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Investigation of the Solvent-Dependent Photoluminescence Lineshapes in 2,2'-Bithienyl-Substituted 4H-1,2,6- Thiadiazin-4-one

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 π-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.