ABSORPTION AND FLUORESCENCE PROPERTIES OF TETRACOORDINATED BORATES - ENERGY VERSUS ELECTRON-TRANSFER IN SPIROINTERACTIONS

Bicyclic berates can have two pi-planes oriented perpendicular to each other through four tetrahedral B-O bonds and exhibit spirointeraction s as revealed by the presence of broad charge transfer bands, although absorption peaks of the contributory moieties were hardly modified. T heir fluorescence spectra demonstrate that the spirointeractions allow intramolecular quenching of two moieties by electron transfer but not by energy transfer. The overall phenomenon related to the spiroconjug ation indicates a new pattern of excited-state interaction distinguish able from that of exciplex formation in intermolecular quenching and e lectron transfer through rigid sigma-bond systems. (C) 1997 Published by Elsevier Science B.V.