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The water trimer, as the smallest water cluster in which the three-body interactions can manifest, is arguably the most important hydrogen-bonded trimer. Accurate, fully coupled quantum treatment of its excited intermolecular vibrations has long been an elusive goal. Here, we present the methodology that for the first time allows rigorous twelve-dimensional (12D) quantum calculation of the intermolecular vibration-tunneling eigenstates of the water trimer, with the monomers treated as rigid. These 12D eigenstates are used to simulate the low-frequency absorption spectrum of the trimer for direct comparison with the measured far-infrared (FIR) spectrum of the water trimer in helium nanodroplets. The 12D calculations reveal weak coupling between the large-amplitude torsional and intermolecular stretching vibrations. The calculated torsional tunneling splittings are in excellent agreement with spectroscopic results. There are visible differences between the spectrum simulated using the 12D eigenstates and that based on our earlier 9D calculations where the stretching vibrations are not included. The peaks in the 12D spectrum are generally shifted to slightly lower energies relative to those in the 9D spectrum, as well as the measured FIR spectrum, and are often split by intermolecular stretch–bend Fermi resonances that the 9D treatment cannot capture. [ABSTRACT FROM AUTHOR]

Accurate rovibrational molecular models are employed to gain insight in high-resolution into the collective effects and intermolecular processes arising when molecules in the gas phase interact with a resonant infrared (IR) radiation mode. An efficient theoretical approach is detailed, and numerical results are presented for the HCl, H2O, and CH4 molecules confined in an IR cavity. It is shown that by employing a rotationally resolved model for the molecules, revealing the various cavity-mediated interactions between the field-free molecular eigenstates, it is possible to obtain a detailed understanding of the physical processes governing the energy level structure, absorption spectra, and dynamic behavior of the confined systems. Collective effects, arising due to the cavity-mediated interaction between molecules, are identified in energy level shifts, in intensity borrowing effects in the absorption spectra, and in the intermolecular energy transfer occurring during Hermitian or non-Hermitian time propagation. [ABSTRACT FROM AUTHOR]

The strong coupling between infrared photonic resonances and vibrational transitions of organic molecules is called vibrational strong coupling (VSC), which presents attractive prospects for modifying molecular chemical characteristics and behaviors. Currently, VSC studies suffer from limited bandwidth or enormous mode volumes. In addition, in certain instances, the absorption spectrum of VSC is weaker, thus impeding the effective monitoring of the VSC effect. Here, we theoretically study the VSC effect by embedding 5-nm-thick organic molecules into a graphene plasmon nanocavity (GPNC). Pronounced anti-crossing characteristics with Rabi splitting exceeding 80 cm−1 are disclosed from the spectra of the coupled molecular system, benefiting from the ultra-small mode volume provided by the GPNC. Further assembling the GPNC into a perfect absorber configuration can significantly enhance the spectral peaks of the VSC effect, thus maximizing the reachability of the VSC phenomenon. Furthermore, the tunability of graphene enables monitoring of spectral changes by electrically adjusting graphene's Fermi level in a structure with fixed geometric parameters. In addition, we establish an analytical framework in alignment with computational simulations to elucidate the triggering criteria for the VSC mode, thereby giving a clear picture for understanding the physical processes that form the VSC mode. Given that graphene supports plasmon modes across an extensive range extending from infrared to terahertz, the suggested GPNC presents a suitable framework for investigating the VSC effect of diverse organic materials. [ABSTRACT FROM AUTHOR]

We report improved thermoelectric (TE) properties of mesostructured silicon powder arrays simply prepared by die-pressing without sintering. In contrast to bromoethane's modest effect, the symmetric dibromoethane molecule coupling could significantly increase the conductivity of Si powder array TE device, from 12.7 S cm−1 of a silicon powder array to 62.3 S cm−1, which is possibly caused by the high electronic transmission probability of symmetric organic molecule–Si crystal coupling, and additionally enhanced by Si bandgap narrowing and defect states of an organic–inorganic interface identified by UV–vis absorption spectra and photoluminescence spectroscopy. Boosted by the very low thermal conductivity (0.58 W m−1 K−1), the dimensionless figure of merit, the ZT value of an Si powder array remotely doped by dibromoethane, ∼0.173, was obtained at 385 K, which is about 17 times higher than that of the bulk Si. An Si–organic hybrid TE device shows potentials to approach the threshold of practical applications with moderate ZT performance and low cost. [ABSTRACT FROM AUTHOR]

