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The photophysical properties of a series of recently synthesized single benzene fluorophores were investigated using ensemble density functional theory calculations. The energetic stability of the ground and excited state species were counterposed against the aromaticity index derived from local vibrational modes. It was found that the large Stokes shift of the fluorophores (up to ca. 5800 cm −1) originates from the effect of electron donating and electron withdrawing substituents rather than π‐delocalization and related (anti‐)aromaticity. On the basis of nonadiabatic molecular dynamics simulations, the absence of fluorescence from one of the regioisomers was explained by the occurrence of easily accessible S 1/S 0 conical intersections below the vertical excitation energy level. It is demonstrated in the manuscript that the analysis of local mode force constants and the related aromaticity index represent a useful tool for the characterization of π‐delocalization effects in π‐conjugated compounds. [ABSTRACT FROM AUTHOR]

The dynamics of excited‐state charge transfer (CT) in second near‐infrared (NIR‐II) fluorophore proceeds with conformational change that govern fluorescence. Unveiling the relationship between CT dynamics and conformational change in excited state is of great fundamental significance in optimizing NIR‐II fluorescence but remains less explored. This study unveils the pivotal role of large conformational change in promoting the evolution of emissive CT state into nonemissive CT state in NIR‐II fluorophore (CA‐BBT). Spectroscopic and computational results reveal that large conformational rotation/twisting leads to a pronounced increase in the CT character in excited state. This heightened CT character in CA‐BBT enables a rapid evolution of emissive CT state into a nonemissive CT state within 1.4 ps, as observed by ultrafast spectroscopy. Subsequently, this nonemissive state dominates nonradiative decay, resulting in very low NIR‐II fluorescence. Preventing such detrimental evolution by constraining the conformational dynamics of CA‐BBT results in a 10‐fold enhancement of NIR‐II fluorescence, enabling high‐resolution dynamic visualization of vasculature within osteosarcoma. This study offers a profound understanding of the relationship between CT dynamics and conformational changes in NIR‐II fluorescence, presenting innovative perspectives to develop bright NIR‐II fluorophores. [ABSTRACT FROM AUTHOR]

In this research, the ground (µg) and excited (µe) state dipole moments of metformin hydrochlorides were determined using Lippert-Mataga, Bakhshiev's, Kawski-Chamma-Viallet, and Reichardt models from fluorescence emission and UV-Vis absorption spectra in various solvents. From solvatochromic effects the calculated excited (µe) dipole moment of metformin hydrochloride were, 8.55 D, 8.34 D, 6.08 D, and 6.40 D using the Lippert-Mataga, Bakhshiev's, Kawski-Chamma-Viallet and Reichardt models respectively. The results also indicated that the dipole moment at the ground state is smaller than the excited state. This is due to solvent polarity having a stronger effect on fluorescence emission than absorption spectra. Similarly, from density functional theory, the calculated ground and excited states dipole moments of metformin hydrochloride using (DFT-B3LYP- 3-21+G*(μg = 10.02 D and μe = 11.94 D), DFT-B3LYP- 6-31+G (d, p) (μg = 8.44 D and μe = 10.87 D), and DFT-B3LYP- 6-311+G (d, p) (μg = 8.24 D and μe = 18.74 D)) analyzed by Gaussian 09W. From the optimized geometry of the molecule, the HOMO-LUMO energy band gap of metformin hydrochloride were computed using DFT [DFT-B3LYP- 3-21+G*(5.51 eV), DFT-B3LYP- 6-31+G (d, p) (5.66 eV), and DFT-B3LYP- 6-311+G (d, p) (5.70 eV)] respectively. [ABSTRACT FROM AUTHOR]

Recent advances in synthetic methods, combined with tip‐induced on‐surface chemistry, have enabled the formation of numerous cyclocarbon molecules. Here, we investigate computationally the experimentally studied C16 and C18 molecules as well as their van der Waals (vdW) complexes with several typical donor and acceptor molecules. Our results demonstrate a remarkable electron‐withdrawing ability of cyclocarbon molecules. The vdW complexes of C16 and C18 exhibit a thermodynamically favorable photoinduced electron transfer (ET) from the donor partner to the cyclocarbons that occurs on a picosecond time scale. The lower reorganization energy of C16 compared to C18 leads to a significant acceleration of the ET reactions. [ABSTRACT FROM AUTHOR]

