The more fine structure in absorption spectra of trans-2-StWQ is shown in ethanol than n-hexane indicating that the composition of the rotamer equilibrium mixture varied with solvents. On changing the solvent from nhexane to ethanol, the fluorescence maximum is shifted to short wavelength in contrst to other aza-derivative. However, the fluorescence spectra of trans-2-StQ are insensitive to excitation wavelength in both aprotic solvents and protic solvents. The decay of fluorescence of trans-2-StQ in ethanol at room temperature is found to be monoexponential. These results imply that trans-2-StQ exists in one conformer in various solvents. The calculated energy difference between the two conformers is estimated to 1. 37Kcal/mol. AM 1 calculation also supports that the more planar conformer exists only in n-hexane. The azulene quenching experimental on the direct and sensitized photoisomerization of trans-2-StQ indicate that the direct photoisomerization occurs through both single and triplet excited state in n-hexane, while singlet mechanism for photoisomerization is operative in ethanol.