Time resolved excitation dynamics in emeraldine base

•fs-transient absorption spectra of emeraldine base of polyaniline pumped at 700 nm.•Kinetic master equations for experimental data.•Formation of charge transfer states within 50 fs. Non-radiative decay (0.5 ps).•Phenyl rings relaxation (2.1 ps).•Formation of long-lived polarons (∼ns).

Using femtosecond pump-probe transient absorption spectroscopy (wavelengths 330-800 nm), we observed and explained excited state, charge transfer and polaron state dynamics in emeraldine base form of polyaniline in dimethyl sulfoxide solution. The excited state created by a pump pulse (700 nm) in the quinoid absorption Q-band loses its initial symmetry by subsequent energy transition to a charge transfer state within 50 fs. The hot charge transfer state either recombines non-radiatively into the ground state with decay time constant 0.55 ps or transfers into a relaxed state corresponding to the relaxed phenyl geometry during ca 2.1 ps. This relaxed state shows a prolonged lifetime of about 6.5 ps before its recombination to the ground state. However, a small amount of long-lived polarons with lifetime of about 2 ns in air and with lifetime longer than 6 ns in the solution bubbled with dry N2 was detected.

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