Photoinduced electron transfer from zinc tetraphenylporphyrin to 2-nitrofluorene in polar solvent acetonitrile

•Zinc tetraphenylporphyrin-2-nitroflurne system is studied for electron transfer.•Observations indicate significant intermolecular photoinduced electron transfer.•Observed fluorescence quenching rates are in good agreement with Marcus theory.•Femtosecond transient absorption data show formation of charge separated state.

The possibility of intermolecular photoinduced ET (PET) is investigated in a novel donor–acceptor (D–A) system consisting of zinc tetraphenylporphyrin (ZnTPP) as donor and 2-nitrofluorene (2NF) as acceptor upon photoexcitation of the former moieties in polar solvent acetonitrile (ACN). The observed values (7.23 × 109 L/(mol s) and 7.04 × 109 L/(mol s)) of the fluorescence quenching rate constant from steady state and time-resolved data, respectively, are in good agreement with that (5.65 × 109 L/(mol s)) obtained from Marcus theory. Excited state absorption (ESA) from the S2 state of Soret excited ZnTPP to higher electronic states gives rise to broad transient absorption spectra in 560–700 nm region. Presence of 2NF leads to a faster decay (up to 100 ps time delay) of the ESA signal of ZnTPP at a probe wavelength of 620 nm. This indicates ultrafast ET from the S2 state (zero vibrational level) as well as the higher vibrational levels of the S1 state of ZnTPP to 2NF. Moreover, transient absorption kinetics at longer time delays (up to 7 ns) at a probe wavelength of 620 nm show the formation of a charge separated state due to ET from the S1 state (zero vibrational level) of the Soret excited ZnTPP to 2NF.

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