Effect of substitution on the optical properties and HOMO-LUMO gap of oligomeric paraphenylenes.

A series of dialkyl amino benzophenone dimers with various alkyl chain lengths is presented. Gaussian B3LYP/6-31G(d) calculations show that the band gap decreases within the dimer series as a function of the donor group efficiency. Theoretical calculations show that the interaction between phenyl-phenyl rings is more important than simple donor-acceptor effects. We report the experimental and electro-optical properties of one of these dimers, N,N-(dibutyl)-4-amino-benzophenone. The experimental and theoretical results enabled us to design a new dimer. Altogether, side chain substituents reported herein tune the theoretical band gap of paraphenylene based dimers by over 8.86 eV.