Kinetics of Decolorization of Spironaphthooxazine-Doped Photochromic Polymer Films Don Keun Lee, † Hyun Gil Cha, ‡ Umapada Pal, ‡,§ and Young Soo Kang* ,‡ Cheil Industries Inc. Pyeongyeo-Dong, Yeosu-si, Jeollanam-do 555-210, Republic of Korea, and Department of Chemistry, Sogang UniVersity, Shinsu-dong, Seoul 121-742, Republic of Korea ReceiVed: June 17, 2009; ReVised Manuscript ReceiVed: August 10, 2009 Photochromic polymeric films were prepared by doping photochromic dye spironaphthooxazine into polymer resin gels such as polyurethane, vinyl copolymer, and copolymer of vinyl and nitorocellulose at different concentrations. All of the composite films show normal photochromism. The kinetics of the photochromism/ decoloration in the films were quantified by fitting biexponential equations to their photochromic decay curves after irradiation. It was observed that the decoration process is faster in vinyl copolymer than that in the copolymer of vinyl and nitrocellulose and is the slowest in the case of polyurethane. The decoloration mechanisms of spironaphthooxazine in those polymeric matrixes have been discussed. Introduction Several materials such as dyes and other chemical systems exhibit a color change when they are exposed to certain types of radiation and regain their original color upon removing the irradiation. This reversible color change process has been called photochromism. Photochromism of organic compounds in heterogeneous systems is a phenomenon of great interest not only for practical applications but also for elucidating primary photochemical reactions. 1-4 The photophysical processes of aromatic carbonyl molecules in solutions and solid matrixes depend on the geometrical and electronic properties of individual molecules, as well as on the physicochemical properties of the surrounding media. 5,6 Photochromism is also accompanied by changes in the refractive index, dielectric constant, enthalpy, and so forth. These modifications other than color change are intrinsic phenomena, which offer vast possibilities of practical applications of these photochromic compounds. As the reversible property variation in photochromic compounds are induced by molecular-level changes, several changes in physical as well as chemical properties may be observed when photoisomerized molecules trigger subsequent rearrangements of microenviron- mental states upon light absorption. Therefore, photochromic materials act essentially as transducers and should be called photoresponsive materials, the properties of which change reversibly. Photochromic systems exhibiting phase transitions with a number of photoresponsive polymers have been studied widely in the areas of micelles, vesicles, and liquid crystals. 7 Such phase transitions are extremely sensitive to changes in the molecular structure of photochromic compounds and have potential significance in practical applications. The decoloration kinetics and color reversibility are the essential properties of photochro- mic materials for various applications. However, irreversible degradation upon prolonged light irradiation of photochromic materials sometimes restricts their practical uses. The decol- oration kinetics of photochromic materials in different matrixes depend on the characteristics of the host, such as the polarity and rigidity, which critically affect the physical and chemical functions of the photochromic materials. In previous studies, the kinetics and rigidity of the glass gel matrixes and polymeric systems were intensively studied by doping photosensitive organic photochromic and photosensitive compounds. 8-12 The kinetics of the photochromic change of the molecules doped in the polymer matrixes were critically dependent on the kind and structure of the polymer matrixes and glass gel matrixes. The rigidity of the matrix around a photosensitive molecule can control its relaxation kinetics after light excitation. Photoinduced radical yields of photosensitive molecules such as viologens, phenothiazines, and benzidines in inorganic silicate matrixes were studied with electron paramagnetic resonance (EPR) and UV-vis diffuse reflectance spectroscopies. 13-16 Charge recom- bination of electron-cation pairs formed in polymer solids through two-photon ionization was examined in terms of long- range electron transfer by electron tuinneling. 17 In those studies, the yield of the photoproduced radicals was controlled by matrix rigidity and the long-range electron-transfer distance. The photoionization of N-methylphenothiazine in poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) matrixes was studied with EPR and electron nuclear double resonance (ENDOR). 18 The decay time of the photogenerated radicals in PEO and PPO at 77 K was studied by determining the amount of the remaining radicals with exposure time. Kinetic constants for biexponential decay of the cation radicals were obtained. The photochromic effect and spatial light modulation in photosensitive-dye-doped polymeric films have also been studied. 19-25 Spironaphthooxazine, a highly photostable and photosensitive organic dye, was doped into different polymeric gel matrixes such as polyurethane, vinyl copolymer, and a copolymer of vinyl and nitrocellulose in the present study. 26 Those polymer films are commercially available and widely applied for plastic coatings. The photochromatic behaviors of the dye doped in polymer matrixes of different polarity and structure are studied. Experimental Section Materials. 1,3-Dihydro-1,3,3-trimethyl-spiro[2H]-indole-2,3′- [3H]-naphtho[2,1,b][1,4]-oxazine (Figure 1A) was obtained from Aldrich Chemical Co. and used without any further purification. The polyurethane, vinyl copolymer, and copolymer of vinyl and * To whom correspondence should be addressed. E-mail: yskang@ sogang.ac.kr. † Cheil Industries Inc. Pyeongyeo-Dong. ‡ Sogang University. § On leave from Universidad Autonoma de Puebla, Mexico. J. Phys. Chem. B 2009, 113, 12923–12927 12923 10.1021/jp905700s CCC: $40.75  2009 American Chemical Society Published on Web 09/08/2009