A TDDFT Study of the Fluorescence Properties of Three Alkoxypyridylindolizine Derivatives

The fluorescence properties of three pyridylindolizine derivatives (one tricarbomethoxy-7-pyridyl-pyrrolo-pyridine and two dicarboethoxy-3-bromobenzoyl-7-pyridyl-pyrrolopyridines) have been investigated by applying density functional theory (OFT) and the time-dependent OFT (TDDFT). Performances of two hybrid-type functionals (BH&HLYP and B3LYP) and one generalized gradient approximation (GGA) functional (PBE) as well as three basis sets (SV(P), DZP, and TZVP) have been assessed. The solvent environment has been modeled with the conductor-like screening model (COSMO). Of the three functionals only BH&HLYP is able to yield reasonable estimates for all the studied indolizine derivatives whereas the success of the PBE and B3LYP functionals is highly dependent on the structure of the studied molecule. The SV(P) basis set provides geometrical changes as well as fluorescence maxima and Stokes shifts that agree with those obtained with DZP and TZVP. When a nonpolar solvent is used, COSMO is able to reproduce the experimental fluorescence maxima and Stokes shifts well. However, the agreement between the calculations and experiments is not as good when a solvent with higher polarity is used.