PROTON-TRANSFER PROCESSES IN WELL-DEFINED MEDIA - EXPERIMENTAL INVESTIGATION OF PHOTOINDUCED AND THERMAL PROTON-TRANSFER PROCESSES IN SINGLE-CRYSTALS OF 2-(2,4-DINITROBENZYL)PYRIDINE DERIVATIVES
M. Scherl et al., PROTON-TRANSFER PROCESSES IN WELL-DEFINED MEDIA - EXPERIMENTAL INVESTIGATION OF PHOTOINDUCED AND THERMAL PROTON-TRANSFER PROCESSES IN SINGLE-CRYSTALS OF 2-(2,4-DINITROBENZYL)PYRIDINE DERIVATIVES, Journal of physical chemistry, 100(40), 1996, pp. 16175-16186
A detailed spectroscopic study of photoinduced and thermally activated
proton-transfer processes for a series of different crystals of 2-(2,
4-dinitrobenzyl)pyridine derivatives has been performed. The quantitat
ive analysis of ground- and excited-state activation barriers and pree
xponential factors in deuterated and nondeuterated crystals shows clea
rly that the observed photochromism is linked to a proton-transfer pro
cess. Furthermore, it is clearly seen that the supramolecular environm
ent of the transferred proton participates in the proton-transfer proc
ess. These supramolecular effects control the relative rates and effic
iencies of the observed proton-transfer processes in both the ground a
nd excited state, yielding, at room temperature, photoproducts having
lifetimes ranging between hours and weeks. At least two proton-accepti
ng groups may be active in the abstraction of the proton from its rela
tively stable benzylic position. Additionally, low-temperature measure
ments of proton-transfer processes show that tunneling processes preva
il at temperatures below 100 K only in the excited state. No evidence
for tunneling could be found for ground-state processes.