| Abstract
| - The phosphorescence spectra of a series of small oligothiophenes (nT, n = 1−3) incorporating a variety ofsubstituents, end cappers, and functional groups have been recorded for the first time using gated detectionin combination with nanosecond excitation in frozen solution at 80 K. The vibrationally resolved emissionspectra provide accurate estimates of the T1 and S1 levels, and the singlet−triplet energy gap. Theoreticalquantum chemical calculations performed at the DFT (B3LYP/6-31G*) level reproduce all experimental trendsaccurately and provide quantitative description of the S0−T1 energy difference. The geometry relaxation inthe excited state shows that the “natural” size of the triplet exciton is about 3−4 thiophene units.
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