PNNL

Abstract

meso-substituted tetrapyridyl porphyrins (free base, Ni(II), and Cu(II)) were investigated for their optical limiting (OL) capabilities using real-time (RT-), linear-response (LR-), and quadratic-response (QR-) time-dependent density functional theory (TDDFT) methods. These species are experimentally known to display a prominent reverse saturable absorption feature between the Q and B bands of the ground state absorption (GSA), which has been attributed to increased excited-state absorption (ESA) relative to GSA. A recently developed RT-TDDFT method19,29 for calculating ESA from a LR-TDDFT density was utilized with seven exchangecorrelation functionals (BLYP, PBE, B3LYP, PBE0, M06, BHLYP, and BHandH), and contrasted to calculations of ESA using QR-TDDFT with four exchange-correlation functionals (BLYP, B3LYP, BHLYP, BHandH). This allowed for comparison between functionals with varying amount of exact exchange (0-50%) as well as between the ability of RT-TDDFT and QR-TDDFT to reproduce OL behavior in porphyrin systems. The absorption peak positions and intensities for GSA and ESA are significantly impacted by the choice of DFT functional, with the most critical factor identified as the amount of exact exchange in the functional form. Calculating ESA with QR-TDDFT is found to be significantly more sensitive to the amount of exact exchange than GSA and ESA with RT-TDDFT, as well as GSA with LR-TDDFT. This is problematic when using the same approximate functional for calculation of both GSA and ESA, as the LR- and QR-TDDFT excitation energies will not have similar errors. Overall, the RT-TDDFT method reproduces the OL features for the systems studied here and is a viable computational approach for efficient screening of molecular complexes for OL properties.