ESTIMATION OF THE PROBABILITY-DISTRIBUTION OF END-GROUP DISTANCES OF CHAIN-LINKED ELECTRON-DONOR ACCEPTOR MOLECULES AND RADICAL-ION PAIRS -A MONTE-CARLO APPROACH

Probability distributions of center-to-center and edge-to-edge distanc es of chain-linked electron donor-acceptor molecules have been calcula ted applying a simple Monte-Carlo method. The donor is N,-dimethylanil ine, and the acceptor is pyrene. The linkages, in one study, are diffe rent flexible polymethylene chains, (CH2)n, with n = 5-16. In the syst ems with n = 5-1 0, the appearance of an odd-even effect in the calcul ated population of conformations of short distances below 10 angstrom correlates well with the fluorescence lifetimes measured recently. Mol ecules with a partly rigid chain, (CH2)n-trans-cyclohexane-(CH2)m, wit h n = 2, 3 and m = 2-4, were enclosed in the systematic investigation in order to find a molecule which, after generation of the radical ion pair by intramolecular electron transfer, would show a particularly n arrow distribution of the exchange interaction between the unpaired el ectron spins in the paramagnetic species. In the probability distribut ion of the compound with n = m = 3, virtually no conformations are obs erved at short distances if highly polar solvents are considered.