Time‐dependent density functional theory (TD‐DFT) and multiconfigurational second‐order perturbation theory (CASPT2) are two of the most widely used methods to investigate photoinduced dynamics in DNA‐based systems. These methods sometimes give diverse dynamics in physiological environments usually modeled by quantum mechanics/molecular mechanics (QM/MM) protocol. In this work, we demonstrate for the uridine test case that the underlying topology of the potential energy surfaces of electronic states involved in photoinduced relaxation is similar in both electronic structure methods. This is verified by analyzing surface‐hopping dynamics performed at the QM/MM level on aqueous solvated uridine at TD‐DFT and CASPT2 levels. By constraining the dynamics to remain on ππ* state we observe similar fluctuations in energy and relaxation lifetimes in surface‐hopping dynamics in both TD‐DFT and experimentally validated CASPT2 methods. This finding calls for a systematic comparison of the ES potential energy surfaces of DNA and RNA nucleosides at the single‐ and multi‐reference levels of theory. The anomalous long excited state lifetime at the TD‐DFT level is explained by nπ* trapping due to the tendency of TD‐DFT in QM/MM schemes with electrostatic embedding to underestimate the energy of the ππ* state leading to a wrong ππ*/nπ* energetic order. A study of the FC energetics suggests that improving the description of the surrounding environment through polarizable embedding or by the expansion of QM layer with hydrogen‐bonded waters helps restore the correct state order at TD‐DFT level. Thus by combining TDDFT with an accurate modeling of the environment, TD‐DFT is positioned as the standout protocol to model photoinduced dynamics in DNA‐based aggregates and multimers. [ABSTRACT FROM AUTHOR]

In organisms, amino acids usually use water as a solvent which is an important component for cell formation. In this environment, the formation of intermolecular hydrogen bonds will affect the structure and properties of amino acids and water molecules. In order to study its properties in the ground state and excited state, in this paper, we use density functional theory（DFT) and time-dependent density functional theory（TD-DFT) to analyze the electrostatic potential, bond length, natural bond orbital（NBO) charge, Atoms In Molecules（AIM), Wiberg bond order b, infrared（IR) spectroscopy, hole-electron orbits of intermolecular hydrogen bonds between glycine and H2O in the ground and excited states, the hole electron orbit and the electron transfer between ground state and excited state are studied theoretically. The results show that the intermolecular hydrogen bond formation will lead to the change of molecular structure and the shift of infrared spectral vibration frequency. In the excited states, the intermolecular hydrogen bond is strengthened or weakened to different degrees. The results provide a theoretical basis for forming hydrogen bonds and the study of intermolecular hydrogen bonds in excited states. [ABSTRACT FROM AUTHOR]

The dynamics of excited‐state charge transfer (CT) in second near‐infrared (NIR‐II) fluorophore proceeds with conformational change that govern fluorescence. Unveiling the relationship between CT dynamics and conformational change in excited state is of great fundamental significance in optimizing NIR‐II fluorescence but remains less explored. This study unveils the pivotal role of large conformational change in promoting the evolution of emissive CT state into nonemissive CT state in NIR‐II fluorophore (CA‐BBT). Spectroscopic and computational results reveal that large conformational rotation/twisting leads to a pronounced increase in the CT character in excited state. This heightened CT character in CA‐BBT enables a rapid evolution of emissive CT state into a nonemissive CT state within 1.4 ps, as observed by ultrafast spectroscopy. Subsequently, this nonemissive state dominates nonradiative decay, resulting in very low NIR‐II fluorescence. Preventing such detrimental evolution by constraining the conformational dynamics of CA‐BBT results in a 10‐fold enhancement of NIR‐II fluorescence, enabling high‐resolution dynamic visualization of vasculature within osteosarcoma. This study offers a profound understanding of the relationship between CT dynamics and conformational changes in NIR‐II fluorescence, presenting innovative perspectives to develop bright NIR‐II fluorophores.

Photocatalytic CO2 reduction is one of the best solutions to solve the global energy crisis and to realize carbon neutralization. The tetradentate phosphine‐bipyridine (bpy)‐phosphine (PNNP)‐type Ir(III) photocatalyst, Mes‐IrPCY2, was reported with a high HCOOH selectivity but the photocatalytic mechanism remains elusive. Herein, we employ electronic structure methods in combination with radiative, nonradiative, and electron transfer rate calculations, to explore the entire photocatalytic cycle to either HCOOH or CO, based on which a new mechanistic scenario is proposed. The catalytic reduction reaction starts from the generation of the precursor metal‐to‐ligand charge transfer (3MLCT) state. Subsequently, the divergence happens from the 3MLCT state, the single electron transfer (SET) and deprotonation process lead to the formation of one‐electron‐reduced species and Ir(I) species, which initiate the reduction reaction to HCOOH and CO, respectively. Interestingly, the efficient occurrence of proton or electron transfer reduces barriers of critical steps. In addition, nonadiabatic transitions play a nonnegligible role in the cycle. We suggest a lower free‐energy barrier in the reaction‐limiting step and the very efficient SET in 3MLCT are cooperatively responsible for a high HCOOH selectivity. The gained mechanistic insights could help chemists to understand, regulate, and design photocatalytic CO2 reduction reaction of similar function‐integrated molecular photocatalyst. [ABSTRACT FROM AUTHOR]

