Open AccessDensity Functional Study of Tetraphenylporphyrin Long‐Range Exciton Coupling
Author(s) -
Moore Barry,
Autschbach Jochen
Publication year - 2012
Publication title -
chemistryopen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 29
ISSN - 2191-1363
DOI - 10.1002/open.201200020
Subject(s) - time dependent density functional theory , exciton , density functional theory , chromophore , tetraphenylporphyrin , chemistry , absorption spectroscopy , molecular physics , delocalized electron , circular dichroism , spectral line , computational chemistry , porphyrin , physics , photochemistry , crystallography , optics , condensed matter physics , quantum mechanics , organic chemistry
The performance of time‐dependent density functional theory (TDDFT) for calculations of long‐range exciton circular dichroism (CD) is investigated. Tetraphenylporphyrin (TPP) is used as a representative of a class of strongly absorbing chromophores for which exciton CD with chromophore separations of 50 Å and even beyond has been observed experimentally. A dimer model for TPP is set up to reproduce long‐range exciton CD previously observed for a brevetoxin derivative. The calculated CD intensity is consistent with TPP separations of over 40 Å. It is found that a hybrid functional with fully long‐range corrected range‐separated exchange performs best for full TDDFT calculations of the dimer. The range‐separation parameter is optimally tuned for TPP, resulting in a good quality TPP absorption spectrum and small DFT delocalization error (measured by the curvature of the energy calculated as a function of fractional electron numbers). Calculated TDDFT data for the absorption spectra of TPP are also used as input for a ‘matrix method’ (MM) model of the exciton CD. For long‐range exciton CD, comparison of MM spectra with full TDDFT CD spectra for the dimer shows that the matrix method is capable of producing very accurate results. A MM spectrum obtained from TPP absorption data calculated with the nonhybrid Becke88–Perdew86 (BP) functional is shown to match the experimental brevetoxin spectrum ‘best’, but for the wrong reasons.