Multiple fluorescences anomaly of 9,9′-bianthryl in solutions

UV-VIS fluorescence and excitation spectra of 9,9'-bianthryl (BA) in methylcyclohexane (MCH), n-butylchloride (NBC) and acetonitrile (CH3CN) were measured at room and liquid nitrogen temperatures. Three fluorescence bands have been observed depending on the solvent polarity and temperature. In addition, approximate excited state dipole moments have been calculated, and found such as: mu(e), = 0 D (debye) tin NBC at 77 K), 11 less than or equal to mu(e) less than or equal to 14.43 D (in all solvents at room temperature and in CH3CN at 77 K), and mu(e) approximate to 19.70 D tin CH3CN at room temperature). On the basis of these results, a 'multiple states' model has been suggested. So, the fluorescences observed can originate either from: (i) a locally excited state (LE) with no charge transfer and with a twist angle of 90 degrees, around the C-9-C-9 bond; (ii) a partial intramolecular charge transfer (PICT) state with an intermediate twist angle; (iii) a twisted internal charge transfer state (TICT) with a full charge transfer and with a twist angle of 90 degrees. (C) 1999 Elsevier Science B.V. All rights reserved.