Intramolecular charge transfer dynamics in the excited states of diphenylamine substituted 1,3,4-oxadiazole derivatives

Abstract

The excited state dynamics processes of two diphenylamine substituted symmetric 1,3,4-oxadiazole derivatives in different solvents were studied through femtosecond transient absorption spectroscopy. It was revealed that in cyclohexane, the locally excited (LE) state relaxes to the intramolecular charge transfer (ICT) state within 2 ps timescale, then decays to the ground state. In tetrahydrofuran and acetonitrile, the ICT state can be stabilized via solvation, so besides the LE → ICT conversion within 1 ps, another ICT → solvent stabilized ICT (SSICT) conversion in the 1-200 ps time scale could also be observed, and eventually decay to the ground state. Whereas, ICT → SSICT process in acetonitrile is slower than that in tetrahydrofuran, which leads to radiationless deactivation dominates the ICT state deactivation process and low fluorescence quantum efficiency. These results offer a guidance to understand the relationship of low fluorescence quantum efficiency and excited state deactivation mechanism of organic π-conjugated molecules, which would be very helpful for designing new advanced opto-electronic materials.

Keywords: 1, 3, 4-oxadiazole derivatives; Femtosecond transient absorption spectra; Intramolecular charge transfer.