Photophysics of 1-methyllumichrome

Sikorska, Ewa; Khemlinskii, Igor V.; Worrall, David R.; Williams, Siân L.; González‐Moreno, Rafael; Bourdelande, J. L.; Koput, Jacek; Sikorski, Marek

doi:10.1016/s1010-6030(03)00353-8

Cited by 17 publications

(10 citation statements)

References 32 publications

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“…With increasing polarity and proticity of the solvent a red shift of that band is observed. 13,14 For LC in water this shift even in all solvents. 17,21- 28 In theoretical work on isolated AL and LC, the optically dark 1 (np*) state is found to be below or degenerate with the optically bright 1 (pp*) state, presumably leading to a substantial radiationless decay of the 1 (pp*) population to the electronic ground state.…”

Section: Introductionmentioning

confidence: 93%

The photophysics of alloxazine: a quantum chemical investigation in vacuum and solution

Salzmann

Marian

2009

Photochem Photobiol Sci

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(Time-dependent) Kohn-Sham density functional theory and a combined density functional/multi-reference configuration interaction method (DFT/MRCI) were employed to explore the ground and low-lying electronically excited states of alloxazine, a flavin related molecule. Spin-orbit coupling was taken into account using an efficient, nonempirical mean-field Hamiltonian. Intersystem crossing (ISC) rate constants for S --> T transitions were computed, employing both direct and vibronic spin-orbit coupling. Solvent effects were mimicked by a conductor-like screening model and micro-hydration with up to six explicit water molecules. Multiple minima were found on the first excited singlet (S(1)) potential energy hypersurface (PEH) with electronic structures (1)(npi*) and (1)(pipi*), corresponding to the dark 1 (1)A'' (S(1)) state and the nearly degenerate, optically bright 2 (1)A' (S(2)) state in the vertical absorption spectrum, respectively. In the vacuum the minimum of the (1)(npi*) electronic structure is clearly found below that of the (1)(pipi*) electronic structure. Population transfer from (1)(pipi*) to (1)(npi*) may proceed along an almost barrierless pathway. Hence, in the vacuum, internal conversion (IC) between the 2 (1)A' and the 1 (1)A'' state is expected to be ultrafast and fluorescence should be quenched completely. The depletion of the (1)(npi*) state is anticipated to occur via competing IC and direct ISC processes. In aqueous solution this changes, due to the blue shift of the (1)(npi*) state and the red shift of the (1)(pipi*) state. However, the minimum of the (1)(npi*) state still is expected to be found on the S(1) PEH. For vibrationally relaxed alloxazines pronounced fluorescence and ISC by a vibronic spin-orbit coupling mechanism is expected. At elevated temperatures or excess energy of the excitation laser, the (1)(npi*) state is anticipated to participate in the deactivation process and to partially quench the fluorescence.

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Section: Introductionmentioning

confidence: 93%

The photophysics of alloxazine: a quantum chemical investigation in vacuum and solution

Salzmann

Marian

2009

Photochem Photobiol Sci

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“…Later, they studied the spectroscopical and photophysical properties of methyllumichrome and dimethyl-alloxazines absorbed on cellulose and in water, − and the acid–base properties of alloxazines and its methyl-substituted variants in their ground and first excited singlet states . In addition, they have explored singlet- and triplet-state properties of 1-methyllumichrome in a series of nonpolar, polar aprotic, and polar protic solvents, and in cellulose matrix; in the same time, they have explored solvent effects on the spectroscopic properties of lumiflavins and lumichromes and found that the former fluorescence quantum yield is one order larger than the latter due to their lower nonradiative rate constants . Recently, they employed time-resolved spectral and photon counting kinetic results to observe excited-state double proton transfer catalyzed by a carboxylic acid molecule hydrogen-bonded with alloxazines .…”

Section: Introductionmentioning

confidence: 99%

QM/MM Study on Mechanistic Photophysics of Alloxazine Chromophore in Aqueous Solution

