Search

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]

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]

Theoretical modeling of the solid‐state photocatalysis is one of the important issues as various useful photocatalysts have been developed to date. In this work, we investigated the mechanism of the alcohol photooxidation on niobium oxide (Nb2O5) which was experimentally developed, using the density functional theory (DFT)/time‐dependent (TD)DFT calculations based on the cluster model. The alcohol adsorption and the first hydrogen transfer from hydroxy group to surface occur in the ground state, while the second hydrogen transfer from CH proceeds in the excited states during the photoirradiation of UV or visible light. The spin crossing was identified and the low‐lying triplet states were solved for the reaction pathway. The photoabsorption in the visible light region was characterized as the charge transfer transition from O 2p of alcohol to Nb 4d of the Nb2O5 surface. The spin density and the natural population analysis indicated the generation of spin density in the moiety of carbonyl compound and its dissipation to the interface of the surface, which partly explains the electron paramagnetic resonance measurement. It was confirmed that the rate determining step is the desorption of carbonyl compound and water molecule in agreement with the experimental rate equation analysis. The present findings with the theoretical modeling will provide useful information for the further studies of the solid‐state photocatalysis. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

Modern computational chemistry methods aid experimentalists in scrutinizing molecular systems for organic optoelectronic device fabrication. They are also helpful for device engineering, such as choosing metals for contact fabrication without sophisticated instrumentation. The B3LYP functional with 6-31G(d,p) or 6-311G(d,p) basis set is a widely used method in this regard. Recently, many upgraded methods, such as the three-fold corrected composite scheme (3C), have been reported to offer cost-effectiveness and better accuracy than the B3LYP. This is particularly interesting from a materials engineering point of view as these methods offer the possibility of rapidly screening the materials prior to the experimental analysis. In order to evaluate their suitability towards organic optoelectronic systems, in this work, we have used three composite schemes, namely B97-3C, PBEh-3C and HF-3C, along with B3LYP and the experimental data. The well-studied tetracene system is considered for the analysis, and different optoelectronic properties such as bandgap, reorganization energy, and absorption maximum are calculated theoretically and compared with the experimental data. The results indicate that though slightly expensive, B3LYP performs better than the 3C methods. Of the three, only PBEh-3C performs on par with B3LYP in accuracy and time. A note of caution is that these results should be inferred as this level of theory is adequate for the screening and modeling optoelectronic systems rather than a potential computational chemistry method. [Display omitted] • B3LYP and three 3C methods are evaluated for the optoelectronic studies. • All produced reasonable geometry, but other properties obtained from HF-3C are unreliable. • B3LYP with 6-31G(d,p) produced favorable performance than the 3C methods. • PBEh-3C outperforms yet computationally more demanding for excited state analysis. • Owing to its less accuracy B97-3C is more suitable for initial geometry optimization. [ABSTRACT FROM AUTHOR]

[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]