPCA. Along he de-exci a ion pa hways based on he NTO analysis, we iden i ied CT/ET p o- cesses be ween he in e ac ing CD componen s (Fig. S5†). Despi e being da k, he CT and ET s a es can play an impo - an ole du ing de-exci a ion dynamic p ocesses, leading o cha ge-sepa a ed exci ons and/o ac i a ion o mul iple PL cen es in CDs. The he e p esen ed de-exci a ion cascades ep- esen al e na i e elaxa ion channels o local de-ac i a ion o IPCA and i s dime s leading o he emission om molecula s a es. 23,24 The o ma ion o H-bonded complexes o IPCA and N-doped PAHs wi hin CDs appea s o p omo e adia ionless channels and hus lowe s he PL QY in CDs. The eason is ha he de-exci a ion cascade b ings he pho oac i a ed H-bonded sys ems down o he S 1 s a e which ge s (a e elaxa ion) oo close o he GS (Fig. 4a and b). In pa icula , in he COOH_co e model, he 350 nm exci a ion sou ce causes popu- la ion o S 6 and S 5 ene gy le els, which a e LEs on IPCA and PAH, espec i ely. Sequen ial in e nal con e sions o S 5 o S 3 in ol e he elec on ans e om PAH o IPCA (S 5 →S 4 ) and e e se CT (S 4 →S 3 ) acco ding o he NTO analysis (Table S11†). The EDD plo o S 1* →S 0* a he elaxed S 1 geo- me y (inse in Fig. 4a) shows he localiza ion o an exci on on PAH, and he p oximi y o S 0 and S 1 ene gy le els in his geo- me y sugges s he non- adia i e de-exci a ion. An analogous pic u e was d awn o he COOH_edge model, wi h one low- lying da k s a e missing in he deac i a ion cascade (Fig. 4b, Table S12†). Simila ly, he s acked complexes o non- unc ionalized N-doped PAHs wi h IPCA endo se non- adia i e channels in CDs, lowe ing he QY (Fig. 4c). The e a e se e al da k CT s a es (e.g.,S 2 and S 6 in s acked_co e model, and S 6 in s acked_edge model) which canno be iden i ied in he abso p ion spec um bu a e impo an in he de-exci a ion p ocesses. A e local exci a ion (S 5 ) on IPCA a 345 nm in he s acked_co e model, S 5 →S 4 ET o he PAH pa o he complex can occu (see sec ion 10 in ESI† o he e alua ions o o al couplings o he EET analysis) al hough he ela i ely la ge ene gy diffe ence (∼1 eV) be ween he wo s a es sugges s a compe i i e pa hway ia di ec emission om he S 5 s a e localized on IPCA in some s acked a angemen s. 23,24 In he case o he S 5 →S 4 in e nal con e sion, ET is ollowed by hyb id local cha ge- ans e (HLCT) o IPCA (S 3 →S 2 ) and HLCT o PAH (S 2 →S 1 ) and Nanoscale Pape This jou nal is © The Royal Socie y o Chemis y 2023 Nanoscale,2023,15,4022–4032 | 4027 Open Access A icle. Published on 31 Janua y 2023. Downloaded on 11/20/2023 12:31:33 PM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online in e nal con e sion o S 1* . Thus, he emission akes place om his HLCT s a e, and i is signi ican ly edshi ed o 1512 nm. Mo eo e , hese HLCT exci a ions ha e almos ze o oscilla o s eng hs, sugges ing low efficiency o adia i e deac i a ion. Wi h he 350 nm sou ce used o he pho oexci a ion, he o - ma ion o an exci on (S 1 →S 5 ) dominan ly localized on PAH pa o he s acked_edge model can be expec ed (Fig. 4d). The ansi ion o om he S 5 s a e o CT S 1 s a e could be desc ibed as a weak ET om PAH o IPCA o h and back, wi h se e al NTOs in ol ed in he ansi ions. Relaxing om S 2 o S 1 , he elec on is ans e ed o IPCA pa . He e, he TD-DFT p e- dic ed ha he S 1 s a e in he