Photophysics and spectroscopy of 1,2-Benzazulene

[Display omitted] •First detailed report of photophysical processes in 1,2-benzazulene, an important derivative of azulene.•Interesting differences between the S2 – S0 spectra of azulene and 1,2-benzazulene.•Clear evidence that 1,2-benzazulene follows the energy gap law in its S2 – S1 radiationless relaxation.•Assessment of the possibility of S2 + S0 → 2 T1 singlet fission. The electronic spectroscopy and photophysics of 1,2-benzazulene (BzAz) have been examined in solution and in thin solid films, with the objective of comparing its intramolecular and intermolecular excited state decay processes with those of azulene. Unlike azulene, the S2 – S0 absorption and fluorescence spectra exhibit a clear mirror image relationship dominated by a single strong Franck-Condon active progression. Picosecond transient absorption spectra and non-linear S2 fluorescence upconversion experiments reveal lifetimes that follow a well-established energy gap law correlation, indicative of a dominant S2 – S1 decay route. Mechanistic interpretations, including the possibility of S2 singlet fission in aggregates, are discussed.