We have performed a series of broadband multidimensional electronic spectroscopy experiments to probe the electronic and vibrational dynamics of the canthaxanthin chromophore of the Orange Carotenoid Protein (OCP) from Synechocystis sp. PCC 6803 in its photoactivated red state, OCPR. Cross-peaks observed below the diagonal of the two-dimensional electronic spectrum indicate that absorption transitions prepare the bright S2 state of the ketocarotenoid canthaxanthin near to a sequence of conical intersections, allowing passage to the dark S1 state via the Sx intermediate in < 50 fs. Rapid damping of excited-state coherent wavepacket motions suggests that the branching coordinates of the conical intersections include out-of-plane deformation and C=C stretching coordinates of the π-conjugated isoprenoid backbone. The unusual proximity of the Franck–Condon S2 state structure to the conical intersections with Sx and S1 suggests that the protein surroundings of canthaxanthin prepare it to function as an excitation energy trap in the OCPR–phycobilisome complex. Numerical simulations using the multimode Brownian oscillator model demonstrate that the ground-state absorption spectrum of OCPR overlaps with the fluorescence emission spectrum of allophycocyanin due to spectral broadening derived especially from the intramolecular motions of the canthaxanthin chromophore in its binding site. [ABSTRACT FROM AUTHOR]

We recorded the hyper-Raman spectra resulting from the interaction of a near-infrared (near-IR) picosecond pulse and a terahertz (THz) ultrashort pulse at the surface of a (111) silicon sample. A simple model is proposed to analyze the evolution of the hyper-Raman spectra vs the time delay between the near-IR and THz pulses. It links the hyper-Raman spectra to the multi-phonon absorption in silicon. This approach makes it possible to demonstrate that, during carrier generation by the near-IR pulse, the two-phonon and three-phonon absorption bands are enhanced in modes involving optical phonons. This process results from the very rapid and strong population of the optical phonons induced by the photo-generated hot carriers. It occurs over a few hundreds of femtoseconds and lasts throughout the duration of the near-IR pulse. [ABSTRACT FROM AUTHOR]

Although recent advances in simulating open quantum systems have led to significant progress, the applicability of numerically exact methods is still restricted to rather small systems. Hence, more approximate methods remain relevant due to their computational efficiency, enabling simulations of larger systems over extended timescales. In this study, we present advances for one such method, namely, the numerical integration of Schrödinger equation (NISE). First, we introduce a modified ensemble-averaging procedure that improves the long-time behavior of the thermalized variant of the NISE scheme, termed thermalized NISE. Second, we demonstrate how to use the NISE in conjunction with (highly) structured spectral densities by utilizing a noise generating algorithm for arbitrary structured noise. This algorithm also serves as a tool for establishing best practices in determining spectral densities from excited state calculations along molecular dynamics or quantum mechanics/molecular mechanics trajectories. Finally, we assess the ability of the NISE approach to calculate absorption spectra and demonstrate the utility of the proposed modifications by determining population dynamics. [ABSTRACT FROM AUTHOR]

We present a detailed spectroscopic analysis of the first absorption band of the six possible conformers of 1,6-diphenyl-1,3,5-hexatriene, obtained by changing the configuration of trans double bonds to cis. To this end, we computed the absorption spectra using FCclasses 3.0 code. First, we assessed the performance of PBE0 and CAM-B3LYP density functional theory functionals with different basis sets to reproduce the experimental spectra. Additionally, we considered different models to compute the spectra. PBE0/def2tZVP with an adiabatic hessian model with internal coordinates yields results in very good agreement with experimental data. Subsequently, we analyzed the different contributions of vibronic transition to the spectral structure, correlating ground state conformation with spectral shape, and studied the effect of temperature on the absorption first band. [ABSTRACT FROM AUTHOR]

We have synthesized L-cysteine and oleylamine stabilized CsPbBr3 perovskite quantum dots (PQDs) and coupled them with gold nanoparticles (AuNPs). The PQDs and AuNPs, as well as their hybrid nanostructures (HNS), were characterized using UV–visible (UV–vis) and photoluminescence (PL) spectroscopy. The UV–vis spectra show absorption bands of the HNS at 503 and 520 nm, attributed mainly to PQDs and AuNPs, respectively. The PQDs show a strong excitonic PL band peaked at 513 nm from PQDs. The HR-TEM results show the formation of hybrid structures between PQDs and AuNPs, which is also supported by the PL quenching of the PQDs by the coupled AuNPs. Ultrafast dynamics of the exciton and charge carriers in the HNS and pristine PQD were studied using femtosecond transient absorption. Multiexponential fitting of the dynamic data revealed the existence of shallow and deep trap states in pristine PQDs and ultrafast electron transfer from PQDs to AuNPs in the HNS. A kinetic model was proposed to account for the key dynamic processes involved and to extract the time for electron transfer from PQDs to AuNPs in the HNS, found to be ∼2 ps. Dynamic processes in pristine PQDs are largely unchanged by HNS formation with AuNPs. [ABSTRACT FROM AUTHOR]