elaxed geome y is ene ge ically lowe han GS, which is appa en ly an a e ac o TD-DFT, which is no app op ia e o desc ibing quasi-degene a e s a es and sugges s he occu ence o a conical in e sec ion in his model. The s acked complexes o IPCA wi h O- unc ionalized N-doped PAHs can lead o bo h adia i e and adia ionless de- exci a ion pa hways in CDs depending on he doping pa e n. The exci a ion o he S 3 HLCT s a e in oxo_s acked1_a is ol- lowed by weak ET localizing he exci on on he PAH moie y (Fig. 4e). The S 1 →S 0 emission is b igh ( = 0.558) wi h λ max ≈ 500 nm. I oxo_s acked1_b is pho oexci ed wi h he 350 nm sou ce, S 4 and S 3 s a es become popula ed (Fig. 4 ). The NTO analysis sugges s ha he S 1 ene gy le el is eached ia a sequen ial ET p ocess ( om IPCA o PAH) h ough hole ans- e (S 4 →S 3 ) ollowed by elec on ans e (S 3 →S 2 ). This non- co alen s uc u al domain simila ly emi s he ligh o g een colou (525 nm, = 0.464). Al e ing he doping si es in O- unc ionalized N-doped s acked complexes can esul in diffe en de-exci a ion cas- cades lowe ing PL QY in CDs including possible occu ence o ISC (Fig. 4g and h). In oxo_s acked2_a, he 350 nm sou ce would cause he popula ing o S 3 localized on PAH, which can in e nally con e o S 1 ia he S 2 s a e, bo h keeping he cha - ac e o LE on PAH. The LE cha ac e is also p ese ed du ing he elaxa ion o he S 1 s a e, despi e no able diffe ences be ween he S 0 and S 1 s uc u es (Fig. S17†). Besides he Kasha emission being in he IR egion (λ max ≈976 nm, = 0.093), a small single – iple ene gy gap ΔE ST = 1.1 kcal mol −1 (Fig. S6†) sugges s he plausibili y o ISC, hus opening a adia- ionless deac i a ion channel. In he case o oxo_s acked2_b, he 350 nm exci a ion sou ce would popula e HLCT S 5 ,CTS 4 and HLCT S 3 s a es. The an- si ion om S 5 o S 1 in ol es hole ans e om IPCA o PAH and back, ollowed by ET om S 3 o S 2 and ib a ion elaxa ion o S 1 .Asinoxo_s acked2_a, he Kasha emission occu s om S 1 localized on PAH uni (see EDD plo in Fig. 4g) a 952 nm ( = 0.091), and he small single – iple ene gy gap ΔE ST = 0.4 kcal mol −1 (Fig. S6†) again sugges s ISC as a possible adia- ionless decay channel. The linking o IPCA wi h N-doped PAHs ia a single co alen bond leads ei he o local emission om IPCA, 23,24 o o a non- adia i e de-exci a ion pa hway lowe ing he PL QY o Fig. 4 De-exci a ion cascade o he non-co alen ly bonded complexes (see Fig. 1 o sys em labeling) exci ed by he 350 nm ene gy sou ce. LE ep esen s local exci a ion, CT (e − /h + ) cha ge (elec on/hole) ans e , HLCT hyb idized local and cha ge- ans e , ET ene gy ans e . Inse s: EDD plo s o he S 0 →S 1 ansi ion ( ed/blue egions indica e inc ease/dec ease o he elec on densi y upon he exci a ion). No e: Fo s acked_edge s uc u e, he S 1* s a e was calcula ed wi h he LR app oach (see ESI† o he explana ion). Pape Nanoscale 4028 |Nanoscale,2023,15,4022–4032 This jou nal is © The Royal Socie y o Chemis y 2023 Open Access A icle. Published on 31 Janua y 2023. Downloaded on 11/20/2023 12:31:33 PM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online CDs, as he Kasha emission occu ing on PAH is ed-shi ed o he ed end o he isible ange wi h low oscilla o s eng h o e en o he IR egion. The in ol emen o low-lying da k CT s a es wi h a hole on PAH and