Exciton Self-Trapping in sp2 Carbon Nanostructures Induced by Edge Ether Groups

Substituent effects on the ESIPT process and the potential applications in materials transport field of 2'-aminochalcone derivatives

This work investigates the different charge transfer characteristics and excited state intramolecular proton transfer process (ESIPT) of 2'-aminochalcones derivatives carrying different electron-withdrawing groups. Four new molecules are designed in the experiment and named as 2c, 3c, 4c and 5c, respectively. (Dyes and Pigments, 2022, 202.) Based on these four molecules, the effect of substituents on the ESIPT process and the charge transfer process are discussed in detail in our work. According to the study of the related parameters at the hydrogen bond site, infrared vibration spectrum, interaction region indicator isosurface (IRI) and scatter plots, it is concluded that the hydrogen bond interaction is enhanced under photoexcitation, and the descending order of the excited state hydrogen bond strength is 3c > 5c > 4c > 2c. The hydrogen bond energy is calculated by atoms in moleculs (AIM) topological analysis and core-valence bifurcation (CVB) index. The potential energy curve reveals the ESIPT mechanism. Frontier molecular orbital and electron-hole analyses explain the reasons for the changes in the ESIPT process at the electronic level. In addition, the ionization potentials (IPa and IPv), affinity energies (EAa and EAv) and reorganization energies are calculated to evaluate the potential application value of organic molecules in material transport field.

Easy but Efficient: Facile Approach to Molecule with Theoretically Justified Donor-Acceptor Structure for Effective Photothermal Conversion and Intravenous Photothermal Therapy

To accelerate the pace in the field of photothermal therapy (PTT), it is urged to develop easily accessible photothermal agents (PTAs) showing high photothermal conversion efficiency (PCE). As a proof-of-concept, hereby a conventional strategy is presented to prepare donor-acceptor (D-A) structured PTAs through cycloaddition-retroelectrocyclization (CA-RE) reaction, and the resultant PTAs give high PCE upon near-infrared (NIR) irradiation. By joint experimental-theoretical study, these PTAs exhibit prominent D-A structure with strong intramolecular charge transfer (ICT) characteristics and significantly twisting between D and A units which account for the high PCEs. Among them, the DMA-TCNQ exhibits the strongest absorption in NIR range as well as the highest PCE of 91.3% upon irradiation by 760-nm LED lamp (1.2 W cm-2). In vitro and in vivo experimental results revealed that DMA-TCNQ exhibits low dark toxicity and high phototoxicity after IR irradiation along with nude mice tumor inhibition up to 81.0% through intravenous therapy. The findings demonstrate CA-RE reaction as a convenient approach to obtain twisted D-A structured PTAs for effective PTT and probably promote the progress of cancer therapies.

Isomerization of surface functionalized SWCNTs and the critical influence on photoluminescence: static calculations and excited-state dynamics simulations

Single-walled carbon nanotubes (SWCNTs) functionalized with sparse surface chemical groups are promising for a variety of optical applications such as quantum information and bio-imaging. However, the luminescence efficiencies and stability, two key aspects, undoubtedly govern their practical usage. Herein, we assess the surface migration of oxygen and triazine groups on as-modified SWCNT fragments by adopting transition state theory and explore the de-excitation of oxygen-functionalized SWCNT fragments by performing non-adiabatic excited-state dynamics simulations. According to the predicted moderate or even small reaction barriers, the migration of both oxygen and triazine groups is feasible from an sp3 defect configuration forming an energetically more stable sp2 configuration at moderate or even room temperatures. Such isomerization leads to drastically different light emission capabilities as indicated by the large or zero oscillator strengths. During the dynamics simulations, the lowest excited singlet (S1) state rapidly decays in energy within 20 fs and then fluctuates until the end, providing insights into the emission mechanism of SWCNTs. This study highlights the potential intrinsic limitations of surface-functionalized SWCNTs for luminescence applications.

