Charged Push−Pull Polyenes in Solution: Anomalous Solvatochromism and Nonlinear Optical Properties

The linear and nonlinear optical properties of charged push−pull polyenes (CPPP) are, respectively, of interest in connection with unusual linear spectroscopic solvatochromic behavior in solution and other polar media and applications ranging from second harmonic generation to imaging and probing of biological systems. The CPPP are charged conjugated quasi-one-dimensional molecules containing an electron-donating group (D) and an electron-acceptor group (A) interacting via a π-conjugated bridge. Here we present a theoretical description for photoinduced charge transfer for such molecules in solution, based on a two valence bond state electronic description together with inclusion of a geometrical coordinate for the bridge and a solvent coordinate describing nonequilibrium solvation of the molecule. The theory both accounts for the anomalous linear solvatochromic behavior and provides a treatment of CPPP nonlinear optical properties in solution.