Types Of Electronic Transitions Research Articles

Cycloaddition reaction of methylidyne radical with dipyrromethanol: quantum chemical insights into the formation of di(pyridin-2-yl)methanol

Density functional theory was employed to investigate methylidyne radical reaction on to the unsaturation of dipyrromethanol moiety through cycloaddition forming a six membered di(pyridin-2-yl)methanol followed by H-elimination via ring expansion. Time-dependent density functional theory (TD-DFT) simulations were performed to figure out the ultraviolet–visible spectrum of dipyrromethanol and di(pyridin-2-yl)methanol. Ultraviolet–visible spectrum of dipyrromethanol and di(pyridin-2-yl)methanol shows that two sharp absorption peaks were obtained at λ max = 161 nm and 206 nm for the reactant dipyrromethanol while a sharp peak was observed for the product di(pyridin-2-yl)methanol at shorter wavelength (λ max = 170 nm). The theoretical IR spectrum of dipyrromethanol and di(pyridin-2-yl)methanol shows that a significant red shift of 129 cm−1 was observed in the case of di(pyridin-2-yl)methanol due to presence of two strong intra-molecular hydrogen bonds, which indicates its higher stability than the dipyrromethanol. HOMO–LUMO energy gap calculations and natural bond orbital (NBO) analysis endorse the type of electronic transition for the desired product di(pyridin-2-yl)methanol is π–π*. The global reactivity analysis shows the electron donor and acceptor nature of dipyrromethanol and methylidyne radical, respectively. A potential energy surface is constructed via methylidyne radical addition, ring expansion, and hydrogen elimination transition states. Thermodynamics study and potential energy surface of the title reaction indicates its highly exothermicity and spontaneous in nature.

Copper(II) complexes of 1,3-dimethyl-(5-(8′-quinolinylazo)-6-aminouracil: Structures, magnetism and biological activity

Two Cu(II)-complexes were synthesized using 1,3-dimethyl-5-(8′-quinolinylazo)-6-aminouracil (H2L) ligand in combination with thiocyanide (SCN−) and azide (N3−) pseudohalides as co-ligands. The thiocyanide (SCN−) co-ligand guided to form monomeric aquo-isothiocyanato-Cu(II) complex, [CuII(HL)(NCS)(H2O)] (1) of H2L. Under similar reaction condition, the azide (N3−) co-ligand led to form polymeric azido-Cu(II) complex, [CuII(L′)(N3)]n, (2) of HL′, where HL′ was an in-situ generated new ligand, 1,3-dimethyl-(5-(8′-quinolinylazo)-6-hydroxouracil (HL′) from H2L. Both are tridentate ligands with different uracil-donor sites (H2L: NqNaNu, HL′: NqNaOu). The complexes are monoclinic with space groups C2/c (Z = 8) and P21/n (Z = 4) for 1 and 2, respectively. They possess slightly distorted square-pyramidal coordination around CuII ions with elongation at the axial sites (Cu1-O3 (water) bond is 2.2698(13)Å for 1 and Cu1-Oμ-uracil bond is 2.5525(13)Å for 2). The polymeric nature of 2 is availed through one of the exocyclic-C = O groups of HL′, making Cu…Cu spacing to 7.9973(3)Å. Direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 1 and 2 were carried out in the temperature range 1.8-300 K. The 1 is devoid of any significant interaction between the mononuclear units. Magnetic properties show weak ferromagnetic exchange coupling within the chain (J = 0.61 cm−1) in 2. The TD-DFT study reveals that ILCT, LMCT and d-d types of electronic transitions are involved in both the complexes. The evaluated biological efficacy of the compounds against plant pathogens it is revealed that the complex 1 has an antibacterial and complex 2 has antifungal properties.

Theoretical insights into dopamine photochemistry adsorbed on graphene-type nanostructures.

