Comparison of trifluoroacetyl monostyryl and distyryl dyes: effects of chromophore elongation on the spectral properties and chemical reactivity.

The trifluoroacetyl distyryl derivative 1-[4-(2-[4-[2-(4-dibutylaminophenyl)-vinyl]-phenyl]-vinyl)-phenyl]-2,2,2-trifluoroethanone was compared with the related monostyryl derivative 1-[4-[2-(4-dibutylaminophenyl)-vinyl]-phenyl]-2,2,2-trifluoroethanone with respect to spectral properties and sensitivity to amines. Both trifluoroacetyl derivatives had their absorbance maximum at around 445 nm. The fluorescence of the distyryl dye, however, was observed at significantly longer wavelengths than that of the monostyryl dye, indicating the effect of structural extension of the chromophore system. Furthermore, the distyryl dye exhibited significantly smaller quantum yields in polar solvents than the monostyryl dye. Both dyes were capable of chemically reacting with amines in that their trifluoroacetyl function was converted into a hemiaminal. Consequently, absorbance and fluorescence of both dyes were shifted to shorter wavelengths. The positions of the fluorescence maxima of the spectra when converting from trifluoroacetyl to hemiaminal form were shifted by an almost identical amount for both mono- and distyryl derivative. The hemiaminal form of the distyryl derivative, however, exhibited much larger quantum yields in both polar and nonpolar solvents than the hemiaminal form of the monostyryl dye. The structural extension of the chromophore affected the sensitivity to amines by enhancing the chemical reactivity of the distyryl dye over the monostyryl derivative.