Low-energy Transitions Research Articles

Trimetallic CoAuPd alloy nanoparticles confined in mesoporous MIL-101 with low transition energy for enhanced hydrogen generation from formic acid

Developing efficient and low-cost catalysts with excellent hydrogen generation from formic acid (FA) is highly desired but challenging. Herein, a uniform CoAuPd alloy nanoparticles (NPs) were successfully confined into MIL-101 by a surfactant-free co-reduction method. The elevated stability of Co0 in the protected alloy NPs makes its application in FA dehydrogenation successful. Significantly, the resulting Co0.3Au0.35Pd0.35/MIL-101 composites with the lower consumption of noble metals exhibit the 100% hydrogen selectivity, highest activity and excellent stability toward hydrogen generation from FA without any additive at room temperature. Theoretical results reveal that the enhanced hydrogen generation from FA can be ascribed to the synergistic effects between CoAuPd alloy NPs and MIL-101 frameworks with lowest transition energy between LUMO and HOMO and highest adsorption energy of FA, as compared to the bimetallic alloy NPs. Therefore, the present results open up new avenues for developing cost effective and high-performance catalysts for the generation of hydrogen from FA by using porous MOFs as hosts for non-noble metal based NPs.

Understanding the Optical Properties of Doped and Undoped 9-Armchair Graphene Nanoribbons in Dispersion.

Graphene nanoribbons are one-dimensional stripes of graphene with width- and edge-structure-dependent electronic properties. They can be synthesized bottom-up in solution to obtain precise ribbon geometries. Here we investigate the optical properties of solution-synthesized 9-armchair graphene nanoribbons (9-aGNRs) that are stabilized as dispersions in organic solvents and further fractionated by liquid cascade centrifugation (LCC). Absorption and photoluminescence spectroscopy reveal two near-infrared absorption and emission peaks whose ratios depend on the LCC fraction. Low-temperature single-nanoribbon photoluminescence spectra suggest the presence of two different nanoribbon species. Based on density functional theory (DFT) and time-dependent DFT calculations, the lowest energy transition can be assigned to pristine 9-aGNRs, while 9-aGNRs with edge-defects, caused by incomplete graphitization, result in more blue-shifted transitions and higher Raman D/G-mode ratios. Hole doping of 9-aGNR dispersions with the electron acceptor F4TCNQ leads to concentration dependent bleaching and quenching of the main absorption and emission bands and the appearance of red-shifted, charge-induced absorption features but no additional emission peaks, thus indicating the formation of polarons instead of the predicted trions (charged excitons) in doped 9-aGNRs.

(Invited) Electroluminescence from Single-Walled Carbon Nanotubes with Quantum Defects

Individual single-walled carbon nanotubes with covalent sidewall defects have emerged as a new class of photon sources whose photoluminescence spectra can be tailored by the carbon nanotube chirality and the attached functional group/molecule. Here we present electroluminescence spectroscopy data from single-tube devices based on (7,5) carbon nanotubes, functionalized with dichlorobenzene molecules, and wired to graphene electrodes. We observe electrically generated, defect-induced emissions that are controllable by electrostatic gating and strongly red-shifted compared to emissions from pristine nanotubes. The defect-induced emissions are assigned to excitonic and trionic recombination processes by correlating electroluminescence excitation maps with electrical transport and photoluminescence data. At cryogenic conditions additional, gate-dependent emission lines appear which are assigned to phonon-assisted hot-exciton electroluminescence from quasi-levels. Similar results were obtained with functionalized (6,5) nanotubes. We also compare functionalized (7,5) electroluminescence data with photoluminescence of pristine and functionalized (7,5) nanotubes redox-doped using gold(III) chloride solution. This work shows that electroluminescence excitation is selective toward neutral defect-state configurations with the lowest transition energy, which in combination with gate-control over neutral versus charged defect-state emission leads to high spectral purity.Reference: Min-Ken Li et al., ACS Nano 2022 (doi: 10.1021/acsnano.2c03083) Figure 1

