Triplet-Triplet Spectroscopy of Polyacenes

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Abstract
Complete triplet—triplet absorption spectra (2000–10000 Å) were measured in alcoholic solution at 113°K with naphthalene, anthracene, tetracene, and a few methylated derivatives. Several new bands were observed. Calculations of the higher ππ* triplet states energies with the LCAO—MO—SCF Pariser—Parr—Pople method were improved by the use of large configuration interactions. These include many doubly excited configurations with respect to both the ground singlet state S0 and the lowest triplet state T1, thanks to the systematic use of all monoexcitations with respect to S0 plus all monoexcitations with respect to T1. The comparison of all experimental and theoretical results for the three polyacenes allows one to modify a few previous assignments and to give a general tentative assignment for all observed transitions.