Spectroscopic Properties of Porphyrin-Like Photosensitizers:  Insights from Theory

Abstract

Electronic absorption spectra of six porphyrin-like photosensitizers, porphyrin, chlorin, bacteriochlorin, pheophytin a, porphyrazin, and texaphyrin, have been calculated within the time-dependent DFT framework (TDDFT) in conjunction with the PBE0 hybrid functional. Energetic and orbital aspects are discussed by comparing systems together so as to assess the best molecules for photodynamic therapy applications. Excitation energies and oscillator strengths are found to be in good agreement with both experimental data and previous theoretical works. In particular, whereas significant discrepancies (0.3 eV) appear for Qx bands, results become more reliable as wavelengths decrease. To elucidate the effect of the local environment, we have taken into account solvation either with explicit water molecules interacting via hydrogen bonds with the system or with a continuum model (C-PCM). The supramolecular approach does not affect spectra, while using C-PCM improves Qx and B band values and strengthens intensities significantly. In both gaseous and aqueous phases, texaphyrin, pheophytin a, and bacteriochlorin Qx bands are found in the 600-800 nm range as expected by experimental works. These data are particularly interesting in the perspective of systematic studies of other photosensitizers and should make experimentalists' works easier.

A quantum chemical study on the free radical scavenging activity of tyrosol and hydroxytyrosol

“…TD-DFT efficiently and rapidly provides transition energies for mono-determinental systems in both gas and condensed phases [111]. Moreover, it has been demonstrated that he UV-vis spectra obtained from this approach frequently agree with experiments [112][113][114][115][116].…”

Electronic structures and spectra of porphyrin with fused benzoheterocycles: DFT and TDDFT‐PCM investigations

“…The experimental absorption spectra of QP, BTDP, and BXDP were measured in chloroform. Because of their highly conjugated macrocycles, porphyrin-like systems exhibit intense absorption around 400 nm, the so-called B-bands, followed by weaker absorption band between 500 and 800 nm, known as Q-bands [32][33][34]. Their spectral characters can be interpreted by means of the four orbital Gouterman's model on the whole, where the principal excitations involve the two highest occupied molecular orbitals (MOs) (HOMO and HOMO-1) and the two lowest unoccupied molecular orbitals (LUMO and LUMOϩ1) [35,36].…”

Alternative selection rules for one- and two-photon transitions in tribenzotetraazachlorin: Quasi-centrosymmetrical π-conjugation pathway of formally non-centrosymmetrical molecule

“…Taking into account configurational interaction (CI) in the relative molecule, i.e., free-base porphyrazine, at the CNDO/S 53 and TDDFT 54 levels of theory also predicts that the lowest gg transition with non-vanishing 2PA strength is of the A g → A g type. The authors 53,54 also found that the one-electron approximation works quantitatively for this particular transition in porphyrazine. Therefore, we assume the A g → A g symmetry for the lowest energy 2PA-allowed transition in both H 2 TtBuPc and H 2 TBTAC.…”