The equilibrium geometry structures and light absorption properties of the dopamine (DA) and dopamine-o-quinone (DAQ) adsorbed on the graphene surface have been investigated using the ground state and linear-response time-dependent density functional theories. Two types of graphene systems were considered, a rectangular form of hexagonal lattice with optimized C-C bond length as the model system for graphene nanoparticles (GrNP) and a similar system but with fixed C-C bond length (1.42 Å) as the model system for graphene 2D sheet (GrS). The analysis of the vertical excitations showed that three types of electronic transitions are possible, namely, localized on graphene, localized on the DA or DAQ, and charge transfer (CT). In the case of the graphene-DA complex, the charge transfer excitations were characterized by the molecule-to-surface (MSCT) character, whereas the graphene-DAQ was characterized by the reverse, i.e. surface-to-molecule (SMCT). The difference between the two cases is given by the presence of an energetically low-lying unoccupied orbital (LUMO+1) that allows charge transfer from the surface to the molecule in the case of DAQ. However, it was also shown that the fingerprints of excited electronic states associated with the adsorbed molecules cannot be seen in the spectrum, as they are mostly suppressed by the characteristic spectral shape of graphene.

Investigation of γ‐irradiation dependent structural properties of LLM‐105 by ultraviolet‐visible diffuse reflectance spectroscopy

AbstractIn this work, different doses of γ‐irradiation were applied to 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) to examine the way in which their optical properties and electronic structure can be affected. The UV absorption spectrum of LLM‐105 was calculated based on the time‐dependent density functional theory (TD‐DFT). The analyses of hole‐electron distribution and charge‐transfer spectra (CTS) revealed the type of electronic transitions and elucidated the nature of each excited state in the LLM‐105 molecule. For the pristine LLM‐105, the band gap (Eg) value of 2.76 eV was obtained using the Kubelka‐Munk model. Moreover, the band gap of LLM‐105 increased with the irradiation dose. The increase in relevant UV‐Vis absorption peak intensity, implying the increase in band gap is due to the formation of a larger conjugated structure in LLM‐105 under γ‐irradiation.

Optical and microscopic characterizations of polyethylene oxides (PEO) doped with nickel nitrate (NiNO₃) transition metal salt

This study used a solution cast process to prepare a PEO doped with (4, 8 and 12 wt%) NiNO3 metal salt. Techniques including FTIR, optical microscope (OM), and UV–Visible-absorption spectrometry were employed to examine the structural, microscopic configuration and optical behaviors of the electrolyte. The FTIR bands indicated shifting and narrowing of PEO-O-H stretching bands by addition of 4w%NiNO3, suggesting a good interaction between the NiNO3 and the polymer. The optical microscope images showed the dark regions ascribed to amorphous phases and it is more dominant in the doped films than in the pure films. According to the optical absorption measurements optimum absorption and transmission of UV–visible light were observed at 4 wt% filler loading. Absorbance and transmittance of PEO were amplified by integrating 4 wt%NiNO3, although concentration above 4 wt% had insignificant influence on the optical behavior of PEO. The PEO:4w% NiNO3 films showed a higher value of refractive index and a greater optical conductivity in the UV wavelength which confirmed the presence of more charge carriers in the doped film. The regions attributed to band gap width and the different types of electron transitions were identified by using the Tauc's model in detail. The absorption edge shifting was distinguished for the 4 wt% doped PEO, and the optical band gap was reduced from 5.25 eV to 4.2 eV.

(Invited) Computational Approach for Materials Design and Comprehensive Understanding of Organic Light-Emitting Diode

