Specific photoreactions of flavanones typical of n,π* and π,π* characters in lowest triplet states

Matsushima, Ryoka; SAKAI, K.

doi:10.1039/p29860001217

Cited by 9 publications

(2 citation statements)

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“…On the other hand, linear relationships between both the lowest excited singlet and triplet energy levels, and the triplet decay constants of the parasubstituted phenylanilines and pirydineanilines were obtained, yet based only on 3 to 7 substituted derivatives . Quenching of emission spectra of substituted flavanones and the Hammett correlations enabled authors to propose mechanisms of competing photochemical processes in and to assign the relative n π* and ππ* contributions in the T 1 states …”

Section: Introductionmentioning

confidence: 96%

“…31 Quenching of emission spectra of substituted flavanones and the Hammett correlations enabled authors to propose mechanisms of competing photochemical processes in and to assign the relative nπ* and ππ* contributions in the T 1 states. 32 The nπ* triplet-state energies of ca. 60 substituted aroyls (acetophenones, benzaldehydes, benzophenones, and anthraquinones) were found to be increased by the electron-donating substituents while decreased by the electron-withdrawing substituents, and, except for anthraquinones, they were satisfactorily correlated with the Hammett constants.…”

Section: Introductionmentioning

confidence: 99%

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Substituent Effect in the First Excited Triplet State of Monosubstituted Benzenes

Dobrowolski

Karpińska

2020

ACS Omega

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The structure of 30 monosubstituted benzenes in the first excited triplet T1 state was optimized with both unrestricted (U) and restricted open shell (RO) approximations combined with the ωB97XD/aug-cc-pVTZ basis method. The substituents exhibited diverse σ- and π-electron-donating and/or -withdrawing groups. Two different positions of the substituents are observed in the studied compounds in the T1 state: one distorted from the plane and the other coplanar with a quinoidal ring. The majority of the substituents are π-electron donating in the first group while π-electron withdrawing in the second one. Basically, U- and RO-ωB97XD approximations yield concordant results except for the B-substituents and a few of the planar groups. In the T1 state, the studied molecules are not aromatic, yet aromaticity estimated using the HOMA (harmonic oscillator model of aromaticity) index increases from ca. −0.2 to ca. 0.4 with substituent distortion, while in the S1 state, they are only slightly less aromatic than in the ground state (HOMA ≈0.8 vs ≈1.0, respectively). Unexpectedly, the sEDA(T1) and pEDA(T1) substituent effect descriptors do not correlate with analogous parameters for the ground and first excited singlet states. This is because in the T1 state, the geometry of the ring changes dramatically and the sEDA(T1) and pEDA(T1) descriptors do not characterize only the functional group but the entire molecule. Thus, they cannot provide useful scales for the substituents in the T1 states. We found that the spin density in the T1 states is accumulated at the Cipso and Cp atoms, and with the substituent deformation angle, it nonlinearly increases at the former while decreases at the latter. It appeared that the gap between singly unoccupied molecular orbital and singly occupied molecular orbital (SUMO-SOMO) is determined by the change of the SOMO energy because the former is essentially constant. For the nonplanar structures, SOMO correlates with the torsion angle of the substituent and the ground-state pEDA(S0) descriptor of the π-electron-donating substituents ranging from 0.02 to 0.2 e. Finally, shapes of the SOMO-1 instead of SOMO frontier orbitals in the T1 state somehow resemble the highest occupied molecular orbital ones of the S0 and S1 states. For several planar systems, the shape of the U- and RO-density functional theory-calculated SOMO-1 orbitals differs substantially.

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Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%