Extraction of rosmarinic acid from Salvia officinalis L. using tunable deep eutectic solvent and its physiochemical properties

AbstractRosmarinic acid (RA) is a phenolic compound known for its remarkable antioxidant, antiallergic, antimicrobial, anticarcinogenic and anti‐inflammatory properties, making it highly valuable for diverse industrial applications such as medicine formulation, cosmetic production and food additives. This study focused on the green extraction of RA and antioxidants from Salvia officinalis L. using deep eutectic solvents (DESs). Various DESs were prepared using choline chloride (ChCl) as the sole hydrogen bond acceptor (HBA) with various hydrogen bond donors (HBDs), including acetic acid (AA), propanoic acid (PA), malonic acid (MA) and ethylene glycol (EG) at different compositions (1:1, 1:2 and 2:1) and water content (0–30%). The resulting clear and homogeneous DESs were characterised by Fourier‐transform infrared (FTIR) analysis, density measurements and Nile red assay to investigate their physicochemical properties. Ultrasound‐assisted extraction was performed with the successfully formed DESs at 70°C for 30 min, using a solid‐solvent ratio of 1:30 g/mL to extract RA and antioxidants from S. officinalis L. leaves. Stable DESs (ChCl‐AA, ChCl‐MA, ChCl‐PA and ChCl‐PG) were formed at the molar ratio of 1:2. The formation of hydrogen bonds in the DESs was confirmed by FTIR spectra (3800–3000 cm−1). The DESs densities decreased with increasing temperature and water content. ChCl‐MA DES was the most polar, with the lowest transition energy, value of 44.672 kcal mol−1. ChCl‐EG DES extract (1:2 molar ratio, 30% water content) yielded the highest RA (49.619 ppm), which is 12.2% higher than the methanol extract. ChCl‐MA DES extract (1:2 molar ratio, 10% water content) showed 11.57% higher antioxidant activity than methanol extract, with an inhibition percentage of 92.663%. Overall, ChCl‐EG (30% water content) and ChCl‐MA (10% water content) at the molar ratio of 1:2 are viable green alternatives to conventional solvents for extracting RA and antioxidants from S. officinalis L., respectively.

Modulation of capacitive energy storage performance in 0.9(Na0.5Bi0.5)(Fe0.02Ti0.98)O3-0.1SrTiO3 relaxor ferroelectric thin film via sol-gel optimizing strategy

0.9(Na0.5Bi0.5)(Fe0.02Ti0.98)O3-0.1SrTiO3 (NBSFT) precursor solutions with varying ratios (1:0, 2:1, 1:1 and 1:2) of C2H6O2 to C3H8O2 are modulated and phase-pure thin films (marked as NBSFT10, NBSFT21, NBSFT11 and NBSFT12) are deposited onto Pt(111)/Ti/SiO2/Si substrate. The hydrolysis of titanate is enhanced with the addition of C3H8O2, which is beneficial for the formation of three-dimension network structure in the sol-gel. The wettability of sol-gel onto the substrate is improved and both the critical radius of new phase and phase transition energy barrier from liquid to solid phases are decreased. All these contribute to fine grain size, even and dense microstructure, and smooth surface for thin films. Besides, the low phase transition energy barrier causes the ion migration with high-efficiency and the increased degree of ion disorder, which is highly relevant to the relaxation behavior of the thin films. Note that the NBSFT11 thin film possesses higher recoverable energy storage density (Wrec) and efficiency (η) of 41.0 J/cm3 and 71.6%, respectively under 3207.6 kV/cm. Excellent thermal stability within the temperature range of 20–220 °C, frequency stability in the range of 1–20 kHz, and fatigue resistance up to 1 × 108 cycles are obtained. These findings provide a novel approach and valuable guidance for designing ferroelectric thin films for energy storage applications.

