DFT/MRCI calculations on the excited states of porphyrin, hydroporphyrins, tetrazaporphyrins and metalloporphyrins

Abstract

A combination of density functional theory and multi-reference configuration interaction methods (DFT/MRCI) has been applied to the calculation of electronic absorption spectra in a series of porphyrin-type molecules. The calculated excitation energies and oscillator strengths for free-base porphyrin (PH 2 ) are in excellent agreement with experiment for both lower and higher excited states which are characterized by a significant contribution of double excitations (b20%). The 4 1 B 2u , 4 1 B 3u , and 5 1 B 2u states are assigned to the L-band and the 7 1 B 3u state to the M-band. The results for the hydroporphyrins chlorin (CH 2 ) and bacteriochlorin (BH 2 ) are in agreement with the experimentally observed increase in intensity for the Q-bands relative to PH 2 . For BH 2 we predict a red shift of the Q x -band (0.2 eV) and a blue shift of the B-band (0.5-0.7 eV) in comparison to both PH 2 and CH 2 . For porphyrazine (PzH 2 ) and the commercial pigment phthalocyanine (PcH 2 ) the calculated oscillator strengths of the Qand B-bands are of comparable size explaining the intense color of PcH 2 . For the metalloporphyrins with magnesium (PMg) and zinc (PZn), the x-and y-polarized components of the Q-and B-bands collapse, due to the higher D 4h symmetry of the molecules. The calculations reproduce the slight, experimentally observed increase in the oscillator strength of the Q-band and the decrease for the B-band. These effects are ascribed to the electropositive nature of the metals relative to hydrogen. Except for the Q-bands, which are adequately described by the 'four-orbital model,' it is essential to account for excitations outside the four frontier orbitals as well as double and triple excitations for accurate reproduction of experimental data. We compare our results both with experiment and, where available, recent first-principle SAC-CI, MRMP, and TDDFT calculations.

Singlet and Triplet Excited States and Intersystem Crossing in Free‐Base Porphyrin: TDDFT and DFT/MRCI Study

“…Bond lengths are given in . energy of the 1 1 B 3u transition is about 0.3 eV higher than the energy of the Q x band-the first band in the vertical absorption spectra of FBP (1.98 eV [25] )-while at the same time the DFT/MRCI method gives an energy of 1.90 eV, which is lower than the observed experimental value by merely 0.08 eV.…”

“…In contrast, the TDDFT singlet transitions of np* type are stabilized by % 0.2 eV in comparison to the respective DFT/MRCI values. Comparison with experimental values shows that both TDDFT and DFT/MRCI methods predict reasonably accurate energies of the optically allowed transitions which contribute to the Q y and Soret bands (2.42 and 3.33 eV, respectively, in experimental vapor spectra [25] ). On the other hand, the calculated TDDFT Figure 1.…”

“…[17,18,[22][23][24][25] The TDDFT energies of most pp* excited singlet states are characterized by systematic upshifts of % 0.3 eV compared to the DFT/MRCI results. In contrast, the TDDFT singlet transitions of np* type are stabilized by % 0.2 eV in comparison to the respective DFT/MRCI values.…”

Dissociative electron attachment and electron energy-loss spectra of phenyl azide

“…This approach was shown to yield excellent electronic spectra of organic molecules at reasonable computational expense [13][14][15][16]. As AO basis we employ the aug-cc-VTZ (C, N) and cc-pVTZ (H) sets of Dunning [17,18] but with discarded f-function on carbon and nitrogen.…”

Structural, 103Rh NMR and DFT Studies of a Bis(phosphane)RhIII–Porphyrin Derivative

“…[19,20] Most studies on simple Rh complexes have therefore employed indirect detection [21] of the 103 Rh nucleus in double-or triple-resonance HMQC experiments by employing polarisation transfer from 31 P, 1 H or 11 B. [22] Given that the Rh III -porphyrins investigated hitherto [13,23] have not been probed by 103 Rh NMR spectroscopy, we describe here the first combined 103 Rh NMR and DFT study of a phosphane-ligated Rh III -porphyrin, namely [Rh(TPP)(PEtPh 2 ) 2 ]SbF 6 (1, Scheme 1).…”