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The conformation distortion from the perpendicular conformation of the ground state to the approximately planar conformation of the excited state realizes the structural matching and reduce ΔEst between the excited states and promotes the electronic and vibration coupling between the singlet state and the triplet state. The dual emission of TADF and RTP of NISPh are expectedly observed. This universal conformational distortion charge transfer (CDCT) strategy undoubtedly opens a new avenue to develop novel high-performance purely organic light-emitting materials. [Display omitted] • The dual emission of thermally activated delayed fluorescence and room temperature phosphorescence of NISPh are observed. • The non-adiabatic conformation distortion promotes the electronic and vibration coupling between the excited state. • The conformational distortion charge transfer opens a new avenue to develop high-performance purely organic light-emitting materials. In this work, we report for the first time that thiophenol-substituted naphthalimide can achieve thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) simultaneously through non-conjugated flexible connection. Herein, we explain that the enhancement of intersystem crossing (ISC) between the singlet excited state and triplet excited states in NISPh is mainly caused by the non-adiabatic conformation distortion charge transfer (CDCT) of the excited states. More precisely, CDCT results in the conformation matching and energy barrier decrease between the excited states. In addition, the electronic and vibration coupling is further enhanced in NISPh. Our work substantiates a rational design strategy for the development of simple purely organic materials to achieve dual emission of TADF and RTP. [ABSTRACT FROM AUTHOR]

• Hydrogen bond effect on excited state for ITX in different solvents. • Models of ITX complexes of single and double hydrogen bonds were discussed. • Hydrogen bonding inhibits molecular vibration and eliminates self-quenching. In this work, the hydrogen bond effect on excited state mechanism of 2-isopropyl thioxanthone has been investigated in protic solvents by spectroscopic and computational chemistry methods. The two models of single hydrogen bond and double hydrogen bond provide the basis for the photophysical properties of ITX-solvent complexes, and the study of excited state hydrogen bond provides a theoretical basis for the emission of singlet and triplet states of ITX. We demonstrated that the intermolecular hydrogen bond C O⋯H O between ITX and protic solvents are significantly strengthened in the electronically excited-state upon photoexcitation of the ITX hydrogen-bonded complexes. Interestingly, hydrogen bonding inhibits molecular vibration and eliminates self-quenching and atmospheric oxygen quenching, which effectively inhibits non-radiative processes and improves the efficiency of emission. All the calculated spectral features are in good agreement with the spectral results recorded in experiments. This demonstrates that the ground state and excited state of the hydrogen-bonded ITX complexes presented here can well delineate in different solvents. This work provides a theoretical basis for the further development of the application of thioxanthone compounds. [ABSTRACT FROM AUTHOR]

[Display omitted] • Apigenin, Luteolin and Steppogenin were used as sunscreens to study in solution. • Site-selective electron transfer in the excited state is induced by hydrogen bond. • A certain theoretical basis for the application of plant flavonoids in sunscreen cosmetics. • This work clarified the excited state kinetic behavior of Apigenin, Luteolin and Steppogenin in solvent. In this present work, we have successfully designed and investigated three flavonoid sunscreen compounds. Based on steady-state spectroscopy and time-dependent density functional theory (TDDFT), the mechanism of excited state intramolecular proton transfer (ESIPT) of sunscreen compounds was studied. The calculated UV–vis absorption spectra and fluorescence emission spectra are in good agreement with the experimental results in methanol solution. The potential energy curve demonstrates that the ESIPT process can easily occur in the three sunscreen compounds without energy barrier. Therefore, the absorbed excitation energy can get back to the ground state through a non-radiative relaxation process. Light stability tests ensure that the three flavonoids have the potential as sunscreens. This work provides not only an application of the ESIPT process in sunscreen mechanisms, but also a theory basis for the development of novel sunscreen molecules. [ABSTRACT FROM AUTHOR]