A potential nonlinear optical material for crown-porphyrin complexes: Alkali metal doping and transition metal introducing

Crown ethers have inspired the rapid growth of research interest in the design and synthesis of functional materials due to their exceptional affinity for metal. In this work, a fascinating crown-porphyrin (Cr-Pr) complexes were studied with doping alkali metal (potassium, K atom) on the crown ether face and introducing transition metal (zinc, Zn atom) on the porphyrin face. The research reveals that the Cr-Pr complex with doped K and Zn atoms results in significant variations in nonlinear optical (NLO) properties. Interestingly, the crown ether ring with the K atom in the K@Cr-Pr complex leads to a remarkable first hyperpolarizability (βtot). On the contrary, when introducing the Zn atom in porphyrins, the Cr-Pr@Zn complex exhibits no significant change in NLO response. Further, the combination of the K and Zn atoms in crown-porphyrin complex (K@Cr-Pr@Zn) can result in significant enhancement of their NLO characteristics, which is much greater than that of the K@Cr-Pr and the Cr-Pr@Zn complexes. The natural population analysis (NPA) and the molecular electrostatic potential maps (ESP) show that the doping of the K atom regulates effectively charge distribution in the complexes. Moreover, the great βtot value can be further illustrated by their low transition energies and an obvious charge transfer (CT) transition in the main excited states. Therefore, the current work achieves that the NLO properties of crown ether derivatives can be regulated by doping alkali metals in the crown ether ring and provides a theoretical guide for developing high-performance NLO devices.

Time-resolved pump–probe spectroscopic ellipsometry of cubic GaN. I. Determination of the dielectric function

An ultra-fast change of the absorption onset for zincblende gallium-nitride (zb-GaN) (fundamental bandgap: 3.23 eV) is observed by investigating the imaginary part of the dielectric function using time-dependent femtosecond pump–probe spectroscopic ellipsometry between 2.9 and 3.7 eV. The 266 nm (4.66 eV) pump pulses induce a large electron–hole pair concentration up to 4×1020cm−3, which shift the transition energy between conduction and valence bands due to many-body effects up to ≈500 meV. Here, the absorption onset increases due to band filling while the bandgap renormalization at the same time decreases the bandgap. Additionally, the absorption of the pump-beam creates a free-carrier profile within the 605 nm zb-GaN layer with high free-carrier concentrations at the surface, and low concentrations at the interface to the substrate. This leads to varying optical properties from the sample surface (high transition energy) to substrate (low transition energy), which are taken into account by grading analysis for an accurate description of the experimental data. For this, a model describing the time- and position-dependent free-carrier concentration is formulated by considering the relaxation, recombination, and diffusion of those carriers. We provide a quantitative analysis of optical experimental data (ellipsometric angles Ψ and Δ) as well as a plot for the time-dependent change of the imaginary part of the dielectric function.

Mixed-Valence Tetrametallic Iridium Chains.

Neutral [X-{Ir2 }-{Ir2 }-X] (X=Cl, Br, SCN, I) and dicationic [L-{Ir2 }-{Ir2 }-L]2+ (L=MeCN, Me2 CO) tetrametallic iridium chains made by connecting two dinuclear {Ir2 } units ({Ir2 }=[Ir2 (μ-OPy)2 (CO)4 ], OPy=2-pyridonate) by an iridium-iridium bond are described. The complexes exhibit fractional averaged oxidation states of +1.5 and electronic delocalization along the metallic chain. While the axial ligands do not significantly affect the metal-metal bond lengths, the metallic chain has a significant impact on the iridium-L/X bond distances. The complexes show free rotation around the unsupported iridium-iridium bond in solution, with a low-energy transition state for the chloride chain. The absorption spectra of these complexes show characteristic bands at 438-504 nm, which can be fine-tuned by varying the terminal capping ligands.

