Premium
Triplet BODIPY and AzaBODIPY Derived Donor‐acceptor Dyads: Competitive Electron Transfer versus Intersystem Crossing upon Photoexcitation
Author(s) -
Shao Shuai,
Gobeze Habtom B.,
Bandi Venugopal,
Funk Christiane,
Heine Brian,
Duffy Maddie J.,
Nesterov Vladimir,
Karr Paul A.,
D'Souza Francis
Publication year - 2020
Publication title -
chemphotochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.13
H-Index - 18
ISSN - 2367-0932
DOI - 10.1002/cptc.201900189
Subject(s) - intersystem crossing , bodipy , chemistry , photochemistry , acceptor , electron transfer , homo/lumo , excited state , photoexcitation , photoinduced electron transfer , singlet state , electron acceptor , fluorescence , molecule , atomic physics , organic chemistry , physics , quantum mechanics , condensed matter physics
The bis‐iodo β‐pyrrole‐substituted BF 2 ‐chelated dipyrromethene, I 2 BODIPY, and its structural analogue BF 2 ‐chelated aza dipyrromethene, I 2 azaBODIPY, carrying a nitrogen at the meso ‐position instead of carbon, were synthesized and characterized as new set of triplet sensitizers using different techniques. These sensitizers were further functionalized with fullerene, C 60 , at the central boron atom to build donor‐acceptor conjugates. Using spectral, electrochemical, and computational methods, these conjugates were characterized, and the energy levels were established. Intersystem crossing to populate the triplet state was observed upon excitation of I 2 BODIPY and I 2 azaBODIPY, however, the measured rates of k ISC were found to be nearly two orders of magnitude higher for I 2 azaBODIPY ( k ISC ∼10 11 s −1 ) compared to I 2 BODIPY ( k ISC ∼10 9 s −1 ). The energetics, k ISC , and position of HOMO and LUMO levels was found to control the ability of the dyad to undergo electron transfer, although the donor‐acceptor distances were virtually the same in both I 2 BODIPY‐C 60 and I 2 azaBODIPY‐C 60 conjugates. Free‐energy calculations revealed that the photoinduced electron transfer process was thermodynamically feasible from only the singlet excited states in both conjugates. Consequently, electron transfer from the 1 I 2 BODIPY* in competition with intersystem crossing was witnessed in the case of I 2 BODIPY‐C 60 dyad while in the case of I 2 azaBODIPY‐C 60 dyad, excitation of azaBODIPY led to a short‐lived charge transfer state involving the catechol bridge followed by populating the low‐lying 3 I 2 azaBODIPY* state without promoting the process of charge separation involving C 60 . The lifetime of the charge‐separated states was in the ns range in the I 2 BODIPY‐C 60 conjugate both in polar and nonpolar solvents.