Mechanistic study of the photochemical hydroxide ion release from 9-hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine.

The excited-state behavior of 9-hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine and its derivative, 9-methoxy-10-methyl-9-phenyl-9,10-dihydroacridine (AcrOR, R = H, Me), was studied via femtosecond and nanosecond UV-vis transient absorption spectroscopy. The solvent effects on C-O bond cleavage were clearly identified: a fast heterolytic cleavage (τ = 108 ps) was observed in protic solvents, while intersystem crossing was observed in aprotic solvents. Fast heterolysis generates 10-methyl-9-phenylacridinium (Acr(+)) and (-)OH, which have a long recombination lifetime (no signal decay was observed within 100 μs). AcrOH exhibits the characteristic behavior needed for its utilization as a chromophore in the pOH jump experiment.