Aryl‐maleimides undergo a novel [2+4]‐photodimerization instead of the expected [2+2]‐photodimerization under both direct irradiation with visible light and under sensitized energy transfer conditions. This new excited state reactivity in aryl‐maleimides is deciphered through photochemical, photophysical, and spectroscopic studies. The stereochemistry of the photodimer depends on the type of non‐bonding interactions prevalent during photodimerization which is in turn dictated by the substituents on the maleimide ring. More importantly, the stereochemistry of the photodimer formed is complementary to the product observed under thermal conditions. [ABSTRACT FROM AUTHOR]

A series of reported Pt(II) carbene complexes possibly have the ability to serve as the new generation of blue emitters in luminescent devices because of their narrow emission spectra, high photoluminescence quantum yields (PLQYs), and rigid molecular skeleton. However, the combination of all carbene ligands with different multidentate structures will affect the overall planarity and horizontal dipole ratio to varying degrees, but the specific extent of this effect has not previously been analyzed in detail. In this work, density functional computation is used to study a class of platinum tetracarbene bidentate complexes with similar absorption and emission band characteristics, which is the main reason for the remarkable difference in quantum efficiency due to subtle differences in electronic states caused by different ligands. From the calculation results, the major reason, which results in significantly decrease in quantum efficiency for [Pt(cyim)2]2+, is that [Pt(cyim)2]2+ can reach the non-radiative deactivation metal-centered d-d excited state through an easier pathway compared with [Pt(meim)2]2+. The result, based on changes in the dihedral angle between ligands, can achieve the goal of improving and designing materials by adjusting the degree of the dihedral angle. (meim: bis(1,1′-dimethyl-3,3′-methylene-diimidazoline-2,2′-diylidene); cyim: bis(1,1′-dicyclohexyl-3,3′-methylene-diimidazoline-2,2′-diylidene). [ABSTRACT FROM AUTHOR]

Cluster B12C4N8 has a broad application prospect. It is of great significance for investigating the properties of cluster B12C4N8 under the external electric field. The dipole moment, energy gap and infrared spectrum of cluster B12C4N8 molecule under external electric field (0–30 V/nm) are studied with density functional theory at B3LYP/6-31G(d) level. The dipole moment increases almost linearly from 0.87838 to 30.79096 Debye and the energy gap decreases continuously. Meanwhile, the ultraviolet-visible absorption spectra, the excitation wavelength, the excitation energy, oscillator strength and real space representation of hole and electron distributions of first ten excited states of cluster B12C4N8 under the external electric field are also studied with the time-dependent density functional theory at B3LYP/6-31G(d) level. It is found that the absorption peak of cluster B12C4N8 occurs blue shift. The excitation energy decreases significantly as the external electric field increases from 0 to 15 V/nm, increases as the external electric field increases from 15 to 20 V/nm, and decreases almost linearly as the external electric field increases from 20 to 30 V/nm. The results can offer an important reference to use external electric Fifield to tune the properties of cluster B12C4N8. [ABSTRACT FROM AUTHOR]

spectral dependencies of the electroluminescence intensity of a microdisk laser with a diameter of 31 μm with active region based on InAs/InGaAs quantum dots, operating in the continuous-wave regime, are investigated in a wide range of injection currents. Simultaneous lasing through the ground and excited states of quantum dots under intense excitation is demonstrated in injection microdisk laser for the first time. At low pumping powers lasing occurs via ground states of quantum dots only. [ABSTRACT FROM AUTHOR]

We here disclose that the incorporation of thiophene rings into a seven‐membered 8π azepine in a fused fashion produces a useful antiaromatic core for near‐infrared (NIR) dyes. In contrast to dibenzazepine derivatives with bent structures, dithieno‐fused derivatives with electron‐accepting groups adopt flat conformations in the ground state. The dithieno‐fused derivatives exhibited broad absorption spectra that cover the visible region as well as sharp emission bands in the NIR region, which are considerably red‐shifted relative to those of the dibenzo‐fused congeners. Theoretical study revealed two contradictory effects of the less‐aromatic thiophene‐fused structure, i.e. the enhancement of the antiaromaticity of the adjacent azepine ring and the relief of the antiaromaticity through the contribution of a quinoidal resonance form. The combination of the dithienoazepine core with cationic electron‐accepting groups produced a NIR fluorescent dye with an emission at 878 nm in solution. [ABSTRACT FROM AUTHOR]

The rationality of the minimum electrophilicity principle (MElP) as a companion of minimum polarizability principle and maximum hardness principle is studied for simple diatomic, triatomic, and tetratomic molecules. The applicability is further justified considering organic molecules (e.g., pyrene and acridine yellow) are known for their photophysical properties and accordingly their excited state properties. Single excitation CI (CIS) and time‐dependent density functional theory (TDDFT) are employed to study the excited state reactivity. Two types of excitations, namely vertical and adiabatic, are considered. Processes involving conservation and change in spin multiplicity are included during excitation. The general trend is that the molecules are less electrophilic in the ground state than those in the corresponding excited states. It is found that adiabatic excitation validates the principle even for the triplet ground state molecules undergoing an excitation where spin multiplicity gets altered. The TDDFT method explains the validity of the MElP augmenting the CIS method. This study echoed the MElP during molecular electronic excitation. [ABSTRACT FROM AUTHOR]

