Journal of zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA M olecular Structure, 219 (1990) 359-364 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands 359 PHOTOISOMERIZATION OF PROVITAMIN D IN DISPERSIVE SYSTEMS I.P. TERENETSKAYAI, O.G. PERMINOVA2 and A.M. YEREMENK02 ‘Institute of Physics 252028, Kiev-28 (USSR) Ukrainian Academy of Sciences, 'Institute of Surface Chemistry, Ukrainian Academy 252028, Kiev-28 (USSR) SUMMARY The kinetics of provitamin D photoisomerization in solutions of Sciences, and silica gel-solvent matrixs upon lamp irradiation on 254 nm was measured by W spectroscopy. The reduction of the efficiency for cis-trans isomerization in dispersive systems was revealed as compared with the solutions and the effect was established to exhibit a very substantial solvent polarity dependence. The well known concept of ground-state conformational control was utilized to explain the influence of the adsorption on the photo- behaviour of provitamin D. More importantly, the results obtained reveal that the dispersive systems can be used in the certain cases to control the conformations of organic molecules and photoproducts distribution. INTRODUCTION The effect of adsorption on spectsoscopic properties of organic molecules has been well studied for polyacenes and it generally has been found that adsorption may cause essential changes of their optical spectra due to participation of %-electrons into interaction with surface. It is of interest to investigate the influence of adsorption on spectra and photobehaviour of such molecules in which chromo- phore and intramolecular group responsible for the interaction with surface are spatially separated. As such we have chosen the molecule of provitamin D in which the diene chromofore is found in the central ring whilst adsorption is believed to result from the interaction with the most polar OH group on the end of molecule. The present paper is concerned with a comparative study of spectra and photoisomerization of provitamin D in solutions of different polarity and dispersive systems (solvent + adsorbent). The well known scheme of reversible interconvertions of zyxwvutsrqponmlkjihgf 0022-2860/90/$03.50 0 1990 Elsevier Science Publishers B.V.