Concentration-dependent emission from low molecular weight benzoyl pyrazinium salts

Low molecular weight benzoyl pyrazinium (BP) salts with different structures have been synthesized and analyzed for their photophysical properties. All BP salts studied were found to be optically active in the visible region with structural variations influencing their emission energies. Further, a strong concentration dependence was observed for each BP, whereby dilute solutions had higher emission energies, greater emission intensities and increased recombination lifetimes. NMR data shows that rates of molecular diffusion are slower at higher concentrations suggesting the formation of solution-phase aggregates is responsible for concentration-dependent photophysical behavior, with internal quenching affecting the observed emission at high concentrations. Reliable correlations between energies of excitation and emission were also demonstrated, suggesting that photophysical properties depend on a combination of chemical structure, concentration, and energy of photoexcitation. The BP salts discussed here represent a promising class of easily synthesized low molecular weight organic molecules with tunable emission properties. Benzoyl pyrazinium salts are optically active in the visible region. Photophysical properties depend on chemical structure, concentration, and energy of photoexcitation. They represent a promising class of molecules with tunable emission properties.