Using a new approach to the problem of calculating the total energy of a diatomic molecule in terms of the first-order perturbation theory, it was shown that the potential energy screening function is a solution to a diffusion-type equation in which the role of a time variable is played by the mean square of the amplitude of collective vibrations of electrons per one degree of freedom. The total energy of two carbon atoms in the ground and excited states was calculated. [ABSTRACT FROM AUTHOR]

A photochemical synthetic method to access sulfones from aryl halides and sodium alkylsulfinates in the presence of CuCl is reported. Regio‐ and chemoselectivity for the sulfonylation is observed for polyhalogenated arenes. Mechanistic studies indicate that a copper sulfinate reagent is formed in situ from CuCl and sodium sulfinate based on NMR experiments. Potential reaction intermediates, including excited state aryl halides are studied using density functional theory calculations and reveal energetically accessible non‐planar triplet geometries. [ABSTRACT FROM AUTHOR]

Disulfide bonds are critical structural elements in proteins and stabilize folded structures. Modification of these linkages is associated with a loss of structure and function. Previous studies have reported large variations in the rate of disulfide oxidation by hypohalous acids, due to stabilization of reaction intermediates. In this study we hypothesized that considerable variation (and hence selective oxidation) would occur with singlet oxygen (1O 2), a key intermediate in photo-oxidation reactions. The kinetics of disulfide-mediated 1O 2 removal were monitored using the time-resolved 1270 nm phosphorescence of 1O 2. Stern-Volmer plots of these data showed a large variation (∼103) in the quenching rate constants k q (from 2 × 107 for α-lipoic acid to 3.6 × 104 M−1s−1 for cystamine). The time course of disulfide loss and product formation (determined by LC-MS) support a role for 1O 2 , with mono- and di-oxygenated products detected. Elevated levels of these latter species were generated in D 2 O- compared to H 2 O buffers, which is consistent with solvent effects on the 1O 2 lifetime. These data are interpreted in terms of the intermediacy of a zwitterion [–S+(OO−)–S–], which either isomerizes to a thiosulfonate [–S(O) 2 –S–] or reacts with another parent molecule to give two thiosulfinates [–S(O)–S-]. The variation in quenching rates and product formation are ascribed to zwitterion stabilization by neighboring, or remote, lone pairs of electrons. These data suggest that some disulfides, including some present within or attached to proteins (e.g., α-lipoic acid), may be selectively modified, and undergo subsequent cleavage, with adverse effects on protein structure and function. [Display omitted] • Kinetics of disulfide-mediated 1O 2 removal monitored using time-resolved phosphorescence. • Rate constants for 1O 2 removal show a marked variation with structure (103 -107 M−1 s−1). • 5-membered ring disulfides (lipoic acid, lipoamide) react more rapid than linear disulfides. • LC-MS analyses show formation of mono- (thiosulfinate) and di-oxygenated (thiosulfonate) products. • Protein disulfides may show similar variable reactivity and selective oxidation. [ABSTRACT FROM AUTHOR]

Celecoxib is a highly selective inhibitor of COX-2. After 20 years of development, it has become the most widely used prescription drug in the world. This paper is based on density functional theory and uses B3LYP functional, 6-311++G (d,p) basis set for structural optimization. In this work, a series of studies have been done on the structure, infrared spectrum, Raman spectrum, molecular frontier orbital, electrostatic potential and excited state properties of the drug molecule. The results show that CXB molecule is a stable non-planar twisted structure, which allows the drug molecule to quickly pass through the hydrophobic channel on COX-2, thereby forming a binding cavity that can bind to the benzene-sulfonamide fragment. The frequency of the compound is calculated, the infrared spectrum and Raman spectrum are obtained respectively, which are compared with the data collected by the experiment, showing a high degree of consistency. The frontier orbital and electrostatic potential were analyzed for the ground state of the molecule, and the sulfonamide group and COX-2 were easy to form hydrogen bonds. In the study of the excited state of CXB molecule, it is found that the excited state property of CXB molecule is mainly determined by the first excited state, the third excited state and the sixth excited state. This provides important information for understanding the mechanism of action of CXB, and also provides a theoretical basis for later expansion of CXB derivatives. [ABSTRACT FROM AUTHOR]

Photo-controlled self-assembly of nanoparticles (NPs) is an advanced and promising approach to address a series of material issues from the molecular level to the nano/micro scale, owing to the fact that light stimulus is typically precise and rapid, and can provide contactless spatial and temporal control. The traditional photo-controlled assembly of NPs is based on photochemical processes through NPs modified by photo-responsive molecules, which are realized through the change in chemical structure under irradiation. Moreover, photoexcitation-induced assembly of NPs is another promising physical strategy, and such a strategy aims to employ molecular conformational change in the excited state (rather than the chemical structure) to drive molecular motion and assembly. The exploration and control of NP assembly through such a photo-controlled strategy can open a new paradigm for scientists to deal with "bottom-up" behaviors and develop unprecedented optoelectronic functional materials. [ABSTRACT FROM AUTHOR]