Reverse intersystem crossing (RISC) has been the rate-limiting process in thermally activated delayed fluorescence (TADF)[1,2], and has induced material degradation. Therefore, the acceleration of RISC is important for obtaining further excellent TADF-based organic light-emitting diodes (OLEDs), especially for solving the efficiency roll-off problem and extending the device lifetime. Here, we will present three different ways to accelerate RISC; 1) intervening locally excited (LE) state(s) between charge transfer-type S1 (1CT) and CT-type T1 (3CT) [3], 2) using the heavy atom effect [4], and 3) using fluctuation effect that can achieve effective RISC even between 1CT and 3CT [5].Next, we will propose a method to quantitatively predict rate constants of all electronic transitions related to emission[6-8]. TADF molecules have been designed through the calculations of ΔE ST and oscillator strength. However, to develop further excellent emitters, it is desired to precisely calculate the rate constants. Our method based on Fermi’s golden rule allows us to theoretically predict relevant rate constants for all types of electronic transitions in emitter molecules. If the rate constants can be quantified, all quantum yields can be also quantified. The emission mechanism and photophysical performance are also fully understood. We have applied this method to benzophenone and a multiple resonance TADF material, DABNA-1. The calculated rate constants were in quantitative agreement with the experimental ones in both cases. The method was further applied to a very fast RISC molecule, MCz-TXO. Our method quantitatively reproduced the experimentally-obtained very large k RISC of 108 s-1 caused by the heavy atom effect of sulfur (S). We can expect much larger k RISC when we use much heavier atoms, such as Se, Te, and Po instead of S. Therefore, we investigated further heavy atom effects by our calculation method. The calculations predicted two orders larger k RISC of 1010 s-1 for the Se- and Te-containing molecules. Instead, the Po-containing molecule was predicted to show phosphorescence instead of TADF, suggesting that moderate heavy atom effect is favorable for TADF.Finally, we will present our recent study on inverted S1-T1 (iST) emitters. We have theoretically designed many iST candidates and predicted their photophysical properties. Some of them have been experimentally synthesized and measured their photophysical properties.We express sincere thanks to my group members. This work was supported by JSPS KAKENHI Grant Numbers JP20H05840 (Grant-in-Aid for Transformative Research Areas, “Dynamic Exciton”). The international Joint Usage/Research Centre at the Institute for Chemical Research, Kyoto University, Japan, supported computation time and NMR measurements.[1] H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Nature 492 (2012) 234.[2] H. Kaji, H. Suzuki, T. Fukushima, K. Shizu, K. Suzuki, S. Kubo, T. Komino, H. Oiwa, F. Suzuki, A. Wakamiya, Y. Murata, C. Adachi, Nat. Commun. 6 (2015) 8476.[3] Y. Wada, H. Nakagawa, S. Matsumoto, Y. Wakisaka, H. Kaji, Nat. Photon. 14 (2020) 643.[4] Y. Ren, Y. Wada, K. Suzuki, Y. Kusakabe, J. Geldsetzer, H. Kaji, Appl. Phys. Express 14 (2021) 071003.[5] Y. Wada, Y. Wakisaka, H. Kaji, ChemPhysChem 22 (2021) 625.[6] K. Shizu, H. Kaji, J. Phys. Chem. A 125 (2021) 9000.[7] K. Shizu, H. Kaji, Commun. Chem. 5 (2022) 53.[8] K. Shizu, Y. Ren, H. Kaji, ChemRxiv Doi: 10.26434/chemrxiv-2022-9drhb.

Optical conductivity and orbital magnetization of Floquet vortex states

Motivated by recent experimental demonstrations of Floquet topological insulators, there have been several theoretical proposals for using structured light, either spatial or spectral, to create other properties such as flat bands and vortex states. In particular, the generation of vortex states in a massive Dirac fermion insulator irradiated by light carrying nonzero orbital angular momentum (OAM) has been proposed. Here, we evaluate the orbital magnetization and optical conductivity as physical observables for such a system. We show that the OAM of light induces nonzero orbital magnetization and current density. The orbital magnetization density increases linearly as a function of the OAM degree. In certain regimes, we find that orbital magnetization density is independent of the system size, width, and Rabi frequency of light. It is shown that the orbital magnetization arising from our Floquet theory is large and can be probed by magnetometry measurements. Furthermore, we study the optical conductivity for various types of electron transitions between different states such as vortex, edge, and bulk that are present in the system. Based on the peaks in conductance, a scheme for the detection of vortex states is proposed.

Gamma-ray Induced Changes in the Optical Properties of Silver-polyaniline Nanocomposites

We prepared a nanocomposite (NC) containing polyaniline (PANI) and silver (Ag) nanoparticles (NPs). The aniline monomer was polymerized in the presence of Ag+ ions as an oxidizing agent. Samples from the prepared Ag-PANI NC film were irradiated with gamma rays (γ) radiation doses (5 − 60 kGy). The γ ray induced modifications in the prepared Ag-PANI NC optical properties are illustrated. The induced effect was explored using UV-vis spectroscopy and the International Commission on Illumination (CIE) color changes technique. A detailed study of the optical bandgap (Eg) was carried out. The results indicated that the direct Eg decreased from 2.41 to 1.94 eV with increasing γ irradiation. We attribute this decrease to the dominance of crosslinking that damaged the ordered structure and thus increased the amorphous regions. Furthermore, the study of Eg highlighted that the optical dielectric loss (ε”) parameter is a useful tool to specify the type of electronic transitions which was found to be a direct allowed transition for the Ag-PANI NC samples. Finally, the color changes between the pristine and irradiated samples were characterized. The pristine Ag-PANI film exhibited significant color changes during the irradiation.

