The photokinetic behavior of a photochromic compound, 2,2-spiro-adamantylidene-2H-naphtho[1,2-b]pyran (Py), has been investigated by using monochromatic irradiation in the UV and visible ranges. An unusually complex photochemistry occurs whereby two colored forms (o-quinone–allides) are produced, one of which is thermoreversible whereas the other is not thermoreversible but photoreversible. These are the result of ring opening of the pyran C–O bond to a short lived open-form intermediate which converts to the two different colored forms by twisting around different C–C bonds. Their spectra and molar absorption coefficients were obtained in acetonitrile solution. The kinetic parameters of the thermal bleaching (rate constant and activation energy) and photobleaching (quantum yield) were measured. A plausible reaction mechanism is proposed. Based on this mechanism, mathematical methods were devised which were capable of analyzing the system during its dynamic evolution and evaluating the quantum yields of the color-forming photoreactions.
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Vol. 72 • No. 5