INVESTIGATION OF PROTONATION EQUILIBRIA AND SPECTROSCOPIC PROPERTIES OF THE (AMINOSTYRYL)PYRIDINIUM CHROMOPHORE IN SOLUTION, SPREAD MONOLAYERS, AND LANGMUIR-BLODGETT-FILMS

The protonation equilibria of the (aminostyryl)pyridinium chromophore have been investigated in aqueous solutions, in spread monolayers at the air/water interface, and in transferred monolayers on solid substrates (LB films) by measuring absorption, emission, and reflection spectra. The results indicate a pH shift for the chromophore in monolayers as compared to the aqueous solution. Further, deprotonation of the dye takes place possibly during transfer to solid substrates, especially when the hydrophilic head groups of the dye are oriented away from the hydrophilic surface of the substrate and a protective layer is coated on top. The equilibrium between the neutral and protonated species of the dye is reversibly shifted in LB films by reaction with gas-phase HCl or NH3 with no discernible degradation in optical quality. © 1990 American Chemical Society.