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Ultrafast Photoinduced Charge Separation Leading to High‐Energy Radical Ion‐Pairs in Directly Linked Corrole–C 60 and Triphenylamine–Corrole‐C 60 Donor–Acceptor Conjugates
Author(s) -
Sudhakar Kolanu,
Gokulnath Sabapathi,
Giribabu Lingamallu,
Lim Gary N.,
Trâm Tạ,
D'Souza Francis
Publication year - 2015
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201500679
Subject(s) - corrole , photochemistry , chemistry , ultrafast laser spectroscopy , acceptor , triphenylamine , photoinduced electron transfer , electron transfer , flash photolysis , quenching (fluorescence) , electron acceptor , fullerene , radical ion , ion , fluorescence , reaction rate constant , spectroscopy , organic chemistry , physics , quantum mechanics , kinetics , condensed matter physics
Closely positioned donor–acceptor pairs facilitate electron‐ and energy‐transfer events, relevant to light energy conversion. Here, a triad system TPACor‐C 60 , possessing a free‐base corrole as central unit that linked the energy donor triphenylamine ( TPA ) at the meso position and an electron acceptor fullerene (C 60 ) at the β‐pyrrole position was newly synthesized, as were the component dyads TPA‐Cor and Cor‐C 60 . Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady‐state fluorescence studies showed efficient energy transfer from 1 TPA* to the corrole and subsequent electron transfer from 1 corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron‐transfer products, the corrole radical cation ( Cor ⋅+ in Cor‐C 60 and TPA‐Cor ⋅+ in TPACor‐C 60 ) and fullerene radical anion (C 60 ⋅− ), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, k CS , was found to be about 10 11 s −1 , suggesting the occurrence of an ultrafast charge‐separation process. Interestingly, although an order of magnitude slower than k CS , the rate of charge recombination, k CR , was also found to be rapid ( k CR ≈10 10 s −1 ), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge‐separated species relaxed directly to the ground state in polar solvents while in toluene, formation of 3 corrole* was observed, thus implying that the energy of the charge‐separated state in a nonpolar solvent is higher than the energy of 3 corrole* being about 1.52 eV. That is, ultrafast formation of a high‐energy charge‐separated state in toluene has been achieved in these closely spaced corrole–fullerene donor–acceptor conjugates.