The effect of annealing treatment on the structural and optical properties of nanostructured CuxO films obtained by 3D printing

This work studies the effect of post-growth annealing on the structural and optical properties of copper oxide films. Thin films were obtained by 3D printing on glass substrates using ink based on a suspension of CuO nanoparticles. To optimize their structural characteristics and optical quality, the samples were subjected to thermal annealing for 30 min in an argon environment at different temperatures from 250 °C to 500 °C. The obtained samples were studied by scanning electron microscopy, X-ray diffraction, energy dispersive X-Ray, Raman, optical and photoelectric spectroscopy. Based on the obtained results, the main structural and substructural characteristics of the films were established, such as lattice parameters, unit cell volume, texture, sizes of coherent scattering regions, and the level of microdeformation, as well as their dependence on the annealing temperature. In addition, the nature of optical absorption, band gap energies for various types of electronic transitions, and the optical quality of the studied nanostructured copper oxide films were determined. It was shown that CuO films annealed at 350 °C have the best crystalline and optical quality. It was established that at an annealing temperature above 400 °C, a phase transition from the tenorite phase to the cuprite phase is observed. At the same time, a change in the films' substructural characteristics is already observed at Ta = 400 °C. Optimal thermal annealing conditions of CuxO films for effective control of their phase composition have been established.

Covalent Triazine Framework C6N6 as an Electrochemical Sensor for Hydrogen-Containing Industrial Pollutants. A DFT Study

Industrial pollutants pose a serious threat to ecosystems. Hence, there is a need to search for new efficient sensor materials for the detection of pollutants. In the current study, we explored the electrochemical sensing potential of a C6N6 sheet for H-containing industrial pollutants (HCN, H2S, NH3 and PH3) through DFT simulations. The adsorption of industrial pollutants over C6N6 occurs through physisorption, with adsorption energies ranging from -9.36 kcal/mol to -16.46 kcal/mol. The non-covalent interactions of analyte@C6N6 complexes are quantified by symmetry adapted perturbation theory (SAPT0), quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) analyses. SAPT0 analyses show that electrostatic and dispersion forces play a dominant role in the stabilization of analytes over C6N6 sheets. Similarly, NCI and QTAIM analyses also verified the results of SAPT0 and interaction energy analyses. The electronic properties of analyte@C6N6 complexes are investigated by electron density difference (EDD), natural bond orbital analyses (NBO) and frontier molecular orbital analyses (FMO). Charge is transferred from the C6N6 sheet to HCN, H2S, NH3 and PH3. The highest exchange of charge is noted for H2S (-0.026 e-). The results of FMO analyses show that the interaction of all analytes results in changes in the EH-L gap of the C6N6 sheet. However, the highest decrease in the EH-L gap (2.58 eV) is observed for the NH3@C6N6 complex among all studied analyte@C6N6 complexes. The orbital density pattern shows that the HOMO density is completely concentrated on NH3, while the LUMO density is centred on the C6N6 surface. Such a type of electronic transition results in a significant change in the EH-L gap. Thus, it is concluded that C6N6 is highly selective towards NH3 compared to the other studied analytes.

Investigation of Structural and Optical Characteristics of Biopolymer Composites Based on Polyvinyl Alcohol Inserted with PbS Nanoparticles