Study of the electronic effect and quantitative spectra predictions of o-methoxyaniline-terminated monoazonaphthols: a combined experimental and DFT study

A combined experimental and density functional theory (DFT) study on the UV-Vis spectra of o-methoxyaniline-terminated mono azo dyes was conducted. By applying time-dependent-DFT calculations, details of excitation processes were determined and visualization by hole-electron analysis was undertaken. Fragment-divided analysis revealed the contributions of different parts of the structures for the UV-Vis spectra, that richer/poorer electron density on aromatic rings lead to greater/less maximum absorption wavelengths (λmax) and larger/smaller half peak width (W1/2). Combining theoretical prediction with experimental verification, we answered the question of how the electronegativities of substituents affected the electron densities and how it affected the spectra. In addition, a linear model connecting the λmax and W1/2 to the chemical shifts obtained by NMR spectroscopy was constructed, which laid the foundation for construction of a spectral library.

The Linkage-Moderated Covalent Organic Frameworks with C=N and NN on Charge Transfer Kinetics Towards the Robust Photocatalytic Hydrogen Activity

Since the linkages structured in covalent organic frameworks (COFs) usually impact the charge transfer behavior during photocatalytic hydrogen evolution reaction (pc-HER), linkage dependence on charge transfer kinetics should be further claimed. Herein, COFs with N-based linkages and pyrene-based building nodes are constructed to enable us to obtain new clues about the charge transfer behavior and evolution tendency relevant to linkages at a molecular level for pc-HER. It is demonstrated that photo-excited electrons preferably move to the N sites in C=N linkage for pc-HER and are trapped around NN linkage as well. A high electron transfer rate does not point to high photocatalytic activity directly, while a small difference between the electron transfer rate and electron recombination rate ΔkCT - CR predicts the inefficiency of charge transfer in Azod-COFs. Contrarily, large value of ΔkCT - CR in the case of Benzd-COFs, demonstrats an unimpeded charge transfer process to result in boosted pc-HER rate (2027.3 µmol h-1 g-1 ). This work offers a prominent strategy for the reasonable design of efficient photocatalysts at the molecular level for structural regulation and achieves an efficient charge transfer process for the pc-HER process.

Heteroleptic Silver(I) and Gold(I) N-Heterocyclic Carbene Complexes: Structural Characterization, Computational Analysis, Tyrosinase Inhibitory, and Biological Effects

Derivatization of (NHC)M-Cl (M = Ag, Au) with selected sulfur donors from the family of dialkyldithiophosphates and bis(2-mercapto-1-methylimidazolyl)borate ligands gave a series of heteroleptic mononuclear complexes. In single-crystal X-ray diffraction analysis, Ag(I) complexes adopted a trigonal planar geometry, while Au(I) complexes are near-linear. TD-DFT and hole-electron analyses of the selected complexes gave insight into the electronic features of the metal complexes. In vitro cellular tests were conducted on the human cancerous breast cell line MCF-7 using 2 and 8. The antibacterial activities of complexes 1, 2, 3, 7, 8, and IPr-Ag-Cl were also screened against Gram-positive (Staphylococcus aureus PTCC 1112) and Gram-negative (Escherichia coli PTCC 1330) bacteria. Antityrosinase and hemolytic effects of the selected compounds were also determined.

