Franck-Condon simulation of vibrationally resolved optical spectra for zinc complexes of phthalocyanine and tetrabenzoporphyrin including the Duschinsky and Herzberg-Teller effects

Abstract

High resolved absorption and fluorescence spectra of zinc complexes of phthalocyanine (ZnPc) and tetrabenzoporphyrin (ZnTBP) in the region of Q states were reported. Few theoretical investigations were performed to simulate the well-resolved spectra and assigned the vibrational bands of the large molecules, especially for high symmetrical characteristic molecules, on account of the difficulties to optimize the excited states and analyze a large number of final vibrational-normal modes. In the present work, the S(0) ↔ S(1) absorption and fluorescence spectra (that is, the Q band) of ZnPc and ZnTBP were simulated using time-dependent density functional theory with the inclusions of Duschinsky and Herzberg-Teller contributions to the electronic transition dipole moments. The theoretical results provide a good description of the optical spectra and are proved to be in excellent agreement with experimental spectra in inert-gas matrices or in supersonic expansion. This study focused attentions on the optical spectral similarities and contrasts between ZnPc and ZnTBP, in particular the noticeable Duschinsky and Herzberg-Teller effects on the high-resolved absorption and fluorescence spectra were considered. Substitution of meso-tetraaza on the porphyrin macrocycle framework could affect the ground state geometry and alter the electron density distributions, the orbital energies that accessible in the Q band region of the spectrum. The results were used to help interpret both the nature of the electronic transitions in Q band region, and the spectral discrepancies between phthalocyanine and porphyrin systems.

CASSCF-based explicit ligand field models clarify the ground state electronic structures of transition metal phthalocyanines (MPc; M = Mn, Fe, Co, Ni, Cu, Zn)

“…These uncontentious assignments are unanimously supported in the literature. [18,53,28,64,65,66,67,68,69,70,71,72,73,74,75,76,18] For CuPc, inspection of Figure 2 suggests that an alternative configuration may be possible, with two electrons in the d z 2 orbital and only one in the ligand HOMO, which would correspond to a closed-shell metal cation surrounded by a radical anion ligand. However, this physically implausible state is higher in energy than the depicted configuration, both because the d x 2 −y 2 orbital is less stable than the ligand HOMO and because it is harder to pair electrons within the more compact metal-centred orbital.…”

Ground and excited states of zinc phthalocyanine, zinc tetrabenzoporphyrin, and azaporphyrin analogs using DFT and TDDFT with Franck-Condon analysis

“…18,25,27 Recently, these molecules along with a copper center and asymmetric analogs have been synthesized and investigated with magnetic circular dichroism (MCD) theory. 28 In fact, there is a large amount of investigation of MPcs over the last couple of decades by Mack, Stillman, and Kobayashi.…”

“…19,20,[28][29][30] However, there has been minimal research presented on these molecules using Franck-Condon analysis until a recent study by Gou et al presented work on ZnPc and ZnTBP. 27 Two approaches seem to have dominated the theoretical work. One uses a combination of density functional theory (DFT), TDDFT, and oscillator strengths (intensities) of excitation energies.…”

Vibrationally Resolved Absorption and Fluorescence Spectra of Firefly Luciferin: A Theoretical Simulation in the Gas Phase and in Solution

“…The previous theoretical studies also reported its absorption and fluorescence maxima . It is necessary to provide the vibrationally resolved spectra of firefly luciferin for the further study of firefly bioluminescence because: (1) the spectra shape can be affected by adding the consideration of vibrational excitations ; (2) it is helpful to understand the photophysical and photochemical properties by assigning the vibronic transitions corresponding to the different peaks of spectra ; and (3) the different Franck–Condon (FC) factors of vibronic transitions reflect molecular structure information .…”