Abstract
Energy levels of oligothiophenes (nT: dimer (2T), trimer (3T), tetramer (4T), and pentamer (5T)) in the higher triplet excited state (Tn, n ≥ 2) were estimated from triplet energy transfer (TET) from nT in the Tn state (nT(Tn)) to energy quencher by using the nanosecond−nanosecond two-color two-laser flash photolysis, in which nT in the lowest triplet excited state (nT(T1)) generated with the first laser flash was excited to nT(Tn) during the second laser irradiation. The energy levels (E(Tn)) of 3T(Tn), 4T(Tn), and 5T(Tn) in solution were experimentally estimated to be 3.4 ± 0.1, 3.3 ± 0.1, and 3.2 ± 0.1 eV, respectively, and the estimated energies are assigned to those of the second triplet excited state (T2). The E(T2) was gradually decreased with increasing the number of thiophene rings, suggesting that the triplet exited state in nT is relatively localized even in the higher excited state as well as nT(T1). The TET from the Tm (m ≥ 3) state was also observed.
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