Optical signatures of borico dyes: a TD-DFT analysis

Why do TD-DFT excitation energies of BODIPY/Aza-BODIPY families largely deviate from experiment? Answers from electron correlated and multireference methods

The vertical excitation energies of 17 boron-dipyrromethene (BODIPY) core structures with a variety of substituents and ring sizes are benchmarked using time-dependent density functional theory (TD-DFT) with nine different functionals combined with the cc-pVTZ basis set. When compared to experimental measurements, all functionals provide mean absolute errors (mean AEs) greater than 0.3 eV, larger than the 0.1-0.3 eV differences typically expected from TD-DFT. Due to the high linear correlation of TD-DFT results with experiment, most functionals can be used to predict excitation energies if corrected empirically. Using the CAM-B3LYP functional, 0-0 transition energies are determined, and while the absolute difference is improved (mean AE = 0.478 eV compared to 0.579 eV), the correlation diminishes substantially (R(2) = 0.961 to 0.862). Two very recently introduced charge transfer (CT) indices, q(CT) and d(CT), and electron density difference (EDD) plots demonstrate that CT does not play a significant role for most of the BODIPYs examined and, thus, cannot be the source of error in TD-DFT. To assess TD-DFT methods, vertical excitation energies are determined utilizing TD-HF, configuration interaction CIS and CIS(D), equation of motion EOM-CCSD, SAC-CI, and Laplace-transform based local coupled-cluster singles and approximate doubles LCC2* methods. Moreover, multireference CASSCF and CASPT2 vertical excitation energies were also obtained for all species (except CASPT2 was not feasible for the four largest systems). The SAC-CI/cc-pVDZ, LCC2*/cc-pVDZ, and CASPT2/cc-pVDZ approaches are shown to have the smallest mean AEs of 0.154, 0.109, and 0.100 eV, respectively; the utility of the LCC2* approach is demonstrated for eight extended BODIPYs and aza-BODIPYs. We found that the problems with TD-DFT arise from difficulties in dealing with the differential electron correlation (as assessed by comparing CCS, CC2, LR-CCSD, CCSDR(T), and CCSDR(3) vertical excitation energies for five compounds) and from contributions of multireference character and double excitations (from analysis of the CASSCF wave functions).

Effect of alkyl substituents in BODIPYs: a comparative DFT computational investigation

A detailed computational investigation encompassing the effects of alkyl groups on the structural and electronic properties of BODIPY dyes is presented.

Solvatochromism of BODIPY-Schiff dye

A boron-dipyrrin chromophore connected with an o-hydroxyaryl aldimine by a diazo bridge (BODIPY-Schiff dye) has been developed. The photophysical properties of the BODIPY-Schiff dye have been investigated with UV, steady-state, and time-resolved fluorimetry. The spectral features have been characterized with respect to density functional theory and time-dependent density functional theory. The conformational analysis of the studied compound has been accomplished both in the ground and excited states. A scheme of the processes occurring in the BODIPY-Schiff dye has been proposed.

Vibronic spectra of organic electronic chromophores

Vibronic effects in organic electronic building blocks are presented.