an elec on on IPCA in de-exci- a ion p ocesses in models wi h he es e bond is depic ed in Fig. 5a and b. The S 0 →S 1 ansi ion in es e 1_co e co es- ponding o a LE on PAH is da k and lies in he ed spec al egion (λ max ≈748 nm, = 0.000), while he emission is a in he IR egion (1370 nm, = 0.001), sugges ing a non- adia i e decay. On he o he hand, he S 1 s a e in es e 1_edge model wi h a g aphi ic-N-edge uni is he b igh LE on py ene peaking a 493 nm ( = 0.045), and he emission is shi ed o he ed spec al egion (751 nm, = 0.080) and i only sligh ly dec eases he QY in compa ison wi h he PL o isola ed IPCA molecule. Howe e , i should be no ed ha he S 5 s a e in es e 1_co e is ela i ely well sepa a ed om S 4 , which sugges s ha a compe i i e pa hway ia di ec emission om he S 5 s a e localized on IPCA is plausible. Con a y o o he s udied cases, he 350 nm ene gy sou ce canno ac i a e PL channels o single-bonded complexes o IPCA/N-doped PAHs wi h g aphi ic-N-co e doping pa e n as he e a e no abso p ion peaks in his egion. A lowe ene ge ic sou ce could s imula e a LE on PAH (Fig. 5c) o amide1_co e. I s de-exci a ion om his S 3 s a e only includes he in e nal con e sion o S 1 and he calcula ed e ical emission ene gy in he IR egion (λ= 1372 nm) sugges s non- adia i e deac i a ion (Fig. 5c). I he HLCT s a es amide2_co e and amide3_co e was a ge ed wi h he lowe -ene gy exci a ion sou ce, simila de- exci a ion pa hways could be ollowed in bo h hese models, s a ing wi h elec on ans e om IPCA o PAH (S 4 →S 3 ) and sequen ial in e nal con e sions and ib a ion elaxa ions o S 1 , whe e he exci on is localized on PAH (Fig. 5e and g). The exis - ence o hese complexes would, again, lowe he QY o CDs emission as he emission was calcula ed o be in he IR egion. The amide-bonded complexes wi h g aphi ic-N-edge doping could be pho oexci ed wi h 350 nm lase . In amide1_edge,i would cause LE on PAH (S 0 →S 4 ) and he de-exci a ion would in ol e da k HLCT om PAH o IPCA (S 4 →S 3 ) and back ans- e (S 3 →S 2 ), ollowed by ib a ion elaxa ion o S 1 (Fig. 5d). E en ually, his adia i e channel would lead o emission a Fig. 5 De-exci a ion cascade o he co alen ly bonded complexes exci ed by he 350 nm ene gy sou ce. LE ep esen s local exci a ion, CT (e − /h + ) cha ge (elec on/hole) ans e , HLCT hyb idized local and cha ge- ans e , ET ene gy ans e . Inse s: EDD plo s o he S 0 →S 1 ansi ion ( ed/blue egions indica e inc ease/dec ease o he elec on densi y upon he exci a ion). Nanoscale Pape This jou nal is © The Royal Socie y o Chemis y 2023 Nanoscale,2023,15,4022–4032 | 4029 Open Access A icle. Published on 31 Janua y 2023. Downloaded on 11/20/2023 12:31:33 PM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online 757 nm ( = 0.081). Pho oexci a ion wi h 350 nm ene gy sou ce would also c ea e an exci on pai on PAH in amide2_edge and amide3_edge complexes. Simila de-exci a ion pa hways we e iden i ied o hese wo models, whe e ansi ions be ween b igh HLCT and CT s a es could be acked (Fig. 5 and h; Tables S25 and S27†). The amide2_edge model exhibi ed e i- cal emission a he end o he isible egion, while HLCT cha - ac e o S 1 in amide3_edge esul ed in a non- adia i e de-exci- a ion pa hway, which could be ela ed o smalle dis o ion o he wo componen s in he S1 s a e (Fig. S18†). Mo eo e , ISC canno be excluded om conside a ions as he closes single – iple gap ou o all single-bonded models is 1.9 kcal mol −1 o amide3_edge (Fig. S6†). The o ma ion o used s uc u es in CDs can open ei he adia i e o adia ionless channels depending on he numbe and opology o he g aphi ic ni ogens in hei s uc u e (Fig. 5i–k). In he used model wi h wo g aphi ic ni ogens being emnan s o usion wi h IPCA, he calcula ed Kasha emission was p edic ed a 441 nm ( = 0.834), which is e y close o he IPCA emission band. I he HLCT s a e (354 nm) o used_co e was a ge ed wi h a 350 nm exci a ion sou ce, wo ET could be wi nessed du ing deac i a ion p ocesses o S 1 ,i.e., in e nal con e sion om S 5 o S 4 , and a successi e ET (S 4 →S 2 ) in ol ing wo-s ep hole and elec on ans e s (Fig. 5j). The S 0 →S 1 ansi ion is no b igh (λ max ≈651 nm, = 0.003), and he co esponding Kasha emission is a in IR egion a 1071 nm wi h he low oscilla o s eng h ( = 0.005), sugges ing non- adia i e deac i a ions. Ta ge ing S 4 o used_edge wi h he 350 nm sou ce, elec on CT om IPCA o PAH, back o IPCA and again o PAH a e needed o each he S 1 le el. The S 1 →S 0 emission is in he nea IR egion (λ max ≈945 nm, = 0.023). Al hough he single – iple gap o he S 1 s a e o hese used s uc u es is in he ange o 4.3–15.8 kcal mol −1 , hus discou aging he easibili y o he ISC pa hway, i should be no ed ha he gap de e mined using he GS geome ies can diffe om ha ob ained om he adiaba ic pic u e. The gene al ea u es in ou models ep esen ing in e play be ween co e/su ace and molecula s a es in possible s uc u al domains occu ing wi hin CDs a e summa ized in Fig. 6. Conclusions We analysed abso p ion and emission p ope ies o compu a- ionally easible CD co e/su ace/molecula luo opho e sys ems, ocusing on he possible in e play be ween diffe en PL cen es ia cha ge and ene gy ans e s ha can occu du ing he de-exci a ion p ocesses. By including bo h non-co- alen ly and co alen ly bonded sys ems as well as used s uc- u es, ou models co e ed he main s uc u al domain ypes and hus e lec ed he semi-local complexi y o CDs. Ou esul s e ealed ha all he s udied a angemen s suppo ed, o some ex en , he mu ual communica ion be ween he co e, su ace, and molecula s a es. Howe e , we showed ha , in some cases (e.g., in s acking s uc u es and co alen single- bonded sys ems), he di ec emission om he pho oac i a ed MF compe ed wi h an in e nal con e sion de-exci a ion pa hway, while in o he s (e.g., H-bonded, and used sys ems), Fig. 6 O e iew o he p ocesses occu ing in he ep esen a i e models o CD s uc u al domains a e he i adia ion wi h a 350 nm ene gy sou ce p esumably a ge ing he abso p ion maximum o IPCA (displayed as incoming a ows). The ou coming a ows ep esen he PL (solid lines) om co e and/o molecula s a es and dissipa i e NR channels (dashed lines). No a ion: LE –local exci a ion, CT –cha ge ans e , ET –ene gy ans e , ISC –in e sys em c ossing, NR –non- adia i e de-exci a ion, HB –hyd ogen bond, MF –molecula fluo opho e, PAH –polya oma ic hyd oca bon. Pape Nanoscale 4030 |Nanoscale,2023,15,4022–4032 This jou nal is © The Royal Socie y o Chemis y 2023 Open Access A icle. Published on 31 Janua y 2023. Downloaded on 11/20/2023 12:31:33 PM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online