Structures and excitation energies of Zn-tetraarylporphyrin analogues: A theoretical study

The photophysical properties of beta-substituted Zn-tetraarylporphyrin (ZnTAP) analogues used as dyes in dye-sensitized solar cells were studied using density functional theory (DFT). Singlet-excitation energy calculations of ZnTAP analogues were performed using time-dependent DFT with B3LYP, B3PW91, PBEO exchange-correlation functionals at 6-31G(d) and 6-31+G(d) basis sets using B3LYP/6-31G(d) geometries. The PBEO functional at 6-31+G(d) basis set provided a better correlation with the experimental data for both B and Q-bands. The inclusion of solvation effect in the calculations provided a good agreement in terms of B:Q(ave) ratio of the oscillator strengths for both analogues with the experimental values. Analogue 2 has a higher and a more balanced charge-carrier transport rates than analogue 1. In general, the addition of an electron-donating group in the meso-substituent (analogue 2) resulted in a narrower band gap, higher oscillator strength, a more red-shifted absorption spectra, and better charge-transfer characteristics than analogue 1. (C) 2009 Elsevier B.V. All rights reserved