Modulating chemical reactivity using a photoresponsive molecular switch

The kinetics of an alkylation reaction are used to probe the effect of an electron-withdrawing pyridinium group on the nucleophilicity of a free pyridine in a photoresponsive dithienylcyclopentene (DTCP) derivative in order to demonstrate effective and reversible control over chemical reactivity. The kinetic data support the hypothesis that the ring-open isomer of the DTCP (1o) is more reactive than its ring-closed counterpart (1c) due to electronic communication between the two pyridine groups existing only in the latter isomer. The rates of the alkylation reactions of bis(pyridine) versions of the photochromic compounds are also evaluated to provide a better understanding of the through-bond and the through-space effects of the groups located at the ends of the linearly conjugated pi-electron backbone. The use of the two DTCP isomers (1o and 1c) as nucleophilic catalysts is also suggested in preliminary investigations. (C) 2008 Elsevier Ltd. All rights reserved.