Two‐colour pulsed Raman studies of the lowest excited singlet state of tetraphenylporphyrin: band assignments and electronic structure

Bell, Steven E. J.; Hegarty, J.; Morvan, Fabrice

doi:10.1002/(sici)1097-4555(200004)31:4<289::aid-jrs541>3.3.co;2-h

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“… c There were minor differences in band position in refs and , but for the purposes of this paper, the key parameters are the shifts on excitation to the triplet state. So values for the ground state obtained along with the triplet values are preferred here.…”

Section: Resultsmentioning

confidence: 96%

“…The experimental resonance Raman spectra for ground state (S 0 ) na H 2 TPP and its d 2 , d 8 , d 10 , d 20 , d 22 , and 13 C 4 isotopomers were published previously 11 along with the corresponding triplet state (T 1 ) data. In subsequent work on the excited singlet states of these isotopomers, some additional ground state bands were assigned. Table compares the observed vibrational frequencies taken from refs and with the scaled frequencies from our calculations.…”

Section: Resultsmentioning

confidence: 99%

“…In subsequent work on the excited singlet states of these isotopomers, some additional ground state bands were assigned. Table compares the observed vibrational frequencies taken from refs and with the scaled frequencies from our calculations. For the sake of brevity, we have not included in Table any calculated bands for which we have no experimental data, but a fuller listing is available in the Supporting Information.…”

Section: Resultsmentioning

confidence: 99%

“…So values for the ground state obtained along with the triplet values are preferred here. Only those bands not originally assigned are taken from ref .…”

Section: Resultsmentioning

confidence: 99%

“…13 We have previously published extensive TR 3 investigations on the S 0 , S 1 , and T 1 states of natural isotopic abundance (na) H 2 TPP along with several of its isotopomers; see Figure 1 for the nomenclature of the isotopomers investigated. 10,11,14 Even though the spectra obtained were complex, containing numerous overlapping bands, several bands in the spectra were assigned by using expected shifts on isotopic substitution and/or excitation. There is a need for well-established assignments because, if we are to use the changes in vibrational frequency to understand the structural changes which accompany excitation, the assignments must be reliable, not least because the number of bands which give information useful for this procedure is small.…”

Section: Introductionmentioning

confidence: 99%

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DFT Studies of the Resonance Raman Spectra of Ground and Excited Triplet State Free Base meso-Tetraphenylporphyrin (H₂TPP)

Oakes

Bell

2003

J. Phys. Chem. A

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DFT calculations at the B3LYP/6-31G(d) level were carried out for the ground and excited triplet states of free base meso-tetraphenylporphyrin, H2TPP, and its d 2, d 8, d 10, d 20, d 22, and 13C4 isotopomers. The agreement between experimental and calculated (scaled with a single factor of 0.973) band positions for the ground state was acceptable (rms = 9.9 cm-1). In addition, although the shifts on isotopic substitution were frequently of the same order as this rms error in the absolute positions, it was found that the cancellation of errors in the calculations meant that the direction and magnitude of even small isotope shifts < 10 cm-1 were also calculated correctly. In the D 2 symmetry of the calculations the lowest lying triplet state corresponded to a one-electron transition from the b1 HOMO to a b3 LUMO. It was found that the calculated changes in cm-1 of the vibrational modes on excitation to this triplet (ΔS - T) reproduced the ΔS - T values of the seven bands found in the experimental spectra. Three of these bands (ν2, ν1 2, and ν15) moved to lower cm-1 on excitation, two were essentially unchanged (φ4 and ν1), and two moved to higher cm-1 ( ν4 and ν6). Since the ΔS - T values are typically small (≤10's of cm-1), the correct prediction of the pattern of small shifts associated with population of an excited state with a particular electronic configuration is impressive. As before, this improved accuracy presumably arises because errors in the calculations of absolute positions cancel when values for the same modes in different electronic states are subtracted to give shifts on excitation. This level of accuracy is necessary if ΔS - T values are to be used to assign orbital parentage. Surprisingly, for several of the modes the calculated ΔS - T shifts differed dramatically between isotopomers. For example, for ν2: ΔS - T(calc), d 0 = −5 cm-1, d 8 = −30 cm-1; Δ S - T(obs), d 0 = −15 cm-1, d 8 = −26 cm-1. These differences were found to reflect not only the changes in force constants due to promotion to the triplet state (which are the same irrespective of which isotopomer is under consideration) but also changes in the mode composition on excitation which alters the isotope sensitivity. In the case of H2TPP, the mode compositions change because excitation from b1 → b3 orbitals accentuates the difference in bonding between the pairs of protonated and unprotonated pyrrole rings. In effect, excitation increases the rectangular distortion that is already present in the ground state of free base porphyrins and which distinguishes them from more regular D 4 h (square) metalloporphyrins. The further distortion causes modes that in the more regular systems involve all four of the pyrrole rings to become increasingly localized on just the protonated or unprotonated pyrroles. More generally, the success of the DFT calculations at this level of theory in predicting frequency shifts on excitation for an extensive series of isotopomers clearly validates the approach. Interpretation of the resonance Raman spectra of t...

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Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…So values for the ground state obtained along with the triplet values are preferred here. Only those bands not originally assigned are taken from ref .…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

DFT Studies of the Resonance Raman Spectra of Ground and Excited Triplet State Free Base meso-Tetraphenylporphyrin (H₂TPP)

Oakes

Bell

2003

J. Phys. Chem. A

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Two‐colour pulsed Raman studies of the lowest excited singlet state of tetraphenylporphyrin: band assignments and electronic structure

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DFT Studies of the Resonance Raman Spectra of Ground and Excited Triplet State Free Base meso-Tetraphenylporphyrin (H₂TPP)

DFT Studies of the Resonance Raman Spectra of Ground and Excited Triplet State Free Base meso-Tetraphenylporphyrin (H₂TPP)

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Two‐colour pulsed Raman studies of the lowest excited singlet state of tetraphenylporphyrin: band assignments and electronic structure

Cited by 1 publication

References 0 publications

DFT Studies of the Resonance Raman Spectra of Ground and Excited Triplet State Free Base meso-Tetraphenylporphyrin (H2TPP)

DFT Studies of the Resonance Raman Spectra of Ground and Excited Triplet State Free Base meso-Tetraphenylporphyrin (H2TPP)

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DFT Studies of the Resonance Raman Spectra of Ground and Excited Triplet State Free Base meso-Tetraphenylporphyrin (H₂TPP)

DFT Studies of the Resonance Raman Spectra of Ground and Excited Triplet State Free Base meso-Tetraphenylporphyrin (H₂TPP)