Layered molecules with intra-molecular donor–acceptor interactions

Abstract

Layered molecules are donor-acceptor cyclophanes in which the mutual orientation and/or location of the donor and acceptor ring systems can be altered to investigate the conditions for maximum overlap and hence charge transfer. The enhancement of charge transfer in pseudogeminal, as opposed to pseudo-ortho cyclophanes, has been demonstrated by comparison of UV-visible spectra for many diastereoisomeric pairs. Crystal structure determinations show that there is superposition of donor and acceptor moieties in the paracyclophane series, with appreciably more distortion in [2.2] than in [3.3] paracyclophanes. Charge transfer interactions persist in triply and quadruply layered donor-acceptor paracyclophanes, but the orientation effects are lost. The charge transfer spectra of syn and anti diastereoisomers in the metacyclophane series are remarkably similar. Crystal structure analyses show considerable intramolecular distortion and mutual displacement, and non-parallelism of the donor and acceptor moieties. The ideas developed in the cyclophane studies are beginning to be applied to other areas of chemistry.