Photoionization of neutral chlorine atom is investigated in this paper in the framework of the screening constant per unit nuclear charge (SCUNC) method. Resonance energies, quantum defects and effective charges of the 3s23p4 (3P2,1,0)ns and 3s23p4 (3P1,0)nd Rydberg series originating from both the 2P03/2 ground state and the 2P01/2 excited state of chlorine atom are reported. The present study believed to be the first theoretical investigation is compared with the recent experimental measurements (Yang et al., Astrophys. J. 810:132, 2015). Good agreements are obtained between theory and experiments. New SCUNC data are tabulated as useful references for interpreting astrophysical spectra from neutral atomic chlorine. [ABSTRACT FROM AUTHOR]

A series of reported Pt(II) carbene complexes possibly have the ability to serve as the new generation of blue emitters in luminescent devices because of their narrow emission spectra, high photoluminescence quantum yields (PLQYs), and rigid molecular skeleton. However, the combination of all carbene ligands with different multidentate structures will affect the overall planarity and horizontal dipole ratio to varying degrees, but the specific extent of this effect has not previously been analyzed in detail. In this work, density functional computation is used to study a class of platinum tetracarbene bidentate complexes with similar absorption and emission band characteristics, which is the main reason for the remarkable difference in quantum efficiency due to subtle differences in electronic states caused by different ligands. From the calculation results, the major reason, which results in significantly decrease in quantum efficiency for [Pt(cyim)2]2+, is that [Pt(cyim)2]2+ can reach the non-radiative deactivation metal-centered d-d excited state through an easier pathway compared with [Pt(meim)2]2+. The result, based on changes in the dihedral angle between ligands, can achieve the goal of improving and designing materials by adjusting the degree of the dihedral angle. (meim: bis(1,1′-dimethyl-3,3′-methylene-diimidazoline-2,2′-diylidene); cyim: bis(1,1′-dicyclohexyl-3,3′-methylene-diimidazoline-2,2′-diylidene).

The photo‐responsive adsorption has emerged as a vibrant area, but its current methodology is limited by the well‐defined photochromic units and their molecular deformation driven by photo‐stimuli. Herein, a methodology of nondeforming photo‐responsiveness is successfully exploited. With the exploiting agent of Cu‐TCPP framework assembled on the graphite and strongly interacted with it, the sorbent generates two kinds of adsorption sites, over which the electron density distribution of the graphite layer can be modulated at the c‐axis direction, which can further evolve due to photo‐stimulated excited states. The excited states are stable enough to meet the timescale of microscopic adsorption equilibrium. Independent of the ultra‐low specific surface area of the sorbent (20 m2 g−1), the CO adsorption capability can be improved from 0.50 mmol g−1 at the ground state to 1.24 mmol g−1 (0 °C, 1 bar) with the visible light radiation, rather than the photothermal desorption. [ABSTRACT FROM AUTHOR]

Donor–π–acceptor fluorophores that consist of an electron‐donating amino group and an electron‐accepting triarylborane moiety generally exhibit substantial solvatochromism in their fluorescence while retaining high fluorescence quantum yields even in polar media. Herein, we report a new family of this compound class, which bears ortho‐P(=X)R2‐substituted phenyl groups (X=O or S) as a photodissociative module. The P=X moiety that intramolecularly coordinates to the boron atom undergoes dissociation in the excited state, giving rise to dual emission from the corresponding tetra‐ and tricoordinate boron species. The susceptibility of the systems to photodissociation depends on the coordination ability of the P=O and P=S moieties, whereby the latter facilitates dissociation. The intensity ratios of the dual emission bands are sensitive to environmental parameters, including temperature, solution polarity, and the viscosity of the medium. Moreover, precise tuning of the P(=X)R2 group and the electron‐donating amino moiety led to single‐molecule white emission in solution. [ABSTRACT FROM AUTHOR]

Intramolecular charge transfer and the associated changes in molecular structure in N,N'-dimethylpiperazine are tracked using femtosecond gas-phase X-ray scattering. The molecules are optically excited to the 3p state at 200 nm. Following rapid relaxation to the 3s state, distinct charge-localized and charge-delocalized species related by charge transfer are observed. The experiment determines the molecular structure of the two species, with the redistribution of electron density accounted for by a scattering correction factor. The initially dominant charge-localized state has a weakened carbon-carbon bond and reorients one methyl group compared with the ground state. Subsequent charge transfer to the charge-delocalized state elongates the carbon-carbon bond further, creating an extended 1.634 Å bond, and also reorients the second methyl group. At the same time, the bond lengths between the nitrogen and the ring-carbon atoms contract from an average of 1.505 to 1.465 Å. The experiment determines the overall charge transfer time constant for approaching the equilibrium between charge-localized and charge-delocalized species to 3.0 ps.

