Calculation of electronic spectra of porphin and its derivatives by a modified INDO/S method

• Published in: Journal of applied spectroscopy Vol. 75; no. 1; pp. 27 - 35
• Main Authors: Kuzmitsky, V. A., Volkovich, D. I.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 2008
• Subjects: Analytical Chemistry; Atomic/Molecular Structure and Spectra; Physics; Physics and Astronomy; quantum-chemical calculations; (INDO/Sm) parameterization; excited electron states; porphyrins; modified INDO/S method
• ISSN: 0021-9037; 1573-8647
• DOI: 10.1007/s10812-008-9016-7

Quantum-chemical calculations of excited electronic states of porphin (H 2 P) and Mg-porphin (MgP) have been carried out in the framework of the INDO/S method with varying off-diagonal matrix elements of the one-electron Hamiltonian {ie027-01} and electron-electron interaction integrals {ie027-02} as functions of the internuclear distance. It has been found that a simultaneous increase in the π-type overlap factor for {ie027-03} and decrease in the {ie027-04} integrals, as compared with {ie027-05} calculated by the Nishimoto-Mataga formula, make it possible to reproduce the positions of the Q-and B-transitions in the experimental absorption spectrum with a precision of ∼300 cm −1 . In this case, the N x -transition intensity of the H 2 P molecule is halved, which means that only two B-transitions should be related to the Soret band as in the four-orbital model. Using the proposed parameterization (INDO/Sm), electronic spectra have been calculated for a number of porphyrin compounds including chlorine, bacteriochlorin, tetrabenzoporphin, and tetraazaporphin. The results obtained agree with the experimental data to an accuracy of 300–700 cm −1 whereas the accuracy of the standard INDO/S calculation is no better than 3000 cm −1 .