Structures, spectra, and lasing properties of new (aminostyryl)pyridinium laser dyes

Recent work from our Photonics Research Laboratory has shown that a new class of hydroxy amino styryl pyridinium derivatives exhibit both one- and two-photon pumped lasing. Because of the exciting prospect of up-conversion lasing by direct two-photon excitation, we have conducted a thorough study of the spectroscopic and lasing properties of a group of related compounds with the objective of understanding the structure-spectroscopic properties relationship. These dyes were found to have two mesomeric forms, one predominant in the ground-state and the other in the excited-state, leading to a large Stokes shift. A low fluorescence quantum yield was observed for all the studied dyes and could be possibly attributed to two factors: (1) the presence of a counterion, iodide, which increases the singlet-to-triplet intersystem crossing transition, and (2) a twisted intramolecular charge-transfer (TICT) geometry derived from the rotation of the amino moiety. However, significant lasing efficiencies were observed under pulse pump conditions possibly because the dyes are being stimulated to emit at a faster rate than the nonradiative processes. From the one-photon pumped laser loss calculations, we found that the losses are only due to the cavity effect. Solvent effect studies for the hydroxy amino styryl pyridinium derivatives showed that the chromophore is very sensitive to hydrogen bonding donor (HBD) solvents. In addition, the dye-doped sol-gel:PMMA composite glass solid matrix exhibits a behavior close to the dye dissolved in water, suggesting a microenvironment of pure silica. These results indicate that the dye is attached to the silica skeleton of the composite glass through hydrogen bonding.