Abstract The temperature-dependent dual fluorescence from a single component of small organic molecules (SOMs) is very promising for the ratiometric fluorescence sensing of temperature. However, the SOM-based fluorophores typically only show one fluorescence band. It is thus very challenging to achieve dual fluorescence, let alone the dual fluorescence that is sensitive to temperature. Herein, in this short review, we briefly summarized the examples of SOM-based fluorophores exhibiting temperature-dependent dual fluorescence. Through representative examples, we mainly focus on the illustration of the intrinsic mechanisms of this unusual phenomenon, which may take place because of the presence of two local minimum conformations that are thermally equilibrated in the ground state, the presence of two local minimum conformations in the first excited state as the result of significant structural relaxation upon excitation, or the presence of thermal equilibrium between the first and second excited states. Hopefully, the discussions in this short review will provide some important guidelines for the further rational molecular design of such fluorophores.

Helicenes are an interesting scaffold for chiroptical properties and in particular circularly polarized luminescence (CPL). In this short review, we collect the luminescence (glum) and absorption (gabs) dissymmetry factors associated to the first Cotton effect of the electronic circular dichroism (ECD) spectrum. Considering the data for 170 [n]‐helicenes (n = 4–11), overall we found reasonable correlations between glum and gabs. Despite a few notable exceptions, this would confirm a similarity in the stereochemistry of the ground and emitting excited states for most helicenes. These results may be useful in rationalizing chiroptical data and help chemists in designing new helicene structures with the desired CPL properties. [ABSTRACT FROM AUTHOR]

Pressure‐induced emission (PIE) associated with self‐trapping excitons (STEs) in low‐dimensional halide perovskites has attracted great attention for better materials‐by‐design. Here, using 2D layered double perovskite (C6H5CH2CH2NH3+)4AgBiBr8 as a model system, we advance a fundamental physicochemical mechanism of the PIE from the perspective of carrier dynamics and excited‐state behaviors of local lattice distortion. We observed a pressure‐driven STE transformation from dark to bright states, corresponding a strong broadband Stokes‐shifted emission. Further theoretical analysis demonstrated that the suppressed lattice distortion and enhanced electronic dimensionality in the excited‐state play an important role in the formation of stabilized bright STEs, which could manipulate the self‐trapping energy and lattice deformation energy to form an energy barrier between the potential energy curves of ground‐ and excited‐state, and enhance the electron‐hole orbital overlap, respectively. [ABSTRACT FROM AUTHOR]

The theoretical investigation of excited state for large photoactive systems plays the fundamental role in understanding various optical processes in material and biological system. Frenkel exciton (FE) model describing the excitation of the whole system as a collective effect of quasi‐particles of excitons, that is, bound electron–hole pairs, is well‐known as a simple but powerful theoretical scheme to present a clear and insightful physical picture for complicated excited state problems. In this mini‐review, we summarize our recent developments of quantum chemical methods based on exciton models and their related applications for large photoactive systems. It is shown that our developed ab initio renormalized exciton model (REM) and block interaction product state (BIPS) schemes provide new efficient and automatic low‐scaling excited state methods for both localized and delocalized excited states in large systems. Illustrative examples including simulations of both absorption and emission spectrum in large sized molecular aggregates, indicate the exciton model based methods provide promising computational tools for unravel the mechanism of photophysical and photochemical processes in large photoactive systems. [ABSTRACT FROM AUTHOR]

It is shown that, like conventional diffuse fluorescence spectra and despite the complex mechanism of formation of the excited state, the chemi- and bioluminescence spectra contain information about the frequency of the purely electronic (vertical) transition of the emitting molecules and the degree of homogeneity of their ensemble. As in the case of ordinary diffuse luminescence spectra, the frequency of a purely electronic transition is shifted significantly toward the short wavelength side (by almost the half-width of the band) from the maximum of the fluorescence spectrum. An example of the separation of the overlapping spectra using the position of a short-wavelength purely electronic transition is presented. [ABSTRACT FROM AUTHOR]

Photo-controlled self-assembly of nanoparticles (NPs) is an advanced and promising approach to address a series of material issues from the molecular level to the nano/micro scale, owing to the fact that light stimulus is typically precise and rapid, and can provide contactless spatial and temporal control. The traditional photo-controlled assembly of NPs is based on photochemical processes through NPs modified by photo-responsive molecules, which are realized through the change in chemical structure under irradiation. Moreover, photoexcitation-induced assembly of NPs is another promising physical strategy, and such a strategy aims to employ molecular conformational change in the excited state (rather than the chemical structure) to drive molecular motion and assembly. The exploration and control of NP assembly through such a photo-controlled strategy can open a new paradigm for scientists to deal with “bottom-up” behaviors and develop unprecedented optoelectronic functional materials.

