Ultrafast
Electron Injection, Hole Transfer, and Charge
Recombination Dynamics in CdSe QD Super-Sensitized Re(I)–Polypyridyl
Complexes with Catechol and Resorcinol Moiety: Effect of Coupling
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Abstract
Ultrafast
charge-transfer dynamics have been demonstrated in CdSe
quantum dots (QD) using two Re(I)–polypyridyl complexes having
pendent catechol (<b>Re1,2</b>) and resorcinol (<b>Re1,3</b>) as the sensitizer molecules. The energy level diagram of CdSe QD
and <b>Re1,2</b> and <b>Re1,3</b> sensitizer reveals that
photoexcited hole of CdSe QD can be transferred to both <b>Re1,2</b> and <b>Re1,3</b> molecule, and photoexcited <b>Re1,2</b> and <b>Re1,3</b> can inject electron in the conduction band,
which has been confirmed by steady-state and time-resolved photoluminescence
studies with selective photoexcitation. Femtosecond transient absorption
studies have been carried out to monitor charge-transfer dynamics
in early time scale. Transient absorption spectra show formation of
cation radicals for both <b>Re1,2</b> and <b>Re1,3</b> in the 550–650 nm region with a peak at 590 nm region and
broad absorption in the 650–1000 nm region, which can be attributed
to photoexcited electron in the conduction band of CdSe QD. Charge
recombination was determined by monitoring the decay of cation radicals
as well as decay of an electron and found to be slower in the <b>Re1,3</b>/CdSe system as compared to that of the <b>Re1,2</b>/CdSe system, which is due to weaker electronic coupling in the former
system