Light-harvesting subphthalocyanine–ferrocenophane
(SubPc–Fc; 1) and subphthalocyanine–naphthalenediimide
(SubPc–NDI; 2) dyads have been synthesized, characterized,
and probed
by femtosecond laser photolysis. In dyads 1 and 2, both the electron-donating ferrocenophane and the electron-accepting
naphthalenediimide are axially linked with the functional O–Ph
groups (at the para position) in the axial positions of SubPc. Electrochemical
data show that the SubPcs can act as both electron donors and electron
acceptors. The geometric and electronic structures of dyads 1 and 2 were calculated by ab initio B3LYP/6-311G
methods. The optimized structures showed that the Fc and NDI entities
are separated from SubPc by 8.32 Å (for dyad 1)
and 8.85 Å (For dyad 2). The distribution of HOMOs
and LUMOs suggests the formation of SubPc•––Fc+ and SubPc•+–NDI•– as charge-separated states for dyads 1 and 2, respectively. Upon photoexcitation of
the subphthalocyanine unit, these arrays undergo photoinduced electron
transfer to form the corresponding charge-separated species, SubPc•––Fc+ and SubPc•+ −NDI•–, in which SubPc acts as an
electron acceptor and an electron donor, respectively, as expected
from their redox potentials determined by cyclic voltammetry. Femtosecond
transient spectroscopic studies have revealed that a fast charge separation
(1011∼1012 s–1) occurs
for dyads 1 and 2. From the kinetic studies,
the rate of charge recombination and the lifetime of the charge-separated
state (SubPc•+–NDI•–) were found to be 2.9 × 109 s–1 and 345 ps, respectively.
Photoinduced processes of a newly synthesized subphthalocyanine–diazobenzene–fullerene triad have been studied by the time-resolved spectroscopic techniques. On photo-excitation of subphthalocyanine (SubPc) moiety, the fluorescence quenching of SubPc was observed, suggesting the energy-transfer process from singlet excited energy of the light-harvesting SubPc to C60 through diazobenzene. This finding is confirmed by the nanosecond transient absorption of the triplet excited state of C60.
Electron-transfer reaction of the newly synthesized light harvesting pentad composed of silicon phthalocyanine (SiPc) that is connected with two fullerene C 60 and two azobenzene units to form SiPc -(azobenzene)2-( C 60)2 pentad has been studied by laser flash photolysis and other complementary techniques. This combination between SiPc , azobenzene and C 60 in the examined SiPc -(azobenzene)2-( C 60)2 pentad leads to strong light absorption over the whole visible spectrum. Photoexcitation of the pentad results in rapid formation of the charge-separated state by photoinduced electron transfer from the singlet-excited state of the SiPc moiety to the C 60 moiety. The charge-separated state has a lifetime of 2.50 ns in benzonitrile.
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