With the deterioration of global greenhouse effect, CF3SO2F (Trifluoromethanesulphonyl Fluoride) has become an alternative gas of SF6 (Sulfur Hexafluoride). CF3SO2F has environmentally friendly characteristics and has been widely concerned. In this work, we analyze the electric field level of the discharge in the dielectric and the direction of the molecular intrinsic dipole moment. Density functional theory and time-dependent density functional theory are used to calculate the molecular structure parameters, dipole moments, frontier orbitals and excited states at corresponding electric field levels and in specific electric field directions. C2F5SO2F and C3F7SO2F, as by-products in the synthesis of CF3SO2F, are studied together to explore the influence of carbon atom number on molecular properties. As a result, the molecular structure is clearly changed under the electric field and the molecular bond length strongly depended on the electric field. The HOMO is mainly contributed by O atoms and the LUMO is mainly contributed by S atoms. When the electric field in the -z-axis direction is applied, the HOMO energies of molecules increase, especially for C3F7SO2F molecule, and the ionization potentials decrease correspondingly. The reduced ionization potentials facilitate the liberation of electrons from the molecule and the propagation of the streamer. The excitation energy of each molecule in each excited state decreases with the increasing of electric field intensity. Therefore, during the preparation process of CF3SO2F molecule, C3F7SO2F molecule should be reduced or removed as much as possible to prevent the reduction of dielectric insulation strength. The finding of this study is beneficial to the performance improvement and application research of CF3SO2F.

The search for new materials is constantly ongoing. Recently, a two-dimensional carbon allotrope , γ-graphyne, has been synthesized with a unified crystalline structure . Because of its low LUMO and excellent electron mobility, it appears to be a promising electron acceptor for photovoltaic applications. Here we report an analysis of the electronic properties of model van der Waals complexes of γ-graphyne with several partners of different electronic nature. We show that photoinduced electron transfer from electron-donating partners to γ-graphyne is favorable and occurs on nano to picosecond time scale. In contrast, electron transfer from γ-graphyne to strong electron acceptors is unlikely. Our results open perspectives for the future application of γ-graphyne in photovoltaic devices.

The impact of the connection modes between donor (D) and acceptor (A) on the luminescence properties is revealed for organic D‐A‐D emitters based on triphenylamine (TPA) and 9,10‐phenanthroquinone (PAQ). When TPA and PAQ are linked via a single bond, the emitters exhibit small energy difference between the lowest singlet and triplet excited states (∆EST) due to the separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions, thus featuring thermally activated delayed fluorescence (TADF). Interestingly, for the emitters with TPA and PAQ sharing a benzene ring, the ∆EST are significantly increased because of the enhanced overlap between the HOMO and LUMO, which is beneficial to realize room temperature phosphorescence (RTP). Moreover, upon changing the connection from β to γ‐position, high‐lying triplet states can become energetically lower than the lowest singlet excited state, thus affording additional channels to facilitate TADF and RTP. This work sheds some light on controlling of the excited state energy level alignments via modulating the D‐A connection modes to tune molecular emission from TADF to RTP. [ABSTRACT FROM AUTHOR]

In this review, we have attempted to briefly summarize the influence of an external electric field on an assembly of tautomeric molecules and to what experimentally observable effects this interaction can lead to. We have focused more extensively on the influence of an oriented external electric field (OEEF) on excited-state intramolecular proton transfer (ESIPT) from the studies available to date. The possibilities provided by OEEF for regulating several processes and studying physicochemical processes in tautomers have turned this direction into an attractive area of research due to its numerous applications. [ABSTRACT FROM AUTHOR]

Visible light photocatalysis has established itself as a promising sustainable and powerful strategy to access reactive intermediates, i.e. radicals and radical ions, under mild reaction conditions using visible light irradiation. This field enables the development of formerly challenging or even previously inaccessible organic transformations. In this tutorial review, an overview of the essential concepts and techniques of visible-light-mediated chemical processes and the most common types of photochemical activation of organic molecules, i.e. photoredox catalysis and photosensitization, are discussed. Selected photocatalytic alkene functionalization reactions are included as examples to illustrate the basic concepts and techniques with particular attention given to the understanding of their reaction mechanisms. 1 Introduction 2 Photocatalysts 3 Photophysical and Electrochemical Properties 3.1 Excited-State Energy 3.2 Ground-State Redox Potentials 3.3 Excited-State Redox Potentials 3.4 Local Absorbance Maximum for Lowest Energy Absorption 3.5 Excited-State Lifetime 3.6 [Ru(bpy)3 ]2+ as a Case Study 3.7 Basic Laws and Equations of Photochemistry and Photocatalysis 3.8 Common Terminology in Photochemistry and Photocatalysis 4 Activation Modes in Photocatalysis 4.1 Photoinduced Electron Transfer 4.2 Photoinduced Energy Transfer 5 Conclusions and Outlook [ABSTRACT FROM AUTHOR]

