A solvatochromic dye for probing significantly the dipolarity/polarizability of HBD (hydrogen bond donating) environments

The solvatochromism of the novel dye 4-tert-butyl-2-(dicyanomethylene) -5-[4-(diethylamino) benzylidene] D Delta(3)-thiazoline (1) has been investigated in 26 solvents of different polarity. 1 exhibits a positive solvatochromism, its solvent-induced bathochromic UV/Vis absorption band shift ranges from n-hexane (lambda(max) = 566 nm) to dimethyl sulfoxide (lambda(max) = 640 nm). The molar absorption energy of the solvatochromic band shift of 1 can be well correlated with Kamlet-Taft's and Catalan's solvent polarity scales. 1 is mainly sensitive to the solvent's dipolarity/polarizability (pi* of SPPN term) rather than of its HBD (hydrogen-bond donating) or HBA (hydrogen-bond accepting) property. It is emphasized that the UV/Vis absorption band maximum of 1 in the strong HBD solvents acetic acid, 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol fit well in the LSE (linear solvation energy) relationship with Kamlet and Taft's pi* and Catalan's SPPN scale, respectively, which makes this dye important as a dipolarity/polarizability indicator for various solid acids.