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# THE PHOTOCHROMISM OF CELLULOSE Henrik Tylli (a), Ingegerd Forsskåhl (b) and Carola Olkkonen (a) (a) Department of Chemistry, University of Helsinki, P.O.Box 55, FIN-00014 Helsinki, Finland (b) The Finnish Pulp and Paper Research Institute (KCL), Paper Science Centre, P.O.Box 70, FIN-02151 Espoo, Finland E-mail: henrik.tylli@csc.fi ABSTRACT A clear photochromism, comprising a fairly rapid emission decrease during irradiation at 350 nm and a slower emission recovery in the dark at room temperature was observed for cellulose samples. Similar behaviour was found for cotton cellulose, for cellulose immersed into water and for microcrystalline cellulose. The emission recovery was less efficient for samples immersed into deaerated water. Thus, a chromophore regeneration mechanism not dependent on the availability of oxygen is supported. Samples of microcrystalline cellulose show a considerably faster emission recovery than cotton cellulose. Cellulose treated with ozone shows a more pronounced photochromism than untreated cellulose. Thus, carbonyl and lactone type structures are likely to be involved in the rearrangements.