Here, photovoltaic behaviors of the human-shaped molecules named NanoKid and NanoAthlete (monomeric forms) and NanoPutain dimer1 and NanoPutain dimer2 (hetero-dimers) based on the quantum chemistry were investigated. For all studied anthropomorphic molecules, tuning the electrophilicity decreases the energy barrier of the electron injection. NanoKid and NanoAthlete have greater activity against solar light, which show more favorable photovoltaic parameters. Although NanoPutain dimers represent better charge transfer indices and intramolecular charge transfer, they have low oscillating strength. The maximum peaks of the current in different absorption wavelengths are originated from the increase in the light-harvesting efficiency and decrease in the energy barrier of the electron injection. Finally, NanoKid and NanoAthlete are proposed as better candidates to be used in the photovoltaic cells. [ABSTRACT FROM AUTHOR]

Ultrafast optical spectroscopy delivers unparalleled insights into the dynamic response of photoactive materials, including semiconducting, photonic and phase-change materials. The most applied experimental tool – transient absorption spectroscopy – derives signals from induced changes in the intensity of transmitted light, assumed to relate to the imaginary part of the refractive index. However, the entire complex refractive index of materials changes in the excited state; changes in the real part of the refractive index can have significant effects on transient absorption spectra and the function of optical devices. In this review, we introduce an emerging ultrafast spectroscopy method – frequency domain interferometry. This simple adaptation of transient absorption spectroscopy provides a model-independent means of spectrally resolving photoinduced changes in a materials refractive index. After introducing the theory and implementation of the method, we describe several case studies, including the optical response of metal-halide perovskites and phase modulators, and surface displacement of phase-change materials. Finally, we describe recent and future improvements that can enhance the time-resolution and signal sensitivity of this technique. The advances and applications highlighted in this review demonstrate the potential of the method to become a standard part of the ultrafast spectroscopy toolbox for characterising optoelectronic and photonic materials and devices.

Ultraviolet photodissociation or UVPD is an increasingly popular option for tandem-mass spectrometry experiments. UVPD can be carried out at many wavelengths, and it is important to understand how the results will be impacted by this choice. Here, we explore the utility of 213 nm photons for initiating bond-selective fragmentation. It is found that bonds previously determined to be labile at 266 nm, including carbon-iodine and sulfur-sulfur bonds, can also be cleaved with high selectivity at 213 nm. In addition, many carbon-sulfur bonds that are not subject to direct dissociation at 266 nm can be selectively fragmented at 213 nm. This capability can be used to site-specifically create alaninyl radicals that direct backbone dissociation at the radical site, creating diagnostic d-ions. Furthermore, the additional carbon-sulfur bond fragmentation capability leads to signature triplets for fragmentation of disulfide bonds. Absorption of amide bonds can enhance dissociation of nearby labile carbon-sulfur bonds and can be used for stochastic backbone fragmentation typical of UVPD experiments at shorter wavelengths. Several potential applications of the bond-selective fragmentation chemistry observed at 213 nm are discussed. Graphical Abstract ᅟ.

Traditionally chemical modifications altering molecular skeletons (MSs) were the only solution to modulate material active sites at ground states. According to Runge–Gross theorem, the MS and the adjoint electron‐configuration (MS‐AEC) can be tuned at excited states (ESs), even without chemical modifications. A porphyrinic metal–organic framework PCN‐222 and its metalloporphyrin homologs are used for adsorptive carbon capture both at ground states and with photoexcitation (350–780 nm). Instead of passive photothermal effects, the carbon capture performances of all the adsorbents get promotions. The dominant first ESs with long lifetimes meet the time‐scale of molecular adsorption equilibrium, meanwhile tune the MS‐AEC of the porphyrin ligands to generate new active sites with much more negative electrostatic‐potentials, of which the distribution gradient is crucial for inducing CO2 and can be further modulated by the central‐coordinated metal cations at ground and excited states. This work demonstrates the availability of static ESs and possibility of nonchemical modifications. [ABSTRACT FROM AUTHOR]

Three-coordinate Au(I) complexes with thermally activated delayed fluorescence (TADF) have recently gained experimental attention. However, its luminescence mechanism is elusive. Herein, we have employed density functional theory (DFT), time-dependent DFT (TD-DFT), and QM/MM methods to investigate the excited-state and emission properties of the Au(I) complex in both gas and crystal phases. In both environments, the S1 and T1 emitting states mainly involve HOMO and LUMO and show clear metal-ligand charge transfer and intraligand charge transfer characters. The good spatial separation of HOMO and LUMO minimizes the S1–T1 energy gap, which benefits the reverse intersystem crossing (rISC) from T1 to S1. At 300 K, the rISC rate is faster than the T1 phosphorescence emission, which enables the TADF emission. However, at 77 K, such a rISC process is blocked and TADF disappears; instead, only phosphorescence is recorded experimentally. Importantly, this work highlights the importance of environments in regulating luminescence properties and contributes to understanding the TADF emission of organometallic complexes. [ABSTRACT FROM AUTHOR]