Syntheses and Properties of Donor−Acceptor-Substituted Molecules with a Bicyclo[2.2.1]heptane, a Bicyclo[2.2.2]octane, and a Tricyclo[3.3.0.03,7]octane Spacer

Starting from bicyclo[2.2.1]heptane-2,5-dione, bicyclo[2.2.2]octane-2,5-dione and tricyclo[3.3.0.03,7]octane-2,6-dione we were able to synthesize donor−acceptor-substituted derivatives by condensation reactions. The components for the condensations were propanedinitrile (21) for the acceptor part, and diethyl [(naphthalen-1-yl)methyl]phosphonate (12), diethyl [(anthracen-9-yl)methyl]phosphonate (13), and diethyl [(pyren-1-yl)methyl]phosphonate (14). To condense propanedinitrile we used the Knoevenagel condensation and for the phosphonates we used the Wittig−Horner−Emmons procedure. By means of NOESY NMR experiments the (E) configuration at the exo double bond of the donor−acceptor-substituted bicycles could be established. X-ray investigations on 22, 24, 27, and 39 confirmed the (E) configuration at the exo double bond and yielded the molecular parameters. Fluorescence spectra provided evidence for efficient photoinduced electron transfer in only the naphthalene and pyrene derivatives 22 and 26, but not in the analogous anthracene derivative 24 in accordance with estimates for ΔGet.