Global supply sustainability assessment of critical metals for clean energy technology

The enduring challenges posed by the supply sustainability of critical metals have long served as a barrier to the low carbon energy transition and the regulation of global climate issues. This study aims to determine whether the supply of essential minerals can keep pace with the global demand associated with the shift towards low-carbon energy sources. In this study, critical metal minerals required by clean energy technology are taken as the research object, the supply and demand background of critical minerals are sorted and compared. By utilizing the genetic algorithm support vector regression (GA-SVR) predictive model, the research scrutinized the supply trends and developed twelve different supply and demand schemes under various development scenarios. These facilitated the assessment of the future supply sustainability of critical metals for clean energy technology. Results demonstrate that under a basic scenario, the global supply of lithium, cobalt, and nickel is projected to reach 200,000 tons, 300,000 tons, and 4 million tons, respectively, by 2030. Under a high supply scenario, these figures rise to 350,000 tons, 500,000 tons, and 5 million tons. From a global supply trend perspective, lithium, cobalt, and nickel resources are projected to grow by 2–4, 1–3, and 1.6–2 times, respectively. Examining supply and demand, the highest risk of supply shortages lies with lithium resources, followed by cobalt. Meanwhile, nickel faces no imminent risk of supply shortage. By 2030, if the compound annual growth rate of global demand for lithium and cobalt hits 15%, supply sustainability will reach a critical juncture, leading to a supply deficit. Lithium resources may encounter this critical demand growth rate even earlier. Although the supply risks for cobalt and nickel currently appear minimal, questions around the long-term availability and sustainability of these resources persist. Ensuring the sustainable supply of these resources necessitates a well-structured and efficient system for recycling secondary resources, technological advancements in the mining industry, and improvements in material strength.

Structures and Spectroscopic Properties of Polysulfide Radical Anions: A Theoretical Perspective.

The potential involvement of polysulfide radical anions Sn•- is a recurring theme in discussions of the basic and applied chemistry of elemental sulfur. However, while the spectroscopic features for n = 2 and 3 are well-established, information on the structures and optical characteristics of the larger congeners (n = 4-8) is sparse. To aid identification of these ephemeral species we have performed PCM-corrected DFT calculations to establish the preferred geometries for Sn•- (n = 4-8) in the polar media in which they are typically generated. TD-DFT calculations were then used to determine the number, nature and energies of the electronic excitations possible for these species. Numerical reliability of the approach was tested by comparison of the predicted and experimental excitation energies found for S2•- and S3•-. The low-energy (near-IR) transitions found for the two acyclic isomers of S4•- (C2h and C2v symmetry) and for S5•- (Cs symmetry) can be understood by extension of the simple HMO π-only chain model that serves for S2•- and S3•-. By contrast, the excitations predicted for the quasi-cyclic structures Sn•- (n = 6-8) are better described in terms of σ → σ* processes within a localized 2c-3e manifold.

^{133}In: A Rosetta Stone for Decays of r-Process Nuclei.

The β decays from both the ground state and a long-lived isomer of ^{133}In were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to β, γ, and neutron spectroscopy, the comparative partial half-lives (logft) have been measured for all their dominant β-decay channels for the first time, including a low-energy Gamow-Teller transition and several first-forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their β decays selectively populate only a few isolated neutron unbound states in ^{133}Sn. Precise energy and branching-ratio measurements of those resonances allow us to benchmark β-decay theories at an unprecedented level in this region of the nuclear chart. The results show good agreement with the newly developed large-scale shell model (LSSM) calculations. The experimental findings establish an archetype for the β decay of neutron-rich nuclei southeast of ^{132}Sn and will serve as a guide for future theoretical development aiming to describe accurately the key β decays in the rapid-neutron capture (r-) process.

