Solvatochromism of a typical merocyanine : stilbazolium betaine and its 2,6-di-tert-butyl derivative

The absorption and emission spectra of DTBSB (the 2,6-di-tert-butyl derivative of stilbazolium betaine (SB)), in its neutral and protonated forms, have been measured in 28 solvents. Those corresponding to the parent SB (4'-hydroxy-1-methylstilbazolium betaine or 4-[2-(1-methyl- 1,4-dihydropyridinylidene)ethylidene]cyclohexa-2,5-dien-1-one)) have been recorded in the solvents necessary for comparison. The effect of the ortho bulky groups is to efface the effect of the solvent acidity. The remaining polarity effect on the solvatochromism is very weak but is nevertheless always negative, even in apolar solvents