Optical detection of the lowest triplet excited state of oligothiophenes and anthryloligothiophenes

The lowest excited triplet of all-trans oligothiophenes Tn (n = 2 5), 9-anthryl-oligothiophenes A-Tn (n = 1…3) and 9-anthryl-bithienylpyridine A-T2-Py in the crystalline phase has been investigated by delayed fluorescence detected high resolution photoexcitation spectroscopy. For the Tn molecules a 1/n dependence of the triplet energies is observed. On the other hand, the triplet states of the anthracene substituted compounds A-Tn and A-T2-Py do not differ much in energy. Their spectra reflect predominant anthracene character, independent of the chain length.