The film casting method is implemented to synthesize a series of films consisting of polyvinyl alcohol (PVA) films and 4 wt%, 8 wt%, and 12 wt% lead sulfide (PbS) nanoparticles (NPs). X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Ultraviolet-visible (UV-vis) spectroscopy were used to ensure the impact of PbS loading on PVA properties, particularly optical ones. The FTIR results show a decrease in the intensity for all the bands and the XRD results show different features for the composites from that of the pure PVA. The optical properties, including optical transmission, surface reflection, and absorption, were investigated. Additionally, the significant optical parameters, for instance, the dielectric nature and refractive index of the films, were analyzed. The findings have shown that PbS NPs in the PVA films decrease UV and visible transmission through polymer composites and increase their ability to reflect the incident light. Tauc’s equation is applied to determine the optical bandgap energy (Eg) and verify whether it is direct or indirect. Using the relation between photon energy and optical dielectric loss, the Eg was measured and the type of electron transition was measured, which eases the exponent value (𝜸) specification from Tauc’s method. The Eg decreases from 6.3 eV to 5.25 eV when PbS NPs are added. The refractive index is improved from 1.27 to 2.16 for the polymer nanocomposite (NCPs) film with optimum PbS NPs. Then, the Wemple–DiDomenico model corresponding to a single oscillator is applied to the dispersive medium to determine the refractive index dispersion. Both the dispersive energy (Ed) and single-oscillator energy (Eo) are evaluated accurately. Moreover, the variation of both real and imaginary parts of the dielectric constant of polymer films were studied. Finally the optical parameters such as charge density, dielectric constant at high frequencies, optical mobility (µ), angular frequency (ωp), optical resistivity (ρ), and relaxation time (τ) of electrons are shown quantitatively. The ωp of the electron is increased from 1.06 × 1029 to 81.5 × 1029 Hz when the PbS NPs is added. The µ of the electrons is also increased from 4.85 to 6.22 cm2/(V·s) by adding the PbS NP.

Optical properties of multi-layers structured PEO/PVP solid polymer membranes doped with sodium perchlorate

In this present research work, fabrication of multi-layers structured (MLS) polymer membranes has been proposed to understand the variation of the optical bandgap and determine the types of electronic transitions as a function of sodium salt doping concentration. Solid MLS polymer membranes based on PEO/PVP have been prepared by the well-known solution cast technique. The recorded absorption, transmittance and reflectance spectra revealed that, incident energy absorption increased upon increase of salt dopant concentration and a shift of absorption edge towards lower energy region suggests the good complexation between the host polymers and dissociated salt (Na+, ClO4-) ions, which in turn the energy bandgap decrement expected. A detailed investigation has been carried out on the variation of refractive index of all the MLS polymer membranes as a function of salt doping concentration. The miscibility between the sodium salt and the individual polymers present in MLS polymer membranes can be understood from the linear relationship between the refractive index and the volume fraction of the added salt. The increase of extinction coefficient at high wavelengths was observed. The optical band gap measured from the plots of (αhυ)x versus photon energy (hυ) was compared to that determined from the optical dielectric loss.

Blending of Poly(methyl methacrylate) with Poly(1,3-diphenyl-1H-pyrazol-5-yl methacrylate): Investigation of its Optical Properties

In present study, a new blend polymer consisting of a pyrazole-derived polymer poly(1,3-diphenyl-1H-pyrazol-5-yl methacrylate) and poly(methyl methacrylate) was prepared solution mixing method. The blend polymer was spectrally characterized with FTIR and 1H-NMR techniques. TGA analysis showed that the blend polymer was stable up to 275.4 °C. A thin film of blend polymer was prepared by using spin coating technique. The UV measurements were obtained as a function of wavelength (300 – 700 nm). The optical and dispersion parameters were reported in detail. Transmittance was increased depending on the increasing wavelength whereas the reflectance decreased. The Transmittance value at 700 nm was measured as 97.55%, meaning the blend polymer was transparent. The refractive index at 700 nm was 1.37. The Urbach energy (Eu) and the optical band gap constant (Eg) were calculated to be 0.831 eV and 3.737 eV, respectively. The type of electronic transitions for polymer was determined as indirect allowed transition.

