Kinetics of Hydrogen Bonding between Anthracene Urea Derivatives and Anions in the Excited State

Urea compounds are useful anion sensors due to their hydrogen-bonding capabilities. We investigated the emissive properties of complexes consisting of urea anthracene (nPUA, n = 1, 2) host compounds and acetate anions held as guests through intermolecular hydrogen bonding. The kinetics of a new emission band formed by conformational changes in the excited singlet state were revealed. The new band is thought to arise from a charge-transfer interaction between the anthracene and urea moieties after intermolecular hydrogen-bond reconfiguration in the excited state, with rate constants of 2.4 x 10(9) and 4.0 x 10(7) s(-1) for 1PUA and 2PUA, respectively.