In this work, we presented a theoretical investigation of single-triplet excited state transition process by the energy gap (Δ E ST) and spin-orbit coupling (SOC) for a series of novel designed anthraquinone compounds in solution. The molecular conformation, steady-state spectra and molecular orbitals were performed by quantum chemistry calculations to investigate the substituent effects on the Δ E ST and SOC and single-triplet state transition process. The molecular conformation gradually change from the planar of the ground state to torsion, which reduced the orbital overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). It was further demonstrated that the Δ E ST and SOC remarkably depend on substituents with different conjugation and the presence of benzene in the donor units in solution. The change of Δ E ST from 1.80 eV to 0.70 eV and SOC from 0.495 cm−1 to 5.127 cm−1. Furthermore, it was confirmed that the presence of benzene ring and the enhancement of conjugation in the donor substituent can reduce the Δ E ST and enhance the SOC in different anthraquinone compounds. This work paves a way for an understanding of the single-triplet excited state transition process controlled by Δ E ST and SOC characters of these kinds of anthraquinone compounds in solution. • Single-triplet excited states for novel designed anthraquinone compounds were investigated in solution. • Molecular conformation, steady-state spectra and molecular orbitals were calculated in solution. • Photophysical properties of different compounds depend on molecular conformational changes in excited states. • Energy gap (Δ E ST) and spin-orbit coupling (SOC) remarkably was regulated by different substituents in the donor units. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel synthetic routes toward ABTS by a good methods from the same raw material. • This work clarified the nature of excited states of ABTS in different oxidation states. • The relationship between the electronic structures and photochemistry of different oxidation states ABTS. • This work deepen understanding of the photophysical properties of ABTS materials. The molecular structures of 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), were calculated by using time-dependent density functional theory (TDDFT) model with M062X method with 6-311G (d, p) basis set. In this work, the ABTS were theoretically investigated from the geometric structure, the energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), the energy level gap Δ E HOMO-LUMO of the molecular ground state, excited stated properties and the electronic absorption spectra of different oxidation states. We studied the energy levels of LUMO and HOMO of ABTS in different oxidation states. Frontier molecular orbital analysis can provide insight into the nature of excited states. ABTS was synthesized from N -ethylamine by total synthesis. Then, we measured the UV–Vis spectra of ABTS before and after being oxidized by K 2 S 2 O 8. The calculated electronic structures and photochemical properties of different oxidation state of ABTS were in accordance with the experimental result. This work demonstrates the relationship between the electronic structures and photochemistry of different oxidation states ABTS hence paves the way for the rationally synthesis and deepen understanding of the photophysical properties of ABTS materials. [ABSTRACT FROM AUTHOR]

In this work, the effects of conformation torsion in the ground and excited states on the electronic structure, intramolecular hydrogen bonding and solvent effects on photophysics of donor-acceptor (D-A) molecules were investigated. We designed two heavy-atom-free molecules with carbazole (Cz) as donor as well as benzophenone (BP) and 3-benzoylpridine (BPy3) as acceptors. It comes out that both of the two molecules BP-Cz and BPy3-Cz have similar conformational torsion trending from planarization to verticalization and then to planarization, when they change from the ground state to the singlet excited state to the triplet excited state. The difference is that BPy3-Cz forms intramolecular hydrogen bond in the ground state, causing the photophsical properties have significant changes compared with BP-Cz. In the ground state, the configuration of BPy3-Cz is restricted by the weak hydrogen bond. The hydrogen bond is broken in the singlet excited state and then re-formed in the triplet excited state constituting a switch with the state change of "formation-breaking-reformation". In addition, the calculated UV absorption and phosphorescence spectra are approximate while the fluorescence spectrum of BPy3-Cz has a significant red shift which is induced by the lower excited state energy gap. One can note that the solvation spectra are blue-shifted due to the increased viscosity inhibiting the molecular rotation. Besides, the SOC constant (ξ) of two molecules are larger in the more planar triplet excited state rather than singlet excited state, indicating the possibility of LPL. The ξ sum change of BPy3-Cz portends long persistent luminescence. Thus, this work demonstrates that adjustable photochemical properties can be achieved by conformational torsion, which provides a new strategy for the study of molecular system design. Unlabelled Image • Conformation torsion effects of BP-CZ and BPy3-CZ in different states were investigated. • Configuration of BPy3-Cz could be limited after the formation of weak N···H hydrogen bonds. • A Hydrogen bond in BPy3-Cz forms a switch in different states of "formation-breaking-reformation". • SOC constant (ξ) sum change of BPY3-CZ portends long persistent luminescence. [ABSTRACT FROM AUTHOR]

In this work, we reported a coordination-promoted photoluminescence (CPPL) phenomenon of a new organometallic complex tBu(ONO)-W formed by ligand tBu(ONO) and metal tungsten for the first time. At the same time, the photoluminescence mechanisms of both the ligand tBu(ONO) and organometallic complex tBu(ONO)-W were investigated by using the steady-state and time-resolved spectroscopies as well as the time-dependent density functional theory (TDDFT) method. It was demonstrated that the weak photoluminescence of ligand tBu(ONO) could be ascribed as the destroyed planarity after significant configuration twisting in the excited state. However, the formation of the coordination bond between tBu(ONO) and the metal tungsten in the complex changes the two twisted parts of tBu(ONO) into a nearly planar configuration. The excited state configuration has a slight configuration change while the coplanarity of tBu(ONO)-W has not been destroyed. Therefore, the photoluminescence of tBu(ONO)-W is significantly enhanced compared to the ligand tBu(ONO). It can be proved that the coordination effect between the ligand and the metal inhibits the configuration twisting of tBu(ONO) and then promotes light emission. Moreover, it was also found that the emission peaks of tBu(ONO)-W are mainly originated from the relaxation of the ILCT and LMCT states. The experimental and theoretical results clearly show that the regulation of metal-ligand coordination bonds on the photoluminescence performance provides a new strategy for designing new high-performance luminescent materials. Image 1 • A coordination-promoted photoluminescence (CPPL) phenomenon of a new organometallic complex tBu(ONO)-W was reported. • The coordination effect inhibits the configuration twisting of tBu(ONO) and then promotes light emission of complex. • The emission peaks of tBu(ONO)-W are mainly originated from the relaxation of the ILCT and LMCT states. • The luminescence mechanism is obtained by combining the theoretical method with the experimental results. [ABSTRACT FROM AUTHOR]