Effect of steric hindrance and number of substituents on the transfer and interface properties of Y-shaped hole-transporting materials for perovskite solar cells

Alkyl sulfoxide groups were introduced into the branch chain terminals of a hole-transporting material (HTM) Z34 with different numbers and positions to design four new Y-shaped HTMs: ZT1, ZT2, ZT3 and ZT4. The effects of steric hindrance and number of substituents on the transfer and interface properties of the Y-shaped HTMs were investigated theoretically. Calculations reveal that the introduction of alkyl sulfoxide increases the distribution of intramolecular holes and orbital overlap between the HOMOs of the dimers. The electronic coupling was greatly improved owing to the increased distribution of holes and orbital overlap. ZT1 shows small steric hindrance when one alkyl sulfoxide is introduced into the top branch chain, which leads to translation π-π stacking. ZT2 and ZT4 show slightly greater steric hindrance when two or four alkyl sulfoxide groups are introduced into the side branch chains, which leads to face-to-face stacking. While ZT3 shows large steric hindrance when three alkyl sulfoxide groups are introduced into the top and side branch chains, which causes head-to-head stacking. With the increase in number of alkyl sulfoxide groups, the steric hindrance of the molecule increases and the hole mobility decreases. ZT1 achieves the highest hole mobility (2.63 × 10-2 m2 V-1 s-1) that is two orders of magnitude higher than that of Z34 (1.36 × 10-4 m2 V-1 s-1) owing to the optimal balance between the number of alkyl sulfoxide groups and steric hindrance. The HTM/CH3NH3PbI3 adsorbed system was also simulated to characterize the interface properties. Enhanced interface interaction was achieved in the HTM/perovskite systems of ZT2 and ZT3. The orbital distribution of the HTM/perovskite cluster indicates that the new HTMs can promote hole migration and prevent internal electron-hole recombination. The present work not only evaluates the reliable relationship between the structure and properties of new HTMs, but also provides a valuable design strategy for efficient Y-shaped HTMs.

Poly(ionic liquid)s for Photo-Driven CO2 Cycloaddition: Electron Donor-Acceptor Segments Matter

CO₂ cycloaddition with epoxides is a key catalytic procedure for CO₂ utilization. Several metal-based catalysts with cocatalysts are developed for photo-driven CO₂ cycloaddition, while facing difficulties in product purification and continuous reaction. Here, poly(ionic liquid)s are proposed as metal-free catalysts for photo-driven CO₂ cycloaddition without cocatalysts. A series of poly(ionic liquid)s with donor-acceptor segments are fabricated and their photo-driven catalytic performance (conversion rate of 83.5% for glycidyl phenyl ether) outstrips (≈4.9 times) their thermal-driven catalytic performance (17.2%) at the same temperature. Mechanism studies confirm that photo-induced charge separation is promoted by the donor-acceptor segments and can accelerate the CO₂ cycloaddition reaction. This work paves the way for the further use of poly(ionic liquid)s as catalysts in photo-driven CO₂ cycloaddition.

Tuning functionalized hexagonal boron nitride quantum dots for full visible-light fluorescence emission

Tunable photoluminescence has been observed in hexagonal boron nitride quantum dots (BNQDs), but the underlying luminescence mechanism remains elusive. In this study, we examine excited-state properties of several functionalized BNQDs models using density functional theory (DFT), time-dependent DFT, and multistate complete active space second-order perturbation theory (MS-CASPT2) methods. Unlike reported graphene quantum dots, photoluminescence of BNQDs is not affected by their sizes (<2.5 nm). Instead, the embedded single sp³ carbon atom connecting different functional groups can tune emission colors of BNQDs, whose emission wavelength cover full range of visible light and even extend toward near-infrared region. Further analysis reveals that both exciton self-trapping and electron-hole separation decrease HOMO-LUMO energy gaps, leading to large Stokes shifts. Moreover, uneven and even hybridizations induce blue- and red-shifted emission spectra. These findings provide novel insights into full-spectrum emission of BNQDs modified with functional groups.