Effects of Enol-imine/Keto-amine tautomerism and conformational changes on the electronic spectra of a novel 1,2,4-triazole ortho-hydroxyaryl Schiff base in different solvents

In this study, a novel o-hydroxyaryl Schiff base bearing the 1,2,4-triazole heterocyclic core, (E)-2-(((4H-1,2,4-triazol-4-yl)imino)methyl)-6-methoxyphenol, was synthesized and structurally characterized by NMR (1H- and 13C-) and IR spectroscopies as well as by Density Functional Theory (DFT) electronic structure calculations. The compound was then investigated by UV–Vis absorbance and fluorescence emission spectroscopies in different solvents. The wavelength shifts observed in the band corresponding to the lowest energy transition in the absorbance spectra upon changing the solvent, as well as in the emission bands observed in the fluorescence spectra (upon excitation at 310 nm) were explained considering the effects of solvent-induced conformational changes and photoinduced enol-imine/keto-amine tautomerism. The interpretation of the experimental results was supported by structural data calculated for the different isomeric forms of the compound and of their electronic spectra in the gas phase and in solvents of different polarity. Solvent effects were also evaluated at the light of the Kamlet-Taft and Catalán solvatochromic models.

Mimicking biological synapses with a-HfSiOx-based memristor: implications for artificial intelligence and memory applications

Memristors, owing to their uncomplicated structure and resemblance to biological synapses, are predicted to see increased usage in the domain of artificial intelligence. Additionally, to augment the capacity for multilayer data storage in high-density memory applications, meticulous regulation of quantized conduction with an extremely low transition energy is required. In this work, an a-HfSiOx-based memristor was grown through atomic layer deposition (ALD) and investigated for its electrical and biological properties for use in multilevel switching memory and neuromorphic computing systems. The crystal structure and chemical distribution of the HfSiOx/TaN layers were analyzed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The Pt/a-HfSiOx/TaN memristor was confirmed by transmission electron microscopy (TEM) and showed analog bipolar switching behavior with high endurance stability (1000 cycles), long data retention performance (104 s), and uniform voltage distribution. Its multilevel capability was demonstrated by restricting current compliance (CC) and stopping the reset voltage. The memristor exhibited synaptic properties, such as short-term plasticity, excitatory postsynaptic current (EPSC), spiking-rate-dependent plasticity (SRDP), post-tetanic potentiation (PTP), and paired-pulse facilitation (PPF). Furthermore, it demonstrated 94.6% pattern accuracy in neural network simulations. Thus, a-HfSiOx-based memristors have great potential for use in multilevel memory and neuromorphic computing systems.Graphical

Impact of the Protein Environment on Two-Photon Absorption Cross-Sections of the GFP Chromophore Anion Resolved at the XMCQDPT2 Level of Theory.

The search for fluorescent proteins with large two-photon absorption (TPA) cross-sections and improved brightness is required for their efficient use in bioimaging. Here, we explored the impact of a single-point mutation close to the anionic form of the GFP chromophore on its TPA activity. We considered the lowest-energy transition of EGFP and its modification EGFP T203I. We focused on a methodology for obtaining reliable TPA cross-sections for mutated proteins, based on conformational sampling using molecular dynamics simulations and a high-level XMCQDPT2-based QM/MM approach. We also studied the numerical convergence of the sum-over-states formalism and provide direct evidence for the applicability of the two-level model for calculating TPA cross-sections in EGFP. The calculated values were found to be very sensitive to changes in the permanent dipole moments between the ground and excited states and highly tunable by internal electric field of the protein environment. In the case of the GFP chromophore anion, even a single hydrogen bond was shown to be capable of drastically increasing the TPA cross-section. Such high tunability of the nonlinear photophysical properties of the chromophore anions can be used for the rational design of brighter fluorescent proteins for bioimaging using two-photon laser scanning microscopy.

