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Photoinduced Electron Transfer in Zinc Naphthalocyanine–Naphthalenediimide Supramolecular Dyads
Author(s) -
ElKhouly Mohamed E.,
Moiseev Andrey G.,
van der Est Art,
Fukuzumi Shunichi
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100948
Subject(s) - chemistry , photochemistry , ultrafast laser spectroscopy , exergonic reaction , singlet state , photoinduced electron transfer , photoinduced charge separation , quenching (fluorescence) , electron transfer , triplet state , supramolecular chemistry , fluorescence , excited state , spectroscopy , photocatalysis , molecule , artificial photosynthesis , organic chemistry , atomic physics , physics , quantum mechanics , catalysis
Photoinduced electron transfer was studied in self‐assembled donor–acceptor dyads, formed by axial coordination of pyridine appended with naphthalenediimide (NDI) to zinc naphthalocyanine (ZnNc). The NDI‐py:ZnNc ( 1 ) and NDI(CH 2 ) 2 ‐py:ZnNc ( 2 ) self‐assembled dyads absorb light over a wide region of the UV/Vis/near infrared (NIR) spectrum. The formation constants of the dyads 1 and 2 in toluene were found to be 2.5×10 4 and 2.2×10 4 M −1 , respectively, from the steady‐state absorption and emission measurements, suggesting moderately stable complex formation. Fluorescence quenching was observed upon the coordination of the pyridine‐appended NDI to ZnNc in toluene. The energy‐level diagram derived from electrochemical and optical data suggests that exergonic charge separation through the singlet state of ZnNc ( 1 ZnNc*) provides the main quenching pathway. Clear evidence for charge separation from the singlet state of ZnNc to NDI was provided by femtosecond laser photolysis measurements of the characteristic absorption bands of the ZnNc radical cation in the NIR region at 960 nm and the NDI radical anion in the visible region. The rates of charge‐separation of 1 and 2 were found to be 2.2×10 10 and 4.4×10 9 s −1 , respectively, indicating fast and efficient charge separation (CS). The rates of charge recombination (CR) and the lifetimes of the charge‐separated states were found to be 8.50×10 8 s −1 (1.2 ns) for 1 and 1.90×10 8 s −1 (5.3 ns) for 2 . These values indicate that the rates of the CS and CR processes decrease as the length of the spacer increases. Their absorption over a wide portion of the solar spectrum and the high ratio of the CS/CR rates suggests that the self‐assembled NDI‐py:ZnNc and NDI(CH 2 ) 2 ‐py:ZnNc dyads are useful as photosynthetic models.