Understanding the interaction of nucleotides with UVC light: an insight from quantum chemical calculation-based findings

Short-wave ultraviolet (also called UVC) irradiation is a well-adopted method of viral inactivation due to its ability to damage genetic material. A fundamental problem with the UVC inactivation method is that its mechanism of action on viruses is still unknown at the molecular level. To address this problem, herein we investigate the response mechanism of genome materials to UVC light by means of quantum chemical calculations. The spectral properties of four nucleotides, namely, adenine, cytosine, guanine, and uracil, are mainly focused on. Meanwhile, the transition state and reaction rate constant of uracil molecules are also considered to demonstrate the difficulty level of adjacent nucleotide reaction without and with UVC irradiation. The results show that the peak wavelengths are 248.7 nm, 226.1 nm (252.7 nm), 248.3 nm, and 205.8 nm (249.2 nm) for adenine, cytosine, guanine, and uracil nucleotides, respectively. Besides, the reaction rate constants of uracil molecules are 6.419 × 10^-49 s^-1 M^-1 and 5.436 × 10¹¹ s^-1 M^-1 for the ground state and excited state, respectively. Their corresponding half-life values are 1.56 × 10⁴⁸ s and 1.84 × 10^-12 s. This directly suggests that the molecular reaction between nucleotides is a photochemical process and the reaction without UVC irradiation almost cannot occur.

Steric Hindrance Governs the Photoinduced Structural Planarization of Cycloparaphenylene Materials

Cycloparaphenylenes ([n]CPPs) and their derivatives are known for the unique size-dependent photophysical properties, which are largely attributed to the structural planarization-associated exciton localization, attracting substantial research attention. In this work, we show that the steric hindrance between neighboring structural units plays a key role in governing the photoinduced global/local structural planarization and electron-hole distribution features of [n]CPP materials, due to the tunable strength of H···H repulsion between neighboring units via structural modification or C-H distance variation as revealed by density functional theory (DFT) and time-dependent DFT calculations. According to our results, steric hindrance controls the manner and also the extent of excited-state structural planarization, where a weak (strong) steric hindrance favors (hinders) structural planarization upon relaxation in the first excited singlet (S₁) state as compared to the ground (S₀)-state structure. Depending on the molecular structures, steric hindrance leads to fully delocalized, partially separated, or more localized electron-hole distributions. For example, via H···H repulsion release by manually shortening the C-H distance or by chemical substitution of C-H with N atoms, the modified [10]CPP structures show fully planarized configurations (each dihedral angle can be less than 2°) and entirely delocalized electron-hole distribution upon photorelaxation. This work provides insights into the structural origin of the unusual photophysical properties of [n]CPPs and shows the promise of steric hindrance tuning in accessing diverse excited-state features in [n]CPP materials.

Revealing and Tuning the Photophysics of C=N Containing Photothermal Molecules: Excited State Dynamics Simulations

Molecular photothermal conversion materials are recently attracting increasing attention for phototherapy applications. Herein we investigate the excitation and de-excitation processes of a photothermal molecule (C1TI) that is among the recently developed class of small-molecule-based photothermal imines with superb photothermal conversion efficiencies (PTCEs) up to 90% and a molecule (M2) that is constructed by replacing the amino group of C1TI with an H atom, via excited-state dynamics simulations based on the time-dependent density functional theory (TD-DFT). The simulations reveal fast (<150 fs of average time) nonradiative decays of the lowest excited singlet (S1) state to a conical intersection (CI) with the ground (S0) state in high yields (C1TI: 93.9% and M2: 87.1%). The fast decays, driven by C=N bond rotation to a perpendicular structural configuration, are found to be barrierless. The slight structural difference between C1TI and M2 leads to drastically different S0-S1 energy surfaces, especially M2 features a relatively much lower CI (0.8 eV in energy) and much more decay energy (1.0 eV) to approach the CI. This work provides insights into the de-excitation mechanisms and the performance tuning of C=N enabled photothermal materials.