• Novel tungsten-containing organometallic complexes are synthesized. • Dual fluorescence emissions are originated from LL and LMCT excited states. • Femtosecond transient absorption is used to explain charge transfer in organometallic complexes. In this work, we first designed and synthesized two tungsten-containing organometallic complexes MeNOON and MeNOOO with novel dual fluorescence emissions. Moreover, the combined femtosecond ultrafast spectroscopy and time-dependent density functional theory (TDDFT) method has been performed to investigate the excited-state dynamics of MeNOON and MeNOOO complexes. It is distinctly demonstrated that dual fluorescence emissions of tungsten-containing organometallic complexes are originated from the localized-on-ligand (LL) and ligand-to-metal charge transfer (LMCT) excited states, respectively. Furthermore, the ultrafast LMCT process has been measured by the femtosecond spectroscopy. [ABSTRACT FROM AUTHOR]

In this work, the intermolecular hydrogen bonding interaction in both the ground state and electronic excited states of the hydrogen bonded compounds Serotonin–(H 2 O) n n = 1,2 were investigated by the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) method. By monitoring the structures in different electronic states, it has been demonstrated that the hydrogen bonds in Serotonin–(H 2 O) n n = 1, 2 are strengthened upon excitation. And the hydrogen bond site of 5-OH of the ring is always strengthened, more significantly. The simulated infrared (IR) spectrum demonstrated that the red-shifts of the stretching vibration frequencies of hydrogen bonded OH groups were consistent with the change trend of hydrogen bonds. Furthermore, the interaction among the hydrogen bonds caused by the bridged-water structure should be considered while making analysis of the calculated results such as the structure information and the IR spectrum. • TDDFT was performed to study the hydrated hydrogen bonding of Serotonin. • Hydrogen bonds in the electronic excited state were significantly strengthened. • Excited-state hydrogen bond strengthening was confirmed by vibrational spectra. • Photophysics of hydrated serotonin was affected by strengthened hydrogen bond. [ABSTRACT FROM AUTHOR]

In this work, we verified that the newly synthesized octyl urocanate compounds (U1 and U2) can significantly absorb UVB and confirmed their excellent light stability. In addition, we combined the Proton Nuclear Magnetic Resonance (1HNMR) and Time-Dependent Density Functional Theory (TDDFT) calculation methods to clearly explain the UV protection mechanism of U1 and U2. Octyl urocanate can be excited to an excited state after absorbing ultraviolet light in the UVB region. After that, the isomerized molecules at the conical intersection point (CI) between the potential energy surfaces (PESs) of the S 1 and S 0 states, rapidly relax to the ground state from the S 1 excited state in the form of a non-radiative transition. Ultrafast trans -cis photoisomerization can be carried out in a very short time. We found the characteristic peak of cis -U1 from the NMR of trans -U1 after being irradiated by the laser. Therefore, the energy absorbed by U1 and U2 can be quickly consumed through the non-radiative photoisomerization process. Therefore, we believe that octyl urocanate U1 and U2 are very good potential sunscreen molecules that absorb UVB. [Display omitted] • The compounds U1 and U2 with ultraviolet light were prepared by a new octyl urocanate. • U1 and U2 are obtained by esterification on the basis of natural product urocanic acid. • The absorb of U1 and U2 mainly is in the UVB region, and the fluorescence emission intensity is very small. • U1 and U2 can undergo cis -trans isomerization to relax energy after absorbing ultraviolet light. [ABSTRACT FROM AUTHOR]

In this work, the process of the Excited State Intramolecular Proton Transfer (ESIPT) competition of Kaempferol and Quercetin in methanol was studied by means of the Density Functional Theory (DFT) and the Time-Dependent Density Functional Theory (TDDFT) method. Two different ESIPT reaction pathways were analyzed by the variation trend of the 3D potential energy surfaces (PESs) with the change of the intramolecular hydroxyl bond length through the PESs of the two molecules of the ground state (S 0) and the first excited (S 1) state. The ESIPT process only occurred between O 25 –H 28 and O 22 –H 28 and was completed within 33.1fs by molecular excited state dynamics simulation. It is demonstrated that when there are two kinds of hydrogen bonds in the molecule, the ESIPT prefers the six-membered ring hydrogen bonds to the five-membered ring hydrogen bonds. [Display omitted] • The ESIPT competitive priority of adjacent hydrogen bonds has been studied. • A 3D potential energy surface was constructed to clarify the ESIPT process. • Excited state dynamics simulation verify the occurrence of ESIPT. • Kaempferol and Quercetin also have the potential to be used as sunscreens. [ABSTRACT FROM AUTHOR]