The high resolution Rydberg absorption spectrum of 2-butyne C4H6 recorded previously at the SOLEIL synchrotron facility has been interpreted using multichannel quantum defect theory (MQDT). The calculations are based on the continuum scattering calculations of Xu et al., J. Chem. Phys. 136, 154303 (2012) and of Jacovella et al., J. Phys. Chem. A 119, 12339 (2015) pertaining to the dipole-allowed excited state symmetries in absorption from the ground state. In contrast to the traditional approach of calculating low-lying electronic states first and then attempting to extend the calculations to ever higher energy, here the analysis proceeds through the extension of these detailed calculations of the electronic continuum scattering down into the discrete region of the spectrum. The continuum reaction matrices and dipole transition moments are adapted to the discrete Rydberg region via the use of an energy-modified formulation of MQDT theory and associated energy dependences of the quantum defects. The analysis reproduces more than 40 Rydberg states from n ≈ 10 down to the 3d and 4s levels with an rms error of better than 20 cm−1. These belong to five Rydberg series with three different molecular symmetries. While the approach predicts many additional series, most of these are calculated and observed to carry only little oscillator strength. The analysis shows that the Rydberg spectrum is dominated by the excitation of an e″ symmetry electron of fδ and gπ type, in line with what previous studies of the above-threshold shape resonance of 2-butyne have shown. The present study is intended to serve as an example showing how first principles continuum calculations may be useful for the interpretation of highly bound discrete states in a range that poses problems for the standard ab initio techniques. The quantitative treatment of the dipole absorption cross sections is deferred to a future paper. [ABSTRACT FROM AUTHOR]

The motional narrowing effect has been extensively studied for cavity exciton–polariton systems in recent decades both experimentally and theoretically, which is featured by (1) the subaverage behavior and (2) the asymmetric linewidths for the upper polariton and the lower polariton. However, a minimal theoretical model that is clear and adequate to address all these effects as well as the linewidth scaling relations remains missing. In this work, based on the single mode 1D Holstein–Tavis–Cummings (HTC) model, we studied the motional narrowing effect of the polariton linear absorption spectra via both semi-analytic derivations and numerically exact quantum dynamics simulations using the hierarchical equations of motion approach. The results reveal that under collective light–matter coupling between a cavity mode and N molecules, the polariton linewidth scales as 1 / N under the slow limit, while scales as 1/N under the fast limit, due to the polaron decoupling effect. Furthermore, by varying the detunings, the polariton linewidths exhibit significant motional narrowing, covering both characters mentioned above. Our analytic linewidth expressions [Eqs. (34) and (35)] agree well with the numerical exact simulations in all the parameter regimes we explored. These results indicate that the physics of motional narrowing is adequately accounted for by the single-mode 1D HTC model. We envision that both the numerical results and the analytic polariton linewidths expression presented in this work will offer great theoretical value for providing a better understanding of the exciton–polariton motional narrowing based on the HTC model. [ABSTRACT FROM AUTHOR]

Conducting a comprehensive molecular-level evaluation of a photoacid generator (PAG) and its subsequent impact on lithography performance can facilitate the rational design of a promising 193 nm photoresist tailored to specific requirements. In this study, we integrated spectroscopy and computational techniques to meticulously investigate the pivotal factors of three prototypical PAG anions, p-toluenesulfonate (pTS−), 2-(trifluoromethyl)benzene-1-sulfonate (TFMBS−), and triflate (TF−), in the lithography process. Our findings reveal a significant redshift in the absorption spectra caused by specific PAG anions, attributed to their involvement in electronic transition processes, thereby enhancing the transparency of the standard PAG cation, triphenylsulfonium (TPS+), particularly at ∼193 nm. Furthermore, the electronic stability of PAG anions can be enhanced by solvent effects with varying degrees of strength. We observed the lowest vertical detachment energy of 6.6 eV of pTS− in PGMEA solution based on the polarizable continuum model, which prevents anion loss at 193 nm lithography. In addition, our findings indicate gas-phase proton affinity values of 316.4 kcal/mol for pTS−, 308.1 kcal/mol for TFMBS−, and 303.2 kcal/mol for TF−, which suggest the increasing acidity strength, yet even the weakest acid pTS− is still stronger than strong acid HBr. The photolysis of TPS+-based PAG, TPS+·pTS−, generated an excited state leading to homolysis bond cleavage with the lowest reaction energy of 83 kcal/mol. Overall, the PAG anion pTS− displayed moderate acidity, possessed the lowest photolysis reaction energy, and demonstrated an appropriate redshift. These properties collectively render it a promising candidate for an effective acid producer. [ABSTRACT FROM AUTHOR]