Carbon Nanodots from an In Silico Perspective

Carbon nanodots (CNDs) are the latest and most shining rising stars among photoluminescent (PL) nanomaterials. These carbon-based surface-passivated nanostructures compete with other related PL materials, including traditional semiconductor quantum dots and organic dyes, with a long list of benefits and emerging applications. Advantages of CNDs include tunable inherent optical properties and high photostability, rich possibilities for surface functionalization and doping, dispersibility, low toxicity, and viable synthesis (top-down and bottom-up) from organic materials. CNDs can be applied to biomedicine including imaging and sensing, drug-delivery, photodynamic therapy, photocatalysis but also to energy harvesting in solar cells and as LEDs. More applications are reported continuously, making this already a research field of its own. Understanding of the properties of CNDs requires one to go to the levels of electrons, atoms, molecules, and nanostructures at different scales using modern molecular modeling and to correlate it tightly with experiments. This review highlights different in silico techniques and studies, from quantum chemistry to the mesoscale, with particular reference to carbon nanodots, carbonaceous nanoparticles whose structural and photophysical properties are not fully elucidated. The role of experimental investigation is also presented. Hereby, we hope to encourage the reader to investigate CNDs and to apply virtual chemistry to obtain further insights needed to customize these amazing systems for novel prospective applications.

In situ photodeposition of platinum clusters on a covalent organic framework for photocatalytic hydrogen production

Photocatalytic hydrogen production has been considered a promising approach to obtain green hydrogen energy. Crystalline porous materials have arisen as key photocatalysts for efficient hydrogen production. Here, we report a strategy to in situ photodeposit platinum clusters as cocatalyst on a covalent organic framework, which makes it an efficient photocatalyst for light-driven hydrogen evolution. Periodically dispersed adsorption sites of platinum species are constructed by introducing adjacent hydroxyl group and imine-N in the region of the covalent organic framework structural unit where photogenerated electrons converge, leading to the in situ reduction of the adsorbed platinum species into metal clusters by photogenerated electrons. The widespread platinum clusters on the covalent organic framework expose large active surface and greatly facilitate the electron transfer, finally contributing to a high photocatalytic hydrogen evolution rate of 42432 μmol g⁻¹ h⁻¹ at 1 wt% platinum loading. This work provides a direction for structural design on covalent organic frameworks to precisely manipulate cocatalyst morphologies and positions at the atomic level for developing efficient photocatalysts.

Porous covalent organic frameworks have arisen as tunable photocatalysts for H₂ production. Here, authors report frameworks engineered with co-catalyst binding sites to improve photocatalytic H₂ evolution performances.

Roles of alkali metal dopants and surface defects on polymeric carbon nitride in photocatalytic peroxymonosulfate activation towards water decontamination

Polymeric carbon nitride (PCN) has been extensively employed in peroxymonosulfate (PMS) activation for water decontamination. However, limited photocatalytic efficiency can be achieved by pristine PCN due to its intrinsic deficiencies like high electron-hole recombination rate and resistance to charge transfer. Herein, in a two-stage thermal treatment process, the nontoxic and stable Na and K were successfully anchored among the PCN skeleton with surface defects created, leading to an elevated photocatalytic activity for PMS activation. The SO₄·^- and ¹O₂ were identified as the dominant reactive oxygen species, which were generated from electron transfer processes between PMS and catalyst. Experimental and theoretical analyses suggested that the defective structures and metal dopants improved the optical properties of catalyst, endowing it a wider light absorption range and a lower energy barrier for electron transitions. The modified structures were also beneficial to electron transfer processes due to the weaker electron confinement effect, accelerating the production of SO₄·^- on the defective sites and ¹O₂ on the metal sites. The synergy of radical and non-radical species weakened the influence of side reactions between radicals from PMS and coexisting inorganic anions in practical water, hence to promote the resistance of modified catalysts in complex water matrices.

Remarkable static and dynamic nonlinear optical responses of Al13-TCNQ/F4-TCNQ complexes: a quantum chemical study

Al13-TCNQ/F4-TCNQ complexes, which exhibit excellent stability and first hyperpolarizabilities, can be considered as candidates for UV and IR NLO materials.

