Influence of water on photophysical properties of N-bromobenzyl- or nitrobenzyl derivatives of substituted 4-hydroxystilbazolium hemicyanines

Abstract

Absorption, steady-state and timed-resolved fluorescence spectra of nine N-p-bromobenzyl substituted (E)-4'-hydroxy-4-stilbazolium bromides and N-p-bromo- (or nitro-) benzyl substituted (E)-4'-hydroxy-3'methoxy-4-stilbazolium bromides, belonging to the hemicyanine class of compounds, were studied in dry and water-containing polar solvents and in water. All of the studied compounds displayed negative solvatochromism. In solvents with small amounts of water the solutions of each of the compounds change color to red, blue-green or blue, while in extra dry solvents they are all yellow. The new band causing the change in color is interpreted as belonging to the deprotonated form of the respective compound. The absorption and emission spectra of protonated and deprotonated forms of hemicyanines in solvents are presented in comparison with those of selected, isolated deprotonated forms (merocyanines) of the same compounds. The discrimination between the quinoid and zwitterionic deprotonated forms was achieved based on the absorption band location. Time-resolved fluorescence measurements in selected dry and water-containing solvents were also performed.

Virtual Colorimetric Sensor Array: Single Ionic Liquid for Solvent Discrimination

“…From the foregoing discussions, we conclude that [P 66614 ] 2 [BTB] exhibits a polarity-dependent protonation and deprotonation in the presence of alcohols. In fact, solvent polarity-dependent protonation and deprotonation behavior has been previously described in the literature. − …”

Influence of pH on photophysical properties of (E)-1-(4-chlorobenzyl)-4-(4-hydroxystyryl)pyridinium chloride

“…Indeed, two forms of EPC can exist in 2-propanol, although in different conditions. 1,19 In our previous experiments we identified the quinoid form of deprotonated EPC in insufficiently dry 2-propanol, and the zwitterionic form of EPC in the same 2-propanol, with some NaOH added. We believe that in the presence of NaOH in solutions the zwitterionic form of deprotonated hemicyanines may be stabilized by Na + , forming the -O − Na + ion-pair system.…”