The absorption and fluorescence study of 1,4,5,8-naphthalenetetracarboxy diimides in their low-energy 11B2u and 11B3u electronic states. The Franck–Condon analysis in terms of CASSCF method

The electronic structure of the low-energy states of 1,4,5,8-naphthalenetetracarboxy diimide (1) is investigated in terms of CASSCF method. At this level of approximation the Franck–Condon (FC) parameters were evaluated for the 13 totally symmetric modes of (1) molecule in its dipole-allowed low-energy 11B2u and 11B3u electronic states. These parameters are then employed to simulate the vibrational structures of absorption and fluorescence spectra of N,N′-dibutyl (2) and N,N′-bis-hydroxypropyl (3) derivatives of naphthyl diimides measured in the region corresponding to the low-energy 11Ag → 11B2u and 11Ag → 11B3u overlapping transitions.