Effect of Various Anions and Zwitterions on the Lasing Properties of a Photostable Cationic Laser Dye

An unusually photostable cationic laser dye first prepared by quaternization of the free base 4PyMPO (Figure 1) with methyl p-toluenesulfonate unexpectedly had, when flashlamp pumped in methanol, half the energy output of four other N-methyl quaternary salts: the methanesulfonate, the trifluoromethanesulfonate, the perchlorate, and the tetrafluoroborate. When four homologous zwitterions (Figure 2) prepared from4PyMPO were tested in methanol, the output energies ranged from 1.4 to 2.5 times that of the p-toluenesulfonate, and up to 1.3 times that of the salt with the highest output. When flashlamp pumped in water, the zwitterions showed 1.5 to 2.0 times the output energy of the p-toluenesulfonate in water. Many of the dyes displayed laser output curves that were split in the middle, so that lasing energy appeared on either side of a dark valley. Among the zwitterions, a regular shifting from red to blue was observed as the carbon chain length was increased.