No abstract

The present work reports measurements of S T intersystem crossing quantum yields of acridine in polar and nonpolar solvents, using the third harmonic of a Nd-glass laser. The intersystem crossing yield was determined by comparing the triplet formation of acridine with that of anthracene in ethanol, used as a reference. The quantum yields of acridine in benzene, tert-butyl alcohol, and water were found to be 0.73, 0.61, and 0.39, respectively. These data combined with the fluorescence yields show the existence of internal conversion from the first excited singlet state of acridine in the three solvents. The results indicate a strong solvent effect for the rate constants of the radiationless transitions. No significant deuterium effect was observed on the quantum yields.

Photochemical reactions of acridine orange (AO) in basic aqueous and ethanolic solutions were studied using the flash photolysis technique. The absorption spectrum of A 0 was determined in detail (230-900 nm) and extinction coefficients were obtained. The decay of the triplet state is the result of a first order process, a triplet-triplet annihilation process and a quenching by the dye in the ground state. The main part of the triplet decays to the ground state; however the observation of semi-reduced A 0 shows that the decay is partly due to chemical reactions.An efficient reversible reaction is observed on flashing aqueous solutions of A 0 containing tetramethyl-p-phenylenediamine: semi-reduced A 0 is formed in high yield by reaction between the triplet dye and the diamine. In addition, irreversible reactions of A 0 occur; these are shown to be due to the triplet state by the method of triplet energy transfer.