Phosphole-containing pi-conjugated systems: From model molecules to polymer films on electrodes

Two series of 2.5-dipyridyl and 2.5-dithienylphosphole derivatives containi ng sigma (3)- or sigma (4)-P atoms were prepared. and their optical (UV/Vis absorption, fluorescence spectra) and electrochemical properties were syst ematically evaluated. These physical properties depend mainly on the nature s of the 2.5-substituents and of the phosphorus moiety, and they revealed t hat these compounds contain extended pi- conjugated systems. Structure -pro perty relationships were established on the basis of these experimental dat a and ab initio calculations on the parent molecules. The limited aromatic character and low-lying LUMO of the phosphole ring appear to be crucial for achieving a highly delocalised pi system. Electrooxidation of 2,5-dithieny lphosphole derivatives affords electroactive films with low optical band ga ps. As observed for the corresponding monomers, the optical and electrochem ical properties of the polymers can be varied over a wide range by modifyin g the nature of the phosphorus moiety.