A holistic computational analysis is developed to calculate the quantum efficiency of InAs/GaSb superlattice-based photodetectors. Starting with the electronic band characteristics computed by taking InSb/GaAs at the interface using the 8-band k. p approach, we demonstrate the impact of InAs and GaSb widths on the bandgap, carrier concentration, and the oscillator strength for type-II superlattice absorbers. Subsequently, the alteration of these characteristics due to the extra AlSb layer in the M superlattice absorber is investigated. Extending our models for determining TE- and TM-polarized optical absorption, our calculations reveal that the TE-polarized absorption shows a substantial influence near the conduction-heavy hole band transition energy, which eventually diminishes, owing to the dominant TM contribution due to the conduction-light hole band transition. Extending our analysis to the dark currents, we focus mainly on Schokley–Read–Hall recombination and radiative recombination at lower temperatures and show that Schokley–Read–Hall dominates at low-level injection. We show that short-wavelength and mid-wavelength M superlattice structures exhibit higher quantum efficiency than the corresponding same bandgap type-II superlattice with the lower diffusion dark current. Furthermore, we analyze the density of states blocked by the barrier, crucial for XBp photodetector after absorber examination. Our work, thus, sets a stage for a holistic and predictive theory aided analysis of the type-II superlattice absorbers, from the atomistic interfacial details all the way to the dark currents and absorption spectra. [ABSTRACT FROM AUTHOR]

We investigate the effects of solvents on the geometry, absorption spectrum, and first hyperpolarizability of six push–pull molecules, each containing a 4,5-dicyanoimidazole group as an electron acceptor and a N,N-dimethylamino group as an electron donor, with systematically extended π-conjugated systems. Geometry optimizations in dichloromethane, methanol, water, and formamide under normal thermodynamic conditions were performed using the average solvent electrostatic configuration–free energy gradient method, which employs a discrete solvent model. The conformational structure of molecules is moderately affected by the environment, with the π-conjugated system becoming more planar in protic solvents. Solvent effects on the first hyperpolarizability result in marked increases that are in line with the red shifts of the absorption spectrum. The hyperpolarizability of smaller molecules within the set may be significantly influenced by the effects of geometry relaxation in highly polar protic solvents. The results illustrate the role of hydrogen bonds in the structure and electronic properties of push–pull molecules in protic environments. For smaller molecules, hydrogen bonds significantly contribute to enhancing the hyperpolarizability, but the effect of these specific interactions becomes less significant with the length of the π-conjugated system. [ABSTRACT FROM AUTHOR]

In this work, we have implemented the time-dependent density functional theory approximate auxiliary s function (TDDFT-aas) method, which is an approximate TDDFT method. Instead of calculating the exact two-center electron integrals in the K coupling matrix when solving the Casida equation, we approximate the integrals, thereby reducing the computational cost. In contrast to the related TDDFT plus tight-binding (TDDFT+TB) method, a new type of gamma function is used in the coupling matrix that does not depend on the tight-binding parameters. The calculated absorption spectra of silver and gold nanoparticles using TDDFT-aas show good agreement with TDDFT and TDDFT+TB results. In addition, we have implemented the analytical excited-state gradients for the TDDFT-aas method, which makes it possible to calculate the emission energy of molecular systems. [ABSTRACT FROM AUTHOR]

The A ̃ 1A″ ← X ̃ 1A′ absorption spectra of HONO and DONO were simulated by a full six-dimensional quantum mechanical method based on the newly constructed potential energy surfaces for the ground and excited electronic states, which were represented by the neural network method utilizing over 36 000 ab initio energy points calculated at the multireference configuration interaction level with Davidson correction. The absorption spectrum of HONO/DONO comprises a superposition of the spectra from two isomers, namely, trans- and cis-HONO/DONO, due to their coexistence in the ground X ̃ 1A′ state. Our calculated spectra of both HONO and DONO were found to be in fairly good agreement with the experiment, including the energy positions and widths of the peaks. The dominant progression was assigned to the N=O stretch mode ( 2 0 n ) associated with trans-HONO/DONO, which can be attributed to the promotion of an electron to the π* orbital of N=O. Specifically, the resonances with higher vibrational quanta were found to be in the domain of the Feshbach-type resonances. The assignments of the spectra and mode specificity therein are discussed. [ABSTRACT FROM AUTHOR]

