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Theoretical study of internal conversion between excited states of a functionalized porphyrin

Date: Thursday January 13, 2022 - 15.00
Streaming at: https://global.gotomeeting.com/join/549695205
Speaker: Pavel Rukin (S3 Istituto Nanoscienze CNR)

Title: Theoretical study of internal conversion between excited states of a functionalized porphyrin

Abstract: Porphyrins can be used as candidates for synthesizing various efficient bioinspired molecular systems. Therefore it is very important to know its photophysical properties for the proper engineering. The nature of internal conversion (IC) between excited states in porphyrin is still an open question. We do this study to come closer to the answer. For this purpose 5-Ethoxycarbonyl-10-mesityl-15-carboxymethylbenzene porphyrin (1P) [1] is investigated using DFT and TDDFT with the range-separated hybrid CAM-B3LYP functional and the 6-311G(d,p) basis set. The solvent effects (THF) are taken into account within the polarized continuum model.
In addition to the excited states referred to classical Gouterman four-orbital model this study takes into account two additional dark states. One of them has similar orbital nature as the lowest dark state in case of the bare porphyrin [2]. However, another one is particular for 1P and involves the orbital on the substituent. It is shown that both of these states have intersection with the states of the B band.
Active normal modes that contribute IC due to vibrational relaxation are defined by Huang-Rhys factors (HR) analysis [3]. Trajectory analysis along the active normal modes in the basis of the 1st excited state was carried out. Each snapshot of the trajectory consists the information of:

  1. Energy level diagram with the oscillator strength of each level
  2. Composition of orbitals involved in the transitions to the excited states
  3. Transition dipole moments between the ground state and the excited states
This analysis in addition to HR one clarifies the contribution of active modes into transitions between the excited states. Moreover the trajectory scans allow detecting possible conical intersections or avoided crossings.

[1] Y. Terazono, G. Kodis, M. Chachisvilis, B. R. Cherry, M. Fournier, A. Moore, T. A. Moore, and D. Gust, Multiporphyrin Arrays with π-π Interchromophore Interactions. J. Am. Chem. Soc. 2015, 137(1), 245–258.
[2] K. Falahati, C. Hamerla, M. Huix-Rotllant, and I. Burghardt, Ultrafast photochemistry of free-base porphyrin: A theoretical investigation of B→Q internal conversion mediated by dark states. Phys. Chem. Chem. Phys. 2018, 20, 12483–12492.
[3] P. S. Rukin, A. Y. Freidzon, A. V. Scherbinin, V. A. Sazhnikov, A. A. Bagaturyants, and M. V. Alfimov M. V. Vibronic bandshape of the absorption spectra of dibenzoylmethanatoboron difluoride derivatives: analysis based on ab initio calculations. Phys. Chem. Chem. Phys. 2015, 17, 16997.

Host: Massimo Rontani massimo.rontani@nano.cnr.it

[Ultimo aggiornamento: 04/01/2022 13:21:48]