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Keywords:

Science & Technology, Physical Sciences, Chemistry, Physical, Chemistry, 0306 Physical Chemistry (incl. Structural), 0307 Theoretical and Computational Chemistry, Chemical Physics, 3402 Inorganic chemistry, 3406 Physical chemistry

Abstract:

Upon direct irradiation in dilute dichloromethane solution of polymethylenebis- 2-anthroates two cyclomers are formed: syn head-to-head and syn head-totail. The ratio of these two cycloaddition products is a function of the length of the link between the two anthracene chromopho es : the percentage head-to-tail cyclomer increases with increasing chain length. A bathochromic emission attributed to an excimer is observed for the bis-2-anthroates with a short chain. Fluorescence and cyclomerization quenching experiments suggest the intermediacy of a singlet excited state leading to the head-to-head cyclomer. and an oxci.r uiving the head-t o-tail cyclomer. Kor short chains product formation from this excimer is sterically hindered and fluorescence becomes competitive with the cyclomerization reaction, while for long chains the photocyclomerization is so fast that the excimer is not spectroscopically observable. © by Akademische Verlagsgesellschaft.