Legal responses to energy security and sustainability in Nigeria's power sector amidst fossil fuel disruptions and low carbon energy transition

Fundamentally, energy could be refer to as the cornerstone for progress of most nations, as a lack of unswerving energy sources perpetuates poverty and impedes economic development. In Nigeria, there exists an abundance of low-carbon energy resources that hold immense potential for fostering sustainable growth. Regrettably, Nigeria has yet to fully harness these resources to drive its economic expansion and bolster its power sector. This study undertakes a thorough exploration of the untapped capacity of low-carbon energy bases in the country, with the aim of ensuring a consistent and dependable electricity supply. The research methodology employed in this study encompasses both empirical and doctrinal legal research approaches, drawing upon a wide range of primary and secondary sources, including authoritative energy law textbooks and peer-reviewed journals. In order to gain valuable insights into achieving a stable electricity supply in Nigeria, a meticulous comparative legal analysis of low-carbon energy practices was conducted, focusing on the experiences of China, Spain, Germany, and Nigeria. By applying legal theories and empirical procedures, the study estimated carbon emissions using the auto-regressive distributed lag model. The data exploited in this study were acquired from the World Bank's World Development Indicator (WDI, 2021), a renowned public domain repository of economic development data encompassing numerous countries worldwide. The findings of this study demystify the positive association between electricity consumption and substantial fluctuations in CO2 emissions, as demonstrated by both short-run and long-run model estimations. Significantly, the presence of hydroelectric power sources emerged as a pivotal factor in curbing carbon emissions.Moreover, the study's error correction model findings unveil a noteworthy mechanism of systemic convergence when confronted with external shocks. To facilitate the adoption of low-carbon energy sources, the study proposes a hybrid model that combines various approaches, while underscoring the urgent need for reforming Nigeria's energy laws to address environmental concerns and promote security and sustainability. The practical implications and policy applications of this research highlight its potential to provide policymakers in Nigeria and beyond with invaluable insights for formulating effective measures aimed at reducing carbon emissions arising from electricity generation and consumption.

Embarking on the Asia Supergrid: Trade impact of carbon pricing on regional sustainability in northeast Asia

Under the rising pressure for low carbon energy transitions in Northeast Asia (NEA), interconnecting local power grids for interstate power trade allows to share reserve capacity and to redistribute intermittent renewable energy across time zones, contributing to regional sustainability. Using a linear programming model that minimizes total energy system costs to meet hourly power demand, we build a hypothetical electricity transmission model for three urban demand centers interconnecting China, South Korea, and Japan to test economic and environmental competitiveness of the trilateral power trade with carbon pricing. In the economic perspective our results indicate that interstate electricity trade enables cost savings at all levels of CO2 prices tested (0–180USD/ton of CO2 emitted) through more efficient fuel consumptions on an hourly basis at the NEA regional level. However, ambitious carbon pricing (above 90 USD/ton CO2 emitted) is still essential for trade to ensure equitable trade impacts for all participating nodes. While trade utilizes gaps in resource availabilities and technology costs across nodes in cost minimization, results show inadequate carbon pricing leads to extra thermal combustions at the local level although regional total emissions reduce.

Sulfonyl Diazaborine 'Click' Chemistry Enables Rapid and Efficient Bioorthogonal Labeling.

Finding an ideal bioorthogonal reaction that responds to a wide range of biological queries and applications is of great interest in biomedical applications. Rapid diazaborine (DAB) formation in water by the reactions of ortho-carbonyl phenylboronic acid with α-nucleophiles is an attractive conjugation module. Nevertheless, these conjugation reactions demand to satisfy stringent criteria for bioorthogonal applications. Here we show that widely used sulfonyl hydrazide (SHz) offers a stable DAB conjugate by combining with ortho-carbonyl phenylboronic acid at physiological pH, competent for an optimal biorthogonal reaction. Remarkably, the reaction conversion is quantitative and rapid (k2 >103 M-1 s-1 ) at low micromolar concentrations, and it preserves comparable efficacy in a complex biological milieu. DFT calculations support that SHz facilitates DAB formation via the most stable hydrazone intermediate and the lowest energy transition state compared to other biocompatible α-nucleophiles. This conjugation is extremely efficient on living cell surfaces, enabling compelling pretargeted imaging and peptide delivery. We anticipate this work will permit addressing a wide range of cell biology queries and drug discovery platforms exploiting commercially available sulfonyl hydrazide fluorophores and derivatives.