Novel Third-Order Nonlinear Optical Materials with Craig-Möbius Aromaticity

Electron delocalization in aromatic materials significantly impacts their third-order nonlinear optics (NLO). Despite organometallic complexes with Craig-Möbius aromaticity attracting great attention for their unusual physicochemical properties, their third-order NLO have been little studied to date. Herein, 12 Craig-Möbius aromatic organometallics with a stable structure similar to osmapentalyne, namely, carbolong complexes, are screened by DFT. They exhibit high third-order NLO responses because of the d and p electron delocalization in the organometallic ring. Furthermore, electron-hole distribution analyses draw a conclusion that extending the conjugated plane will increase the π-conjugation system to enhance the local excitation in the plane, and the introduction of typical aromatic ligands can result in the organometallic ring-to-ligand charge transfer (RLCT), which are effective methods to improve the third-order NLO response. This study opens a new window in the application of Craig-Möbius aromatic complexes and provides a new approach for third-order NLO materials design.

Thermally activated delayed fluorescence materials with aggregation-induced emission properties: a QM/MM study

Organic molecules with thermally activated delayed fluorescence (TADF) and aggregation induced emission (AIE) properties have attracted increasing research interest due to their great potential applications in organic light emitting diodes (OLEDs), especially for those with multicolor mechanochromic luminescence (MCL) features. Theoretical research on the luminescence characteristics of organic TADF emitters based on the aggregation states is highly desired to quantify the relationship between the TADF properties and aggregation states. In this work, we study the 4,4'-(6-(9,9-dimethylacridine-10(9H)-yl)quinoline-2,3-dibenzonitrile (DMAC-CNQ) emitter with TADF and AIE properties, and calculate the photophysical properties in gas, solid and amorphous states by using the quantum mechanics and molecular mechanics (QM/MM) method. Our simulations demonstrate that the aggregation states enhance obviously the reverse intersystem crossing rates and transition dipole moments of the DMAC-CNQ emitter, and suppress the non-radiative rates from the lowest excited singlet state (S₁) to ground state (S₀). Specifically, the molecular stacking of DMAC-CNQ in solid phases can mainly restrict the geometric torsion of the DMAC moiety for decreasing non-radiative decay rates, and the torsion of the CNQ moiety for increasing the reverse intersystem crossing rates. As a result, the calculated fluorescence efficiencies of the DMAC-CNQ emitter in the crystal and amorphous states are 67% and 26% respectively, and in good agreement with the experimental results.

Revealing the tunability of electronic structures and optical properties of novel SWCNT derivatives, phenine nanotubes

Single-walled carbon nanotubes (SWCNTs) have evoked great interest for various luminescent applications, but the large emission heterogeneity resulting from the structural complexity of the samples seriously restricts their further development. Herein we theoretically explore the electronic structures and optical properties of phenine nanotubes (pNTs), which are typical luminescent SWCNT derivatives with determined molecular structures that have been synthesized recently (Z. Sun, K. Ikemoto, T. M. Fukunaga, T. Koretsune, R. Arita, S. Sato and H. Isobe, Science, 2019, 363, 151-155; K. Ikemoto, S. Yang, H. Naito, M. Kotani, S. Sato and H. Isobe, Nat. Commun., 2020, 11, 1807). Interestingly, pNTs are found to feature different semiconducting properties to SWCNTs, as indicated by a spatial separation trend in the HOMO and LUMO resulting from periodic structural vacancies. The HOMO-LUMO and optical gaps of pNTs depend inversely on their lengths and diameters, but diameter variation should be an ineffective method for property tuning due to its negligible influence. By contrast, chemical modifications via N doping or hydrogenation highly affect the HOMO-LUMO gaps and their distributions and greatly broaden the light absorption/emission range, and importantly, low-dose hydrogenation is predicted to be a feasible strategy to enhance luminescence. This work, by studying the fundamental photophysical properties of pNTs and making comparisons to SWCNTs, shows the promise of structural vacancy engineering and surface functionalization in acquiring multifunctional tube-like materials.