Structural and Optical Properties of Nanocrystalline 3-(2-Benzothiazolyl)-7-(diethylamino) Coumarin (C6) Thin Films for Optoelectronic Application

In the current work, the structural and optical properties of thermally evaporated 3-(2-Benzothiazolyl)-7-(diethylamino) coumarin [Coumarin 6 (C6)] thin films on a pre-cleaned quartz substrate were studied as a function of the annealing temperature. The influence of annealing on the structural, morphological, and molecular structures was investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy, respectively. The XRD and AFM results confirmed that the as-deposited and annealed films have nanostructural features (30.96–45.34 nm). Also, the increase in roughness of the C6 thin film surface resulted from particle agglomeration and coalescence. Optical constants of C6 thin films were derived from the transmittance T(λ) and reflectance, R(λ) measurements in the spectral range of 200–2500 nm. Analysis of the optical absorption coefficient data indicates that the type of electronic transition in these films is an indirect allowed transition. The estimated optical band gap was decreased from 2.12 eV to 2.01 eV as the annealing temperature was increased. Dispersion and dielectric parameters were determined as functions of the annealing temperature. Lastly, nonlinear optical parameters such as the third-order nonlinear susceptibility, χ(3) and nonlinear refractive index, n(2) were estimated and influenced by annealing temperature. The optical properties of C6 thin films were showed that C6 thin films would be used in a wide range of photonic applicationsGraphical

(Invited) Detailed Analysis of Highly-Efficient Emission in Organic Light-Emitting Diodes: The Dynamic Exciton Effect

Thermally activated delayed fluorescence (TADF) is an excellent way to convert originally dark triplet excitons into light.1 To realize the conversion, minimization of the energy gap between S1 and T1, called ΔE ST, has been effective.1,2 Actually, reverse intersystem crossing (RISC) becomes possible by the small ΔE ST.1-4 However, the rate constant of RISC (k RISC) is relatively small compared to those of competing processes, such as radiative and non-radiative decays, resulting that RISC is the rate-limiting process in TADF systems. Therefore, the acceleration of RISC is a key factor to obtain further excellent TADF-based organic light-emitting diodes (OLEDs).The small k RISC originates from small spin-orbit coupling (SOC). The S1 and T1 of TADF molecules tend to have charge transfer (CT) character, because the HOMO and LUMO are well-separated to make the ΔE ST small. The intersystem crossing (ISC) and RISC between CT-type S1 (1CT) and CT-type T1 (3CT) are spin-forbidden.5 This problem can be solved by intervening locally excited (LE) state(s) between 1CT and 3CT. Recently, we successfully achieved very fast RISC with a k RISC exceeding 107 s-1 by a new material design concept, named “tilted face-to-face alignment with optimal distance” (tFFO)6-8 by realizing the excellent energy level matching of 1CT, 3CT, and 3LE with sufficient SOC between 1CT and 3LE.In the presentation, I will first talk about detailed analysis of a TADF molecule, MA-TA.8-10 The performance is very high; the experimentally-obtained photoluminescence quantum yield (PLQY) and maximum external quantum efficiency (EQE) were 100% and 23.9%, respectively. The results seem to be contradictory to the above, because donor and acceptor (D-A) segments are perpendicular with each other resulting that both the S1 and T1 are CT-type, and higher-lying 3LE states cannot participate in the RISC process. Also, highly PLQY of 100% cannot be expected from the perpendicular structure. Our detailed quantum chemical analysis revealed that the dynamic or static D-A fluctuation was the key trigger of both the fast RISC and high PLQY. Such direct 3CT→1CT RISC-based OLEDs without using any 3LEs have an advantage that various kinds of hosts having different polarities can be used without sacrificing the device performance, that is, high EQE and blue-shifted emission can be realized simultaneously.Secondly, I will talk about the development of a high-throughput material screening method by quantitatively predicting rate constants of all relevant electronic transitions. TADF molecules have been designed through the calculations of ΔE ST and oscillator strength to realize effective RISC and following radiative decay simultaneously. However, in addition to ΔE ST, SOC is also another key factor to control k RISC as described above. Not only radiative but also non-radiative decays should be considered to obtain high PLQYs. We here propose a new method to predict TADF performance more precisely.11 Our method based on the Fermi golden rule enables us to theoretically predict relevant rate constants for all types of electronic transitions in an emitter molecule with reasonable computational cost. We applied the method to benzophenone; the calculated rate constants quantitatively agreed with the experimental ones. We are now extending this method to various TADF molecules and singlet fission systems.12-14 We express sincere thanks to my group members. This work was supported by JSPS KAKENHI Grant Numbers JP20H05840 (Grant-in-Aid for Transformative Research Areas, “Dynamic Exciton”). Computation time and NMR measurements were supported by the international Joint Usage/Research Centre at the Institute for Chemical Research, Kyoto University, Japan.1 H. Uoyama, K. Goushi, K. Shizu, H. Nomura & C. Adachi Nature 492, 234 (2012).2 H. Kaji et al. Nat. Commun. 6, 8476 (2015).3 Z. Yang et al. Chem. Soc. Rev. 46, 915 (2017).4 M. Y. Wong & E. Zysman-Colman Adv. Mater. 29, 1605444 (2017).5 M. A. El-Sayed J. Chem. Phys. 38, 2834 (1963).6 Y. Wada, H. Nakagawa, S. Matsumoto, Y. Wakisaka & H. Kaji Nat. Photon. 14, 643 (2020).7 Y. Kusakabe, Y. Wada, H. Nakagawa, K. Shizu & H. Kaji Front. Chem. 8, 530 (2020).8 H. Imahori, Y. Kobori & H. Kaji Acc. Chem. Res. 2, 501 (2021).9 Y. Wada, Y. Wakisaka & H. Kaji ChemPhysChem 22, 625 (2021).10 Y. Wada, K. Shizu & H. Kaji J. Phys. Chem. A 125, 4534 (2021).11 K. Shizu & H. Kaji J. Phys. Chem. A 125, 9000 (2021).12 K. Shizu, C. Adachi & H. Kaji J. Phys. Chem. A 124, 3641 (2020).13 K. Shizu, C. Adachi & H. Kaji Bull. Chem. Soc. Jpn. 93, 1305 (2020).14 K. Shizu, C. Adachi & H. Kaji ACS Omega 6, 2638 (2021).

