<title>Spectral and holographic characterization of new photochromic compounds based on substituted spiropyrans</title>

Abstract

We report a new photochromic composite polymer consisting of poly-N-epoxypropylcarbazole (PEPC) polymeric matrix with a nitro-brome-substituted spiropyran (BNSP) photochromic dye. The PEPC + BNSP films can be considered as negative photochromic recording media. They are colored in the initial state and bleached upon irradiation within the visible spectra. When we placed the bleached samples to the darkness, they slowly revert to the colored form. This process has strong temperature dependence, so one can either 'freeze'' or accelerate changing of the current coloration state in the PEPC + BNSP. The experimental measurements are evaluated in conjunction with its potential applications for optical holographic recording in the visible spectral range. The real-time holographic recording procedure in PEPC + BNSP films was studied. The diffraction efficiency values reached the maximum of 23 percent at spatial frequency of 1600 line pairs per mm, during direct hologram recording with the 532 nm Coherent VERDI laser irradiation. Light exposures were ranged from 70 to 280 mJ/cm<SUP>2</SUP>. The investigated compounds have good perspectives for use in holography, two-photon optical data storage, electro-optics, and optical-limiting applications due to coupling of some unique properties such as high optical non-linearity, well charge transport, short response times, no-limiting resolution ability, etc.