Insights into the photocatalytic peroxymonosulfate activation over defective boron-doped carbon nitride for efficient pollutants degradation

The metal-free graphitic carbon nitride is a promising photocatalyst for peroxymonosulfate (PMS) activation towards water decontamination, but bearing low efficiency due to its electronic structure and surface chemistry. Herein, the non-metallic element boron was adopted for catalyst development. The boron dopants and defects were simultaneously introduced by potassium borohydride, resulting in an excellent activity towards PMS activation. The dominant reactive oxygen species was singlet oxygen, which was determined to originate from PMS activation over photo-induced holes initiated by an electron transfer process. Calculations based on density functional theory revealed that at excited states, due to the dopants and defects, the electron-hole distribution was altered from an even population to a significant separation, which was beneficial for photocatalytic performance. Besides, the engineered electronic structure weakened the catalyst resistance to charge transfer, enabling easier electron transfer between the catalyst and the PMS. Moreover, the strengthened and enlarged positive electrostatic potential areas on heptazine rings oriented the electron transfer process from the negatively charged PMS to the catalyst, facilitating the generation of singlet oxygen. These findings provide underlying mechanism insights into the contribution of dopants and defects to catalytic performance on persulfate-based photocatalytic water treatment.

Tin Metal Cluster Compounds as New Third-Order Nonlinear Optical Materials by Computational Study

It is quite appealing but challenging to predict and synthesize new nonlinear optical (NLO) materials with exceptional performance. Herein, the different Sn₄ cluster core structures and third-order NLO properties are studied through electronic structure, excited hole-electron, bonding character, and aromaticity analysis. As a result, Sn₄ clusters with ring core structure (Sn₄-R) not only have the smallest E_gap, the largest UV-vis response intensity, but also the strongest third-order NLO response in our work. As proved by natural bond orbitals' (NBO) analysis, electron localization function (ELF), and adaptive natural density partitioning (AdNDP), the Sn₄⁴⁺ has two in-plane four center-two electron (4c-2e) Sn-Sn σ-bonds, resulting in a good delocalization. For the first time, delocalization of metal cluster cores in tin clusters that is beneficial to the third-order NLO response is proposed, which provides a new guidance to design and prepare third-order NLO materials.

Theoretical and Experimental Insights into the Self-Assembly and Ion Response Mechanisms of Tripodal Quinolinamido-Based Supramolecular Organogels

The exploration and understanding of self-assembly and stimuli-responsive mechanisms of supramolecular systems are of fundamental importance for researchers to plan syntheses reasonably. Herein, the self-assembly and ions responsive mechanisms of a tripodal quinolinamido-based supramolecular organogel (TBT-gel) were investigated through experiments and theoretical calculations including independent gradient model (IGM), localized orbitals locator (LOL) and hole-electron theory. According to these studies, the self-assembly mechanism of TBT-gel was based on strong threefold H-bonding and π-π interactions, which induced the TBT forming helical, one-dimensional supramolecular polymer. After addition of Fe³⁺ into the TBT-gel, the one-dimensional supramolecular polymer had been crosslinked by the Fe³⁺ through coordination interaction and formed a metallogel (TBT-Fe-gel). Interestingly, the TBT-gel showed selective fluorescent response for Fe³⁺ and F^- based on a competitive coordination mechanism. Moreover, the study on fluorescence responsive mechanism of TBT-gel for Fe³⁺ and F^- implied the ICT mode governs both the electron excitation and de-excitation processes. The calculated results were in agreement with the corresponding experimental results. Notably, the quantum chemical calculations provided a deep understanding and visualized presentation of the assembly and stimuli-responsive mechanisms.