et al. 2016

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Compared with isoalloxazine, the core chromophore of biologically important flavins, alloxazine exhibits much lower fluorescence quantum yield and larger intersystem-crossing quantum yield. However, its efficient radiationless relaxation pathways are still elusive. In this work, we have used the QM(MS-CASPT2//CASSCF)/MM method to explore the mechanistic photophysics of alloxazine chromophore in aqueous solution. On the basis of the optimized minima, conical intersections, and crossing points in the lowest 1ππ*, 1 nπ*, 3ππ*, and 3 nπ* states, we have proposed three energetically possible nonadiabatic relaxation pathways populating the lowest 3ππ* triplet state from the initially populated excited 1ππ* singlet state. The first is the direct 1ππ*→ 3ππ* intersystem crossing via the 1ππ*/3ππ* crossing point. The second is an indirect 1ππ* → 3ππ* intersystem crossing relayed by the dark 1 nπ* singlet state. In this route, the 1ππ* system first decays to the 1 nπ* state via the 1ππ*/1 nπ* conical intersection, followed by an 1 nπ*→ 3ππ* intersystem crossing at the 1 nπ*/3ππ* crossing point to arrive at the final 3ππ* state. The third is similar to the second one; but its intersystem crossing is relayed by the 3 nπ* triplet state. The 1ππ* system first decays to the 3 nπ* state via the 1ππ*/3 nπ* crossing point; the generated 3 nπ* state is then de-excited to the 3ππ* state through the 3 nπ*→ 3ππ* internal conversion at the 3 nπ*/3ππ* conical intersection. According to the classical El-Sayed rule, we suggest the second and third paths play a much more important role than the first one in the formation of the lowest 3ππ* state.

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“…The similarity in the structures of the AAs and FL also suggests the absorption of AA derivatives is also solvent-dependent. However, this effect is less pronounced in AAs (Figures and ) probably because of the fact that the conjugation in AAs is mainly within the benzopyrazine moiety and is thus less sensitive to the interactions with the amide moieties.…”

Section: Results and Discussionmentioning

confidence: 95%

“…For the AAs investigated, the emission is stronger in CH 3 OH than in other less polar solvents such as CH 2 Cl 2 and toluene, and there is a blue shift of ∼20 nm in CH 3 OH with respect to that in toluene. We attributed these two features to the AA–solvent interactions. , Specifically, intermolecular interactions, such as hydrogen bonds and π–π stacking, which are known to modulate the emission properties of a chromophore, can be formed with CH 3 OH and toluene. The impact of such interactions on the emission properties is also apparent for the emission of reference compounds, namely the FL and RFTA (Figure d,e).…”

Section: Results and Discussionmentioning

confidence: 99%

“…We attributed these two features to the AA−solvent interactions. 11,38 Specifically, intermolecular interactions, such as hydrogen bonds and π−π stacking, which are known to modulate the emission properties of a chromophore, can be formed with CH 3 OH and toluene. The impact of such interactions on the emission properties is also apparent for the emission of reference compounds, namely the FL and RFTA (Figure 3d,e).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Efficient Photooxidation of Sulfides with Amidated Alloxazines as Heavy-atom-free Photosensitizers

Guo

Xia

et al. 2020

ACS Omega

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Photooxidation utilizing visible light, especially with naturally abundant O 2 as the oxygen source, has been wellaccepted as a sustainable and efficient procedure in organic synthesis. To ensure the intersystem crossing and triplet quantum yield for efficient photosensitization, we prepared amidated alloxazines (AAs) and investigated their photophysical properties and performance as heavy-atom-free triplet photosensitizers and compared with those of flavin (FL) and riboflavin tetraacetate (RFTA). Because of the difference in the framework structure of AAs and FL and the introduction of carbonyl moiety, the absorption of FL at ∼450 nm is blue-shifted to ∼380 nm and weakened (ε = 8.7 × 10 3 for FL to ∼6.8 × 10 3 M −1 cm −1 ), but the absorption at ∼340 nm is red-shifted to ∼350 nm and enhanced by ∼50% (from ε = 6.4 × 10 3 for FL to ∼9.9 × 10 3 M −1 cm −1 ) in AAs. The intersystem crossing rates from the S 1 to T 1 are also enhanced in these AAs derivatives, while the fluorescence quantum yield decreases from ∼30 to ∼7% for FL and AAs, respectively, making the triplet excited state lifetime and the singlet oxygen quantum yield of AAs at least comparable to those of FL and RFTA. We examined the performance of these heave-atom-free chromophores in the photooxidation of sulfides to afford sulfoxides. In accordance with the prolonged triplet excited state lifetime and enhanced triplet quantum yield, 2−5-fold performance enhancements were observed for AAs in the photooxidation of sulfides with respect to FL. We proposed that the key reactive oxygen species of AA-sensitized photooxidation are singlet oxygen and superoxide radical anion based on mechanistic investigations. The research highlights the superior performance of AAs in photocatalysis and would be helpful to rationalize the design of efficient heavy-atom-free organic photocatalysts.

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Photophysics of 1-methyllumichrome

Cited by 17 publications

References 32 publications

The photophysics of alloxazine: a quantum chemical investigation in vacuum and solution

The photophysics of alloxazine: a quantum chemical investigation in vacuum and solution

QM/MM Study on Mechanistic Photophysics of Alloxazine Chromophore in Aqueous Solution

Efficient Photooxidation of Sulfides with Amidated Alloxazines as Heavy-atom-free Photosensitizers

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