Mm. Alam et al., CHARACTERIZATION AND REACTIVITIES OF TRANSIENT SPECIES GENERATED BY LASER FLASH-PHOTOLYSIS OF N-HYDROXYPYRIDINE-4-THIONE, Journal of the Chemical Society. Perkin transactions. II (Print), (11), 1998, pp. 2471-2476
The reaction intermediates produced by the nanosecond-laser-flash phot
olysis of N-hydroxypyridine-4-thione (4-HOPyT) have been studied in aq
ueous and nonaqueous solutions. The pyridlyl-4-thiyl radical (4-PyS. a
t 420 nm) and (OH)-O-. are formed by the homolytic N-OH bond cleavage
of 4-HOPyT. The 720-nm band was assigned to the pyridyl-N-oxyl radical
(4-S=PyO.) generated by the photodissociation of the O-H bond and by
H abstraction from 4-HOPyT through (OH)-O-.. The triplet state of 4-HO
PyT [(3)(4-HOPyT)], confirmed by energy transfer with triplet quenche
rs, is also produced concomitantly with the radical species. Diffusion
controlled electron-transfer reactions occur between (3)(4-HOPyT) an
d donors (or accepters), which may be caused by the relatively high tr
iplet state energy (E-T1 = 60.1 kcal mol(-1)) of (3)(4-HOPyT). In aqu
eous alkaline solution, the solvated electron (e(aq)(-)) and the one-e
lectron semioxidized radical of 4-HOPyT (4-S=PyO.) are produced by pho
toionization of the anionic form of 4-HOPyT. Thus, it is possible to c
ontrol the generation of (OH)-O-. and e(aq)(-) by changing the pH of t
he solution.