Revealing the role of nitrogen dopants in tuning the electronic and optical properties of graphene quantum dots via a TD-DFT study

Graphene quantum dots (GQDs) have been suggested to have a wide range of applications due to their unique electronic and optical properties. Moreover, heteroatom doping has become a viable way to fine-tune the properties of GQDs. However, the working principle of the doping strategy is still not conclusive. In this study, the effects of size, configuration of the nitrogen dopant, and N/C ratio on the electronic and optical properties of GQDs have been carefully examined. First, the variation of the adsorption wavelength of pristine GQDs was evaluated for which a linear relation is established against different diameters. Moreover, it is found that both the configuration and content of nitrogen dopants have a significant impact on the adsorption wavelength and band gap of GQDs. In particular, different nitrogen species could have exactly opposite effects on the adsorption behavior. The origin of the nitrogen doping effect is calibrated from orbital localization, charge analysis, natural transition orbitals, and atomic contribution towards excitation. It is noted that nitrogen doping can simultaneously reduce both light adsorption energy and emission energy compared with the pristine one. This study provides an insightful explanation for the electronic and optical properties of GQDs and consolidates the theory base of the doping strategy.

Photoninduced charge redistribution of graphene determined by edge structures in the infrared region

By using the ab initio density-functional theory method, we investigated the charge redistribution of monolayer graphene with ZigZag and/or ArmChair edges upon infrared excitation. The photoinduced charge redistribution is strongly dependent on edge types. The priority of electrons transfer has been revealed by charge density difference. To further investigate the influence of edge types on optical properties, the dielectric constants and absorption coefficient of graphene with various edge types have been calculated. The edge types have a non-negligible influence on optical properties of graphene, and the Zigzag edge graphene owns stronger optical absorption in infrared region. Our results are potentially beneficial for designing graphene nanodevices in the infrared region.

PtSe2/SiH van der Waals type-II heterostructure: a high efficiency photocatalyst for water splitting

PtSe₂/SiH type-II van der Waals heterostructure is a highly efficient photocatalyst for water splitting in visible light.

Reconsider the fluorescence properties of 5-ASA and its sensing mechanism for iodide ion

5-ASA shows multiple fluorescence peaks at 408 nm, 480 nm and 500 nm in methanol solution, which can serve as ratiometric sensor for I^-. However, fluorescence mechanism of 5-ASA remains controversial and I^- detecting mechanism is unclear. With the aid of density functional theory and time-dependent density functional theory, this paper has carried out detailed investigations on both aspects at the molecular level. The origins of all the fluorescence peaks of 5-ASA have been assigned and a new fluorescence mechanism is proposed, which is convincing and intrinsically different from previously proposed mechanisms. Based on the new fluorescence mechanism, the I^- detecting mechanism is fully addressed. Two I^- detecting mechanisms have been proposed and are likely to coexist which lead to the sensitive detection of I^-.

Is Excited-State Aromaticity a Driving Force for Planarization of Dibenzannelated 8π-Electron Heterocycles?

Compounds with dibenzannelated heterocycles with eight π-electrons are found in a range of applications. These molecules often adopt a bent structure in the ground state (S₀ ) but can become planar in the first excited states (S₁ and T₁ ) because of the cyclically conjugated 4nπ central ring, which fulfils the requirements for excited state aromaticity. We report on a quantum chemical investigation of the aromatic character in the S₁ and T₁ states of dibenzannelated seven- and six-membered heterocycles with one, two, or three heteroatoms in the 8π-electron ring. These states could have ππ* or nπ* character. We find that compounds with one or two heteroatoms in the central ring have ππ* states as their S₁ and T₁ states. They are to a significant degree influenced by excited state aromaticity, and their optimal structures are planar or nearly planar. Among the heteroatoms, nitrogen provides for the strongest excited state aromaticity whereas oxygen provides for the weakest, following the established trend of the S₀ state. Yet, dibenzannelated seven-membered-ring compounds with N=N bonds have non-aromatic nπ* states with strongly puckered structures as their S₁ and T₁ states.