Photoluminescence Enhancement of InSe by Coupling with Circular Bragg Grating

AbstractIndium selenide (InSe) has attracted tremendous research interest due to its excellent optical and electronic properties. The direct bandgap of bulk InSe promises efficient carrier recombination in the near‐infrared (NIR) spectral range, holding great potential for NIR‐based optoelectronic device applications. However, the lowest energy transition in InSe involves out‐of‐plane optical dipoles, with resulting photoluminescence (PL) transmitted mainly along the layer plane. This limits both optical excitation and detection efficiency along the surface normal for practical device operation. To circumvent this issue, here, bulk InSe flake is coupled with circular Bragg grating (CBG) fabricated on silicon substrate by focused ion beam milling. A maximal 60‐fold PL enhancement is achieved, with Purcell effect‐facilitated carrier recombination and improved light out‐coupling via CBG contributing jointly. The same device architecture is further demonstrated to boost the second harmonic generation by a factor of 34. The results provide an effective way to enhance the optical performance of III–VI layered nanomaterials for both linear and nonlinear optoelectronic device applications.

Enhancement in Nonlinear Optical Response of Oligothiophenes by Induction of Polarons

In this study, the electronic and nonlinear optical properties of neutral ((nTh) and polaronic states (nTh*) of oligothiophenes are studied. Electronic properties are evaluated through HOMO–LUMO gap, ionization potential (IP), and electronic affinity (EA). The results of global reactivity descriptors also indicate the stability of nTh*. The linear and nonlinear optical properties are evaluated through the polarizability and static and dynamic hyperpolarizabilities. The polaronic states of these polymers show high hyperpolarizability (βo) up to 2.7 × 104 au as compared to neutral counterparts. This remarkable increase is mainly due to low transition energies arising from the induction of polaron. The NLO response of polaron-based oligothiophenes are much better than their neutral counterparts. Furthermore, the frequency dependent calculations for polaronic state of oligothiophenes (nTh*) are also performed at commonly used laser frequencies of 532 and 1064 nm. The results of frequency dependent calculations reveal that the values of dynamic hyperpolarizability are more pronounced than static hyperpolarizability. Time-dependent calculations show enough transparency of polaronic state of nTh* in the UV region, which reveals that the materials show good NLO response and could be used in the field of optoelectronics.

Relationship between radiative characteristics and molecular geometry: Photophysical analysis of 2-phenylnaphthalene-appended ortho-carboranyl luminophores

This study investigates the photophysical features of aromatic conjugated o-carboranes and provides strong evidence for the relationship between their molecular geometry and photoluminescence efficiency. Four 2-phenylnaphthalene appended o-carboranyl luminophores, each with a different 2-phenyl ring distortion angle (1F, 2P, 3M, and 4I) were prepared and characterized. In particular, the geometric features around the 2-phenyl ring in the crystalline state were fully determined using single-crystal X-ray diffraction. All compounds in rigid states (solution at 77 K and solid states) demonstrated strong intramolecular charge-transfer (ICT)-based emissions in the yellowish-green region. Intriguingly, the quantum efficiency of the ICT-based emission gradually decreased as the distortion of the terminal 2-phenyl ring increased. Furthermore, the radiative decay constant of 1F was five times that of 4I, whereas the nonradiative decay of 1F was less than one-third that of 4I. In addition, theoretical modeling of the low-energy transition in the first excited state of 2P upon the rotation of the 2-phenyl ring revealed that the distorted geometry strongly affects the ICT-based radiative process. This model strongly suggests that the ICT-based radiative efficiency of π‒conjugated o-carborane is significantly affected by the geometry of the appended aromatic group.