NMR studies of the structure of the photoinduced forms of photochromic spironaphthoxazines
Abstract
Irradiation at 355 nm with a pulsed laser of the colourless
1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3′-[3H
]-naphth[2,1-b][1,4]oxazine] results in formation of
photomerocyanines (coloured forms of photochromic compounds); this and
its chloro derivative were studied by NMR spectroscopy. This has allowed
us to confirm the structure of the stereoisomers. The colourless and
coloured forms exist in thermal equilibrium. Integration of certain
photomerocyanine signals allowed us to calculate the thermal kinetics of
bleaching k, the half-life τ and the
activation enthalpy ωH
‡ at
different low temperatures and from these temperature dependence studies
of the thermal decay rate, the thermal energy barrier for the decay of
the coloured metastable state to the colourless form was
determined.
‡ at
different low temperatures and from these temperature dependence studies
of the thermal decay rate, the thermal energy barrier for the decay of
the coloured metastable state to the colourless form was
determined.
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