OBSERVATION OF A REMARKABLE DEPENDENCE OF THE RATE OF SINGLET SINGLET ENERGY-TRANSFER ON THE CONFIGURATION OF THE HYDROCARBON BRIDGE IN BICHROMOPHORIC SYSTEMS

Intramolecular singlet energy transfer can be detected in a series of rigid bichromophoric molecules (1(n)) where a dimethoxynaphthalene chromophore and a carbonyl chromophore are separated by extended all-trans arrays of up to eight C-C σ bonds (1(8)). In the series of compounds 2(n) “kinks” are introduced in the array of σ bonds of the saturated hydrocarbon system, which bridges the chromophores. Singlet energy transfer is then much less efficient (i.e. in 2(6)) or even absent (i.e. in 2(8)), which supports the earlier interpretation of the energy transfer mechanism in 1(b) as being mainly mediated by through-bond exchange interaction and furthermore explains the virtual absence of such interaction in more flexible systems where the chromophores are linked by polymethylene bridges. © 1990, American Chemical Society. All rights reserved.