Electron delocalization in homoconjugated 7,7-diarylnorbornane systems: a computational and experimental study

A joint computational–experimental study has been carried out to analyze the homoconjugative interactions in 7,7‐diarylnorbornane (DPN) derivatives. The experimentally observed new bands in their UV/Vis have been accurately assigned by means of TD‐DFT calculations. Both experimental data and computations show that aromatic homoconjugation in acyclic systems is an effective mechanism for electron delocalization that resembles the situation described for polyphenylenes and polyenes. The effective homoconjugation length in homoconjugated oligomers is in the range of 6–7 aryl rings. The effect of substituents directly attached to the para carbon atom of the DPN moiety have been also studied. We found that the HOMO→LUMO vertical transitions can indeed be modified by the nature of the aromatic substituents in order to provoke dramatic changes in the electronic properties (i.e., in the absorption spectra) of the studied species.