Donor–Acceptor 1,4-Fluorenylene Chromophores: Photophysics, Electrochemistry, and Synthesis through a Route for Asymmetric Chromophore Preparation

摘要

Fourteen chromophores of the form 1-(4-X-styryl)-4-(4-nitrostyryl)benzene or 1-(4-X-styryl)-4-(4-nitrostyryl)fluorene have been synthesized with X = CF_3, Cl, I, H, CH_3, OCH_3, or OCH(CH_3)_3. An innovative synthetic route was developed in the course of this work wherein phosphonium-phosphonate ester bifunctional precursors were employed. By exploiting steric considerations and the difference in acidity of protons in the position alpha to the phosphonium and phosphonate ester, target asymmetric chromophores were assembled in a straightforward fashion with high selectivity. The photophysical characteristics of the chromophores are described, including notable solvatochromism revealed by measuring photophysical properties in acetonitrile, dichloromethane, tetrahydrofuran, and toluene. Electrochemical analysis by cyclic voltammetry, along with DFT calculations (B3LYP-6-31G*) were employed to reveal the HOMO and LUMO distributions and energies, thus providing further understanding of the properties of these materials and the similarities/ differences between phenylene-centered and fluorenylene-centered chromophores.