Theoretical study on the structures and electronic properties of oligo(p-phenylenevinylene) carboxylic acid and its derivatives: effects of spacer and anchor groups

Abstract

The structural parameters of oligo(p-phenylenevinylene)carboxylic acid (OPV3–COOH) and its derivatives were optimized using the density functionals B3LYP, M06, M06-HF, M06-2X and the MP2 method on 6-31G(d) basis set level. The results show that the structure from B3LYP calculation is more planar than from M06, M06-2X, M06-HF, and MP2, respectively. The structures of OPV3–COOH obtained from various methods were used to calculate the electronic properties by time-dependent density functional theory calculation with the TD-CAM-B3LYP/6-311G(d,p) including conductor polarizable continuum model solvation to compare with the experimental absorption bands of this molecule. The excitation energies from the coplanar structure using M06-2X/6-31G(d) (406 nm) are closer to the experimental absorption data (430 nm) than the data from geometries optimized by M06-HF/6-31G(d) (362 nm) and MP/6-31G(d) (382 nm). Therefore, in this study, the M06-2X/6-31G(d) method was selected to investigate the effects of spacers for the structures and the electronic properties of OPV3–COOH and some derivatives. Spacer groups such as thiophene, dithiophene and vinylenethiophene linking between chromophore and the cyanoacrylic acid (–CNCOOH) anchor group can increase the electron transfer and expand the π-conjugated system to shift the absorption band into the visible light region. The more extended electron transfer and the red-shift of the absorption band for OPV3–COOH and OPV3–CNCOOH derivatives are desirable for absorbing sunlight and good employing as photo-sensitizer in dye-sensitized solar cell. Thiophene (OPV3–Th–CNCOOH), dithiophene (OPV3–diTh–CNCOOH) and vinylenethiophene (OPV3–viTh–CNCOOH) as spacer lead to the expansion of the π-conjugated system and to bathochromically shifted absorption spectra. Therefore, the modeling of side chain, spacer and anchor group in this study suggests new sensitizer compounds that enhance the efficiency of electron transfer and absorption of the sunlight for new synthetic materials.