  The solvent dependence of
3,5-bis[(2,2'-bithien)-5-yl]-4H-1,2,6-thiadiazin-4-one BBT is investigated via
absorption and photoluminescence spectroscopies. Large differences are observed
in the photoluminescence (PL) spectra between polar and non-polar solvents.
Narrow bandwidths characterize the PL bandshape in non-polar solvents in
contrast to polar solvents, while in CCl4, a significant contribution is
observed from a blue-shifted species, possibly formed owing to a reaction
between the solvent and the molecule that breaks the {\pi}-conjugation.
Variation of the 0-0 band intensity in the PL spectrum as a function of solvent
suggests that longer H-aggregates have a larger contribution in the case of
polar solvents. Franck-Condon analysis suggests that the solvent dependence of
PL bandshape is owed to the presence of two emissive species in polar solvents.
We propose that the second emissive species observed in polar solvents could be
due to a stabilized charge-transfer state.