Intensity of cooperative vibronic transitions in the Eu(III), Gd(III) and Tb(III) formates spectra.

The luminescence and absorption spectra of the lanthanide ions in solids and coordination compounds are characterized by sharp pure electronic lines, which are accompanied by much weaker lines of vibronic transitions. The vibronic spectroscopy is a good probing tool for investigations of the properties of surrounding ion ligands. The lanthanides formates are efficient luminescent crystals and can be viewed as the elementary type in the whole class of the oxygen-containing lanthanide coordination compounds. The intensity of vibronic transitions in spectra of luminescence and excitation europium (5 D0 →7 F2 , 7 F0 →5 D2 ), terbium (7 F6 →5 D4 ), gadolinium (6 P7/2 →8 S7/2 ) in anhydrous formates of the type Ln(HCOO)3 (Ln = Eu, Tb, Gd) and Y(HCOO)3 .2H2 O doped with Eu3+ and Tb3+ (C ~1 mol%) are reported. Also, the infrared and Raman spectra were obtained for the same compounds. Related integral intensity vibronic sidebands depend on the type of electronic transition of the same ion and varies for the same electronic transitions in different crystals. The obtained experimental data referring to the rate constants of vibronic transitions and intensity distribution in vibronic spectra on normal vibrations of the formate groups are in agreement with the predictions based on the Stavola-Dexter theory of cooperative vibronic transitions.

Transferring the wide band gap chitosan: POZ-based polymer blends to small optical energy band gap polymer composites through the inclusion of green synthesized Zn2+-PPL metal complex

In this study, the solution of black tea leaves (BTL) was extracted and used as a green coordination approach to synthesize Zinc metal ions (Zn2+)- polyphenol (PPL) complexes (Zn2+-PPL complexes) with increased UV–vis absorption. The FTIR of the BTL and Zn2+-PPL complex confirms the formation of the Zn2+-PPL complex through the wide variation in the intensity of FTIR bands. XRD shows that the interaction between Zn2+ ions and PPL produced an amorphous Zn2+-PPL complex. The prepared Zn2+-PPL complex with chitosan: Poly(2-ethyl-2-oxazoline) (CS: POZ) polymer blends exhibit enhanced optical properties. The polymer composite (PC) films are synthesized using the solution casting process. FTIR, XRD, and UV–vis spectroscopy techniques approve the synthesis of PCs films with handled optical properties. The structural properties of CS: POZ: Zn2+-PPL complex composite films confirm the amorphous phase dominant. The optical properties of CS: POZ blend and CS: POZ: Zn2+-PPL complex films are determined using UV–Visible spectroscopy, including refractive index (n), absorption edge, dielectric loss (εi), dielectric constant (εr), and bandgap energy (Eg). The Eg is measured by examining the εi optical parameter, whereas the types of electronic transition in the films are detected using Tauc's technique. Significant optical parameters such as localized charge density (N/m*), high-frequency dielectric constant (ε∞), relaxation time (τ), optical mobility (μopt), optical resistivity (ρopt), and plasma angular frequency (ωp) of electrons are measured. The N/m* values are increased from 7.3 × 1055m3/kg to 35.3 × 1055m3/kg by adding Zn2+-complex concentration, resulting in a significant reduction (4.8 eV to 1.6 eV) in the Eg. The Wemple–DiDomenico single oscillator model was used to measure the oscillator dispersion energy (Ed) and average oscillator energy (Eo) property.

Synergizing n → π* electronic transition and plasmonic hot electron injection enhances carrier generation of S-doped carbon nitride decorated with Au nanoparticles for Cr(VI) degradation

Promoting carrier separation has received much attention owing to attractive enhancement effects in improving the utilization efficiency of photo-generated carrier. However, the photocatalytic performance has remained limiting mainly due to lack of magnifying carrier generation fundamentally. Herein, carrier generation enhanced CNS0.6/Au-1 is established by loading ultrafine Au nanoparticles on S-doped carbon nitride (CNSx) for efficient hexavalent chromium degradation. CNSx can activate the n → π* electronic transition of carbon nitride besides keeping the original π → π* electronic transition. Plasmon-induced hot electron of Au nanoparticles merge with e− excited from π → π* and n → π* transition in CNSx increasing the amount of catalytically effective electrons, and the efficient carrier separation is also achieved. Near-infrared absorption CNS0.6/Au-1 exhibits a remarkable photo-reactivity for the degradation of Cr(Ⅵ), which can degrade 10 ppm Cr(Ⅵ) completely within 40 min. This work proposes a general strategy of increasing different types of electron transitions to promote carrier generation.

Low cost novel PEO based nano-composite for semiconductor and He–Ne lasers beam attenuation: Structural and optical properties

This paper reports the synthesis of low cost polyethylene oxide (PEO) based polymer nanocomposites (PNCs) for laser beam attenuation. The experimental investigations revealed the novel optical properties and bandgap reduction of PEO upon insertion of the Pb3O4 nanofiller. The changes in structural and optical properties of the prepared PNCs were explored using the X-ray diffraction (XRD) method and the ultraviolet–visible (UV–Vis). A broad shift of absorption is evidenced upon the addition of Pb3O4 nanofiller. The optical parameter, including absorption coefficient (α), linear refractive index (n), and dielectric loss (εi), were calculated. The optical band gap reduced significantly from 5.4 eV (neat PEO) to 1.8 eV for PEO doped with 9% Pb3O4. The direct and indirect electronic transitions in pure PEO and PEO: Pb3O4 PNCs were determined based on Tauc's model. The type of electron transition is specified with the assistance of εi spectra. The nonlinear optical parameter, including first-order susceptibility (χ1), third-order susceptibility (χ³), and nonlinear refractive index (n2), were studied. In addition, Laser beam attenuation characteristics for prepared PNCs samples were investigated using both semiconductor laser and He–Ne laser. The PEO: Pb3O4 PNCs significantly attenuated the laser power for both laser systems.

Synthesis and photophysical behavior of fluorescent benzazole dyes and fluorescent microparticles: Their use as fingerprint developer

Novel benzazole derivatives were synthesized and their photophysical properties were determined experimentally in different types of solvents also by theoretical calculations using Density Functional Theory (DFT). The results of the theoretical computational studies were well consistent with those observed experimentally, evidencing the type of electronic transitions that occurs between the frontiers orbitals. All synthesized derivatives are highly fluorescent in the violet-green region (363–536 nm) under ultraviolet light of 365 nm with large Stokes shift due to excited state intramolecular proton transfer (ESIPT) mechanism. Furthermore, the thermogravimetric and differential thermogravimetric analysis showed their good thermal stability, with decomposition temperature up to 250 °C. The fluorescent benzazole derivative was successfully entrapped into starch-based microparticles and applied for visualization of latent fingerprints on different types of surfaces common to forensic cases (metal, plastic, paper, wood, and ceramic).