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[Display omitted] • New photoinduced decay mechanism of 3-OH-SMA system was proposed. • The decay channel is mainly driven by the C7 = N1 bond twisting motion. • The excited state intramolecular proton transfer process is not involved in 3-OH-SMA system. Schiff bases stand out as a highly significant class of photochromic materials with widespread applications. The exploration of their photochromic mechanisms has garnered substantial interest over the past decades. In this work, we investigated the photochromic mechanism of 3-hydroxy-salicylidene methylamine (3-OH-SMA) by high-level electronic structure calculations and on-the-fly excited state dynamics simulations. Our investigation revealed the identification of three minimum energy conical intersections between S 1 and S 0 states, while only the one characterized by the central C = N bond twisting motion was involved in the deactivation process. This finding contrasts with previous reports, suggesting that the excited state intramolecular proton transfer (ESIPT) process was the main reaction channel in 3-OH-SMA. The proposed new decay mechanism provides valuable theoretical insights, paving the way for the further enhancement or rational design of photochromic materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Methylation on the isomerizable alkene bond of plant sunscreen sinapates is first performed. • The critical role of molecular planarity breaking on accelerating this nonradiative process is highlighted. • This work provides a facile strategy to modulate the isomerization dynamics of photoswitches, proteins and sunscreens. E-Z photoisomerization constitutes the footstone of photosensitive proteins, molecular photoswitches and sunscreens and is believed to be controlled by photoinduced intramolecular charge transfer. In this work, we have made methylation on isomerizable alkene bond of plant sunscreen sinapate esters to break the coplanarity between phenol ring and C C double bond in ground state. Femtosecond transient absorption spectroscopy combined with time-dependent density functional theory calculations determine that this molecular planarity breaking triggers an immediate excited-state C C double bond twisting and thus accelerates the isomerization by more than one order of magnitude. These results highlight the role of molecular geometry on isomerization dynamics. [ABSTRACT FROM AUTHOR]

For computing the intra-chain excitonic couplings in polymeric systems, here we propose a new fragmentation approach. A comparison for the energetic and spatial properties of the low-lying excited states in PPV between our scheme and full quantum chemical calculations, reveals that our scheme can nicely reproduce full quantum chemical results in weakly coupled systems. Further wavefunction analysis indicate that improved description for strongly coupled system can be achieved by the inclusion of the higher excited states within each fragments. Our proposed scheme is helpful for building the bridge linking the phenomenological descriptions of excitons and microscopic modeling for realistic polymers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of BNBT with a high key-step yield based on simple raw materials. • An empirical linear relationship between Stokes shift and solvent parameters. • High fluorescence quantum yield and extremely low triplet yield of BNBT. We report a novel synthetic route of BN-benzo[b]triphenylene (BNBT) with a key-step yield exceeding 90% based on simple raw materials. The solvent effect on the optical absorption and fluorescence of BNBT is examined, and a linear relationship between the Stokes shift (Δ ν S) and the solvent parameters { α , β , π *} is generalized. The fluorescence lifetime correlates positively with the fluorescence quantum yield, which is about 10 folds of benzo[b]triphenylene (BT) as a structural counterpart (66% vs 6%). Moreover, the quantum yield of triplet-excited state BNBT is shown to be as low as a few thousandths. [ABSTRACT FROM AUTHOR]

