Stationary fluorescence spectra of four acetophenone derivatives were measured in a number of solvents at several temperatures. For 4′-(1-pyrenyl) acetophenone (PYRA) nanosecond fluorescence decay curves and picosecond time-resolved spectra were recorded. Quantum chemical (INDO/S) calculations of the energies, electronic transitions, oscillator strengths and dipole moments were performed for four different conformers of PYRA. Two models are discussed: (i) TICT state formation; (ii) inversion of two low-lying singlet states.