We describe a procedure for the calculation of quasi-diabatic states within the recently introduced DFT/MRCI(2) framework [S. P. Neville and M. S. Schuurman, J. Chem. Phys. 157, 164103 (2022)]. Based on an effective Hamiltonian formalism, the proposed procedure, which we term QD-DFT/MRCI(2), has the advantageous characteristics of being simultaneously highly efficient and effectively black box in nature while directly yielding both quasi-diabatic potentials and wave functions of high quality. The accuracy and efficiency of the QD-DFT/MRCI(2) formalism are demonstrated via the simulation of the vibronic absorption spectra of furan and chlorophyll a. [ABSTRACT FROM AUTHOR]

Algebraic diagrammatic construction (ADC) is a computationally efficient approach for simulating excited electronic states, absorption spectra, and electron correlation. Due to their origin in perturbation theory, the single-reference ADC methods may be susceptible to spin contamination when applied to molecules with unpaired electrons. In this work, we develop an approach to quantify spin contamination in the ADC calculations of electronic excitations and apply it to a variety of open-shell molecules starting with either the unrestricted (UHF) or restricted open-shell (ROHF) Hartree–Fock reference wavefunctions. Our results show that the accuracy of low-order ADC approximations [ADC(2) and ADC(3)] significantly decreases when the UHF reference spin contamination exceeds 0.05 a.u. Such strongly spin-contaminated molecules exhibit severe excited-state spin symmetry breaking that contributes to decreasing the quality of computed excitation energies and oscillator strengths. In a case study of phenyl radical, we demonstrate that spin contamination can significantly affect the simulated UV/Vis spectra, altering the relative energies, intensities, and order of electronic transitions. The results presented here motivate the development of spin-adapted ADC methods for open-shell molecules. [ABSTRACT FROM AUTHOR]

Proflavine, a fluorescent cationic dye with strong absorption in the visible, has been proposed as a potential contributor to diffuse interstellar bands (DIBs). To investigate this hypothesis, it is essential to examine the spectra of cold and isolated ions for comparison. Here, we report absorption spectra of proflavine ions, trapped in a liquid-nitrogen-cooled ion trap filled with helium-buffer gas, as well as fluorescence spectra to provide further information on the intrinsic photophysics. We find absorption- and fluorescence-band maxima at 434.2 ± 0.1 and 434.7 ± 0.3 nm, corresponding to a Stokes shift of maximum 48 cm−1, which indicates minor differences between ground-state and excited-state geometries. Based on time-dependent density functional theory, we assign the emitting state to S2 as its geometry closely resembles that of S0, whereas the S1 geometry differs from that of S0. As a result, simulated spectra involving S1 exhibit long Franck-Condon progressions, absent in the experimental spectra. The latter displays well-resolved vibrational features, assigned to transitions involving in-plane vibrational modes where the vibrational quantum number changes by one. Dominant transitions are associated with vibrations localized on the NH2 moieties. Experiments repeated at room temperature yield broader spectra with maxima at 435.5 ± 1 nm (absorption) and 438.0 ± 1 nm (fluorescence). We again conclude that prevalent fluorescence arises from S2, i.e., anti-Kasha behavior, in agreement with previous work. Excited-state lifetimes are 5 ± 1 ns, independent of temperature. Importantly, we exclude the possibility that a narrow DIB at 436.4 nm originates from cold proflavine cations as the band is redshifted compared to our absorption spectra. [ABSTRACT FROM AUTHOR]

In recent years, all-inorganic perovskite materials have become an ideal choice for new thin film solar cells due to their excellent photophysical properties and have become a research hotspot. Studying the ultrafast dynamics of photo-generated carriers is of great significance for further improving the performance of such devices. In this work, we focus on the transient dynamic process of CsPbBr3/TiO2 composite systems with different Mn2+ doping contents using femtosecond transient absorption spectroscopy technology. We used singular value decomposition and global fitting to analyze the transient absorption spectra and obtained three components, which are classified as hot carrier cooling, charge transfer, and charge recombination processes, respectively. We found that the doping concentration of Mn2+ has an impact on all three processes. We think that the following two factors are responsible: one is the density of defect states and the other is the bandgap width of perovskite. As the concentration of doped Mn2+ increases, the charge transfer time constant shows a trend of initially increasing, followed by a subsequent decrease, reaching a turning point. This indicates that an appropriate amount of Mn2+ doping can effectively improve the photoelectric performance of solar cell systems. We proposed a possible charge transfer mechanism model and further elucidated the microscopic mechanism of the effect of Mn2+ doping on the interface charge transfer process of the CsPbBr3/TiO2 solar cell system. [ABSTRACT FROM AUTHOR]