[Display omitted] • The excited-state properties of three hydroxyanthraquinone compounds from the Marine Crinoid Pterometra venusta were studied by TDDFT. • After the excitation procession the pull shrinkage deformation about the middle ring is slightly stronger in HAQ3 than HAQ1 and HAQ2. • For S 0 → S 1 excitation, HAQ1 and HAQ2 is the local excitation of π-π*, while HAQ3 presents S 0 → S 1 as n-π*charge transfer excitation characteristic. Three natural hydroxyanthraquinone compounds HAQ (1–3) extracted from the Marine Crinoid Pterometra venusta. In order to identify their photochemical and electronic excited state properties of them, the theoretical research of optoelectronic properties have been studied. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, UV- absorbance and fluorescence emission spectra of HAQ (1–3) had been calculated. The results show that calculated spectra are very consistent with the experimental data. For S 0 → S 1 excitation, HAQ1 and HAQ2 are the local excitation of π-π*, while HAQ3 presents S 0 → S 1 as n-π*charge transfer excitation characteristic. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sensing mechanism of a fluorescence probe for fluoride and sulfite is theoretically confirmed. • Calculated VTEs are in good agreements with the UV–Vis and fluorescent spectra. • The probe-fluoride reaction product undergoes an ESPT process through hydrogen bonding. • ESPT process results in a red-shifted fluorescence of the probe. • Fluorescence of the probe is blue-shifted due to the inhibition of ICT process by sulfite. TDDFT method was applied to study the excited-state mechanism of a reported fluorescent probe for fluoride and sulfite. Theoretical results showed the excitation of the probe molecule involved an intramolecular charge transfer process. Based on potential energy scanning and frontier orbital analysis, the excited-state proton-transfer process of the fluoride-probe product resulted in the significant red-shifted fluorescence. In contrast, the intramolecular charge transfer process was inhibited by sulfite anions. Due to the curtailing of the conjugated system, a blue-shifted emission was observed in the fluorescence spectrum. By exploiting the difference in fluorescence wavelengths, fluoride and sulfite anions could be recognized. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of exchange–correlation functionals on charge-transfer excited states is tested. • The explicit solvent model gives a reasonable description of the electronic structure based on the QM/MM approach. • Red-shifts of the emission peak with increasing solvent polarity was reproduced in the theoretical calculations. ABSTRAC:A typical thermally activated delayed fluorescence (TADF) molecule, 3DPyM-pDTC was investigated theoretically in terms of geometric structure, absorption and emission spectra, and luminescence rates. The result of different XC functionals, the implicit and explicit solvent models on calculating geometries, and electron structures of the excited states were compared comprehensively. It's found that time-dependent density functional theory (TDDFT) with the PBE0 functional could give a rational description of the electron structure of 3DPyM-pDTC employing the explicit solvent model based on QM/MM. Red-shifts of the emission peak with increasing solvent polarity was reproduced. The TADF properties in the solid phase reproduced well. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photophysical properties of Azine derivative are discussed for TADF applications. • The position of excited state energy level are highlited from the TDDFT and DLPNO- STEOM-CCSD calculations. • Reason for the inverted singlet-triplet gap are explained on the basis of the high level calculations. TADF materials depend on the small energy gap between the lowest excited singlet and triplet state for an efficient reverse intersystem crossing process. Herein, the first excited singlet (S 1) and triplet (T 1) state and their gap (ΔE ST) are computed based on TDDFT and recently developed coupled-cluster DLPNO-STEOM-CCSD method for Azine derivative. Considerations of higher-order excitations in DLPNO-STEOM-CCSD assign the correct excited state energy level ordering of Azine derivative while DFT functionals fall short in this context. [ABSTRACT FROM AUTHOR]

Variations of the bond-path ellipticity ε profiles of the bond-path ( r ) of the torsional C2-C6 BCP corresponding to the (S 0 , S 1 , S 01) (left panel) (S 0 , S 2 , S 02) (right panel) electronic states at values of the torsion θ = 64.3° corresponding to the conical intersection (CI). The vertical dashed lines indicate the position of the BCP for each electronic state. • Present the S 0 → S 1 and S 0 → S 2 NTO densities for fulvene with 3-D next generation QTAIM. • Symmetrization of the S 0 → S 1 torsional BCP along bond-path found for the presence of a CI. • Corresponding NTO transition density S 0 → S 1 displays hindered BCP motion. • NTO density for S 0 → S 1 of the torsional BCP undergoes a large rearrangement at the CI. • Symmetrization effect absent for the S 0 → S 2 torsional BCP that lacks a CI. We present, for the first time, the S 0 → S 1 (S 01) and S 0 → S 2 (S 02) natural transition orbital (NTO) densities for fulvene, using the 3-D next generation QTAIM that can visualize and quantify the rearrangement of the charge density that occurs in response to the applied torsion and as a consequence of the preferred direction of electron density accumulation. A symmetrization of the position of the bond critical point (BCP) of the torsional C2-C6 BCP along the containing bond-path was determined to be characteristic of the presence of a conical intersection (CI) for the S 0 → S 1 (S 01) transition. [ABSTRACT FROM AUTHOR]

• Excited state chemistry of PRODAN derivative in methanol solvent was studied by TDDFT. • Intermolecular hydrogen bonds of PRODAN-3a-MeOH are enhanced in S 1 state. • For PRODAN-3a-MeOH, the S 1 state involves the intermolecular charge transfer. The role of intermolecular hydrogen bond of PRODAN derivative is investigated based on density functional theory (DFT) and time-dependent density functional theory (TDDFT). Geometry analysis demonstrated that the intermolecular hydrogen bonds are enhanced in S 1 state. The red-shift phenomenon of fluorescence spectrum and IR spectrum as well as the energy of intermolecular hydrogen bond further confirm the intermolecular hydrogen bond strengthening in excited state. PRODAN-3a-MeOH has been electronically excited to S 1 which is a local excitation. The small change of electron density occurred the interaction region of intermolecular can directly influence the intermolecular hydrogen bonding in S 1 state. [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]

• The sensing mechanism of a Schiff-base sensor has been theoretically confirmed. • Calculated excitation energies are in good agreements with reported spectra. • The TICT process could explain the weak fluorescence of the sensor. • S 0 and S 1 geometrical change are analyzed for the sensor and its anion. The fluoride-sensing mechanism of a Schiff-base type sensor (Dyes Pigments, 2015, 123, 166) has been investigated by time-dependent density functional theory. The experimental ultraviolet and fluorescence spectra of the sensor before and after fluoride addition were well reproduced. The theoretical results showed that sensor molecules had distinctly different geometries in the ground state and first singlet excited state, which corresponded with the proposed twisted intramolecular charge transfer process and explained how the sensor fluorescence quenched. Thus, the sensor analysis of the fluoride anion by fluorescent spectroscopy was explained. [ABSTRACT FROM AUTHOR]