EFFECTS OF WATER ON THE PHOSPHORESCENCE SPECTRA OF AROMATIC CARBONYL-COMPOUNDS .3. DUAL-COMPONENT OR MULTIPLE-COMPONENT PHOSPHORESCENCE OF 1-INDANONE AT 77 K IN SOME PROTIC SOLVENTS CONTAINING WATER

Phosphorescence spectra of 1-indanone (IND) at 77 K in protic solvents such as EPA (diethyl ester-isopentane-ethanol, 5:5:2 volume ratio) ME (methanol-ethanol, 1:1 volume ratio) and ethanol (each containing wat er) have been found to exhibit dual phosphorescence with short (2.5-2. 7 ms) and long (18.4-30.0 ms) lifetimes. Since the phosphorescence spe ctrum with the short lifetime is identical to that found in an aprotic Solvent such as methylcyclohexane (without the addition of H2O), the short-lived emitting species is attributed to free triplet IND of n pi character, while the long-lived emitting species is attributed to a complex (triplet IND-H2O with a fixed number of H2O molecules) of mixe d n pi-pi pi* character. The phosphorescence decay curve of IND in a strong hydrogen-bonding solvent such as 2,2,2-trifluoroethanol (TFE) ( containing H2O) can also be reproduced by a biexponential function, bu t the corresponding lifetimes are found to change with the sweeping ti me of the oscilloscope. It is supposed that only the shortest and long est lifetimes are true values, while the other lifetimes are fortuitou s values owing to the existence of various types of emitting species. Changing the H2O content, moreover, it is found that the shortest life time is independent of the H2O content, while the longest lifetime inc reases linearly with increasing H2O content; the maximum lifetime (603 ms) is reached at an H2O content of ca. 7 vol.%. Since no clear emiss ion peaks reflecting the progression of the carbonyl vibration can be seen, the emitting species with the shortest lifetime (2.9 ms) is ascr ibed to triplet IND (hydrogen-bonded with TFE) of mixed n pi-n pi* ch aracter, while the long-lived emitting species are attributed to sever al types of complexes (triplet IND-H2O or triplet IND-H2O-TFE with var ious numbers of H2O molecules) of mixed n pi-pi pi* or pi pi* charact er depending on the number of H2O molecules contained in the complex. No long-lived emission originating from triplet IND hydrogen-bonded wi th the alcohol molecule is observed.