The plasmonic coupling between silver (Ag) and gold (Au) nanoparticles (NPs) under four polarization modes was examined: a longitudinal mode (L-mode), where the electric field of a linearly polarized incident light parallels the dimer axis, and three transverse modes (T-modes), where the electric field of the light is perpendicular to the dimer axis. The coupling was studied using the discrete dipole approximation followed by an in-house postprocessing code that determines the extinction (Qext), absorption (Qabs), and near-field (Qnf) spectra from the individual NPs as well as the whole system. In agreement with the literature results, the extinction/absorption spectra of the whole dimer have two peaks, one near the Ag localized surface plasmon resonance (LSPR) region and the other at the Au LSPR region, with the peak at Ag LSPR being reduced in all modes and the peak at Au LSPR being red-shifted and increased in the L-mode but not in the T-modes. It is further shown that the scattering at the Ag LSPR region is reduced and becomes less than the isolated Ag NPs, but the absorption at the Ag LSPR is increased and becomes greater than the isolated Ag NPs for the 50 nm Ag–Au heterodimer. This suggests that the scattering from Ag NPs is being reabsorbed by the neighboring Au NPs due to the interband electronic transition in Au at that wavelength range. The Qext from the individual NP in the heterodimer shows the presence of the Fano profile on the Au NP but not on the Ag NP. This phenomenon was further investigated by using a dielectric particle (DP) placed near the Ag or Au NPs. The Fano profile appears in the absorbing DP spectra placed near either Ag or Au NPs. However, the Fano profile is masked upon further increases in the refractive index value of the DP particle. This explains the absence of a Fano profile on the Ag NPs in the Ag–Au heterodimer. The large near-field enhancement on both Ag and Au NPs at the Au plasmonic wavelength in the L-mode for large NPs was investigated through a DP-Au system. The large enhancement was shown to arise from a large imaginary component of the DP refractive index and a small real component. Through examination of both the near- and far-field properties of the individual NPs as well as the whole system and examinations of DP-Ag and DP-Au systems, our study provides a new understanding of the couplings between Ag and Au NPs. [ABSTRACT FROM AUTHOR]

We study the accuracy of excited state (ES) geometries using optimally tuned LC-PBE functionals with tuning based on GW quasiparticle energies. We compare the results obtained with the PBE, PBE0, non-tuned, and tuned LC-PBE functionals with available high-level CC reference values as well as experimental data. First, we compare ES geometrical parameters obtained for three different types of systems: molecules composed of a few atoms, 4-(dimethylamino)benzonitrile (DMABN), and conjugated dyes. To this end, we used wave-function results as benchmarks. Next, we evaluate the accuracy of the theoretically simulated spectra as compared to the experimental ones for five large dyes. Our results show that, besides small compact molecules for which tuning LC-PBE does not allow obtaining geometries more accurate than those computed with standard functionals, tuned range-separated functionals are clearly to be favored, not only for ES geometries but also for 0–0 energies, band shapes, and intensities for absorption and emission spectra. In particular, the results indicate that GW-tuned LC-PBE functionals provide improved matching with experimental spectra as compared to conventionally tuned functionals. It is an open question whether TD-DFT with GW-tuned functionals can qualitatively mimic the actual many-body Bethe–Salpeter (BSE/GW) formalism for which analytic ionic gradients remain to be developed. [ABSTRACT FROM AUTHOR]

A high-resolution absorption spectrum of the S1–S0 transition of free-base phthalocyanine was observed and analyzed with improved reliability. The spectrum, with a partially resolved rotational structure, was obtained by using the buffer-gas cooling technique and a single-mode tunable laser. Our new analysis reveals that the S 1 ← S 0 0 0 0 band belongs to the a-type transition, where the electronic transition moment aligns parallel to the NH–HN direction, allowing the assignment of the S1 state to 1B3u. These results agree with a prior study using supersonic expansion and are well supported by theoretical calculations. Interestingly, the rotational constant B in the S1 state, which is often smaller than that in the ground state for typical molecules, was found to be slightly larger than that in the S01Ag state. This suggests a change in the character of π bonds with the electronic excitation. [ABSTRACT FROM AUTHOR]

