Thermal Back‐Isomerization of Spirocyclic Naphtho‐oxazine and Phenanthro‐oxazine Derivatives in Alcohols,Nitriles, and Poly(alkyl methacrylates)

The thermal back‐isomerization of spiroindole‐naphtho‐oxazine] 1 and spiroindole‐phenanthro‐oxazine] 2 was studied in a series of primary alcohols, nitriles, and poly(methylmethacrylate), poly(ethylmethacrylate), and poly(isobutyl methacrylate) films by laser‐flash photolysis in the temperature range of 0 – 70°. The decay is monoexponential in fluid solution, but deviates strongly from this behavior in polymeric environments even above the glass transition temperature of the polymers (Tg). In liquids, a very small solvent effect is observed on the isomerization rate constants (k_iso) for 1 , which is attributed mostly to the solvent viscosity η. The values of k_iso for 2 show influence of solvent viscosity and polarity, which were studied by application of a semiempirical relationship that accounts for non‐Markovian processes. The decay kinetics in polymers was described by a Gaussian distribution of the activation energy and by a kinetic model that takes into account the simultaneous relaxation of the probe and the environment. For 1 and 2 , the rate constant at the center of the Gaussian distribution is very similar to the first‐order rate constant in nonpolar solvents. The Gaussian width of the distribution (σ) decreases with temperature and is very similar in all polymers under Tg, and, above Tg, σ decreases more abruptly. We make comparisons of the parameters derived from analysis of both 1 and 2 in polymers, as well as of their behaviors in solution and in polymers.