4.6 Article

Understanding Hyperporphyrin Spectra: TDDFT Calculations on Diprotonated Tetrakis(p-aminophenyl)porphyrin

Journal

JOURNAL OF PHYSICAL CHEMISTRY A
Volume 125, Issue 46, Pages 9953-9961

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.jpca.1c06621

Keywords

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Funding

  1. Research Council of Norway [262229, 324139]
  2. South African National Research Foundation [129270, 132504]

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A detailed TDDFT study was conducted on the effect of diprotonation on the UV-vis-NIR spectra of free-base tetraphenylporphyrin and tetrakis(p-aminophenyl)porphyrin. The study revealed that the redshift in the diprotonated forms can be explained by changes in molecular orbitals. Additionally, it was found that the hybrid B3LYP functional provided a better description of key spectral features compared to the pure OLYP functional.
A detailed TDDFT study (with all-electron STO-TZ2P basis sets and the COSMO solvation model) has been carried out on the effect of diprotonation on the UV-vis-NIR spectra of free-base tetraphenylporphyrin and tetrakis(p-aminophenyl)porphyrin. The diprotonated forms have been modeled as their bis-formate complexes, i.e., as so-called porphyrin diacids. The dramatic redshift of the Q-band of the TAPP diacid has been explained in terms of an elevated a(2u) HOMO and lowered LUMOs, both reflecting infusion of aminophenyl character into the otherwise classic Gouterman-type frontier MOs. The exercise has also yielded valuable information on the performance of different exchange-correlation functionals. Thus, the hybrid B3LYP functional was found to yield a substantially better description of key spectral features, especially the diprotonation-induced redshifts, than the pure OLYP functional. Use of the range-separated CAMY-B3LYP functional, on the other hand, did not result in improvements relative to B3LYP.

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