Semiconducting MXenes are an intriguing two-dimensional (2D) material class with promising electronic and optoelectronic properties. Here, we focused on recently prepared Hf-based MXenes, namely, Hf3C2O2 and Hf2CO2. Using the first-principles calculation and excited state corrections, we proved their dynamical stability, reconciled their semiconducting behavior, and obtained fundamental gaps by using the many-body GW method (indirect 1.1 and 2.2 eV; direct 1.4 and 3.5 eV). Using the Bethe–Salpeter equation, we subsequently provided optical gaps (0.9 and 2.7 eV, respectively), exciton binding energies, absorption spectra, and other properties of excitons in both Hf-based MXenes. The indirect character of both 2D materials further allowed for a significant decrease of excitation energies by considering indirect excitons with exciton momentum along the Γ-M path in the Brillouin zone. The first bright excitons are strongly delocalized in real space while contributed by only a limited number of electron–hole pairs around the M point in the k-space from the valence and conduction band. A diverse range of excitonic states in Hf3C2O2 MXene lead to a 4% and 13% absorptance for the first and second peaks in the infrared region of absorption spectra, respectively. In contrast, a prominent 28% absorptance peak in the visible region appears in Hf2CO2 MXene. Results from radiative lifetime calculations indicate the promising potential of these materials in optoelectric devices requiring sustained and efficient exciton behavior. [ABSTRACT FROM AUTHOR]

A time-dependent vibrational electronic coupled-cluster (VECC) approach is proposed to simulate photo-electron/UV-VIS absorption spectra as well as time-dependent properties for non-adiabatic vibronic models, going beyond the Born–Oppenheimer approximation. A detailed derivation of the equations of motion and a motivation for the ansatz are presented. The VECC method employs second-quantized bosonic construction operators and a mixed linear and exponential ansatz to form a compact representation of the time-dependent wave-function. Importantly, the method does not require a basis set, has only a few user-defined inputs, and has a classical (polynomial) scaling with respect to the number of degrees of freedom (of the vibronic model), resulting in a favorable computational cost. In benchmark applications to small models and molecules, the VECC method provides accurate results compared to multi-configurational time-dependent Hartree calculations when predicting short-time dynamical properties (i.e., photo-electron/UV–VIS absorption spectra) for non-adiabatic vibronic models. To illustrate the capabilities, the VECC method is also successfully applied to a large vibronic model for hexahelicene with 14 electronic states and 63 normal modes, developed in the group by Aranda and Santoro [J. Chem. Theory Comput. 17, 1691, (2021)]. [ABSTRACT FROM AUTHOR]

Two new supramolecular photocatalysts made of covalently linked Ru(II) polypyridine chromophore subunits ([Ru(bpy)3]2+-type species; bpy = 2,2′-bipyridine) and [RuL(pic)2] (L = 2,2′-bipyridine-6,6′-dicarboxylic acid; pic = 4-picoline) water oxidation catalyst subunits have been prepared. The new species, 1 and 2, contain chromophore and catalyst subunits in the molecular ratios 1:1 and 1:2, respectively. The model chromophore species [Ru(bpy)2(L1)]2+ (RuP1; L1=4-[2-(4-pyridyl)-2-hydroxyethyl]-4-methyl-2,2′-bipyridine) and [Ru(bpy)2(L2)]2+ (RuP2; L2 = 4,4′-bis[2-(4-pyridyl)-2-hydroxyethyl]-2,2′-bipyridine) have also been prepared. The absorption spectra, oxidation behavior, and luminescent properties of 1 and 2 have been studied, and the results indicate that each subunit largely maintains its own properties in the supramolecular species. However, the luminescence of the chromophore subunits is significantly quenched in 1 and 2 in comparison with the luminescence of the respective model species. Both 1 and 2 exhibit catalytic water oxidation in the presence of cerium ammonium nitrate, exhibiting an I2M mechanism, with a better efficiency than the known catalyst [RuL(pic)2] under the same experimental conditions. Upon light irradiation, in the presence of persulfate as a sacrificial acceptor agent, 1 and 2 are more efficient photocatalysts than a system made of separated [Ru(bpy)3]2+ and [RuL(pic)2] species, highlighting the advantage of using multicomponent, supramolecular species with respect to isolated species. The O–O bond formation step is I2M, even in the photo-driven process. The photocatalytic process of 2 is more efficient than that of 1, with the turnover frequency reaching a value of 1.2 s−1. A possible reason could be an increased local concentration of catalytic subunits in the needed bimolecular assembly required for the I2M mechanism in 2 with respect to 1, a consequence of the presence of two catalytic subunits in each multicomponent species 2. [ABSTRACT FROM AUTHOR]

By employing the numerically accurate multiple Davydov Ansatz (mDA) formalism in combination with the thermo-field dynamics (TFD) representation of quantum mechanics, we systematically explore the influence of three parameters—temperature, photonic-mode detuning, and qubit–phonon coupling—on population dynamics and absorption spectra of the Holstein–Tavis–Cummings (HTC) model. It is found that elevated qubit–phonon couplings and/or temperatures have a similar impact on all dynamic observables: they suppress the amplitudes of Rabi oscillations in photonic populations as well as broaden the peaks and decrease their intensities in the absorption spectra. Our results unequivocally demonstrate that the HTC dynamics is very sensitive to the concerted variation of the three aforementioned parameters, and this finding can be used for fine-tuning polaritonic transport. The developed mDA-TFD methodology can be efficiently applied for modeling, predicting, optimizing, and comprehensively understanding dynamic and spectroscopic responses of actual molecular systems in microcavities. [ABSTRACT FROM AUTHOR]

We present a detailed theoretical analysis of polarized absorption spectra and linear dichroism of cyanine dye aggregates whose unit cells contain two molecules. The studied threadlike ordered system with a molecular exciton delocalized along its axis can be treated as two chains of conventional molecular aggregates, rotated relative to each other at a certain angle around the aggregate axis. Our approach is based on the general formulas for the effective cross section of light absorption by a molecular aggregate and key points of the molecular exciton theory. We have developed a self-consistent theory for describing the orientational effects in the absorption and dichroic spectra of such supramolecular structures with nonplanar unit cell. It is shown that the spectral behavior of such systems exhibits considerable distinctions from that of conventional cyanine dye aggregates. They consist in the strong dependence of the relative intensities of the J- and H-type spectral bands of the aggregate with a nonplanar unit cell on the angles determining the mutual orientations of the transition dipole moments of constituting molecules and the aggregate axis as well as on the polarization direction of incident light. The derived formulas are reduced to the well-known analytical expressions in the particular case of aggregates with one molecule in the unit cell. The calculations performed within the framework of our excitonic theory combined with available vibronic theory allow us to quite reasonably explain the experimental data for the pseudoisocyanine bromide dye aggregate. [ABSTRACT FROM AUTHOR]

In this work, charge photogeneration and recombination processes of PM6:IDIC-4F and PM6:IDIC blend films were investigated by the steady-state and time-resolved spectroscopies, as well as the time-dependent density functional theory calculations. The peaks in absorption and photoluminescence (PL) spectra of IDIC and IDIC-4F solutions were assigned by combining the experiment and the simulation of UV–vis absorption and PL spectra. For neat acceptor films, the exciton diffusion length of neat IDIC and IDIC-4F films was estimated as ∼28.9 and ∼19.9 nm, respectively. For PM6-based blend films, we find that the fluorine substitution engineering on the IDIC acceptor material can increase the phase separate size of acceptor material in blend films, resulting in the reduction of dissociation efficiencies of acceptor excitons. In addition, we find that the charge recombination in PM6:IDIC-4F is dominated by bimolecular recombination, in comparison to geminate type carrier recombination in PM6:IDIC blend films. In addition, we find that thermal annealing treatment has a weak influence on carrier recombination but slightly reduces the exciton dissociation efficiency of acceptor in PM6:IDIC blend films, leading to a slightly reduced power conversion efficiency of PM6:IDIC solar cells. These results may shed light on the design of high-performance semiconductor molecules for application in solar cells. [ABSTRACT FROM AUTHOR]

The second order cumulant method offers a promising pathway to predicting optical properties in condensed phase systems. It allows for the computation of linear absorption spectra from excitation energy fluctuations sampled along molecular dynamics (MD) trajectories, fully accounting for vibronic effects, direct solute–solvent interactions, and environmental polarization effects. However, the second order cumulant approximation only guarantees accurate line shapes for energy gap fluctuations obeying Gaussian statistics. A third order correction has recently been derived but often yields unphysical spectra or divergent line shapes for moderately non-Gaussian fluctuations due to the neglect of higher order terms in the cumulant expansion. In this work, we develop a corrected cumulant approach, where the collective effect of neglected higher order contributions is approximately accounted for through a dampening factor applied to the third order cumulant term. We show that this dampening factor can be expressed as a function of the skewness and kurtosis of energy gap fluctuations and can be parameterized from a large set of randomly sampled model Hamiltonians for which exact spectral line shapes are known. This approach is shown to systematically remove unphysical contributions in the form of negative absorbances from cumulant spectra in both model Hamiltonians and condensed phase systems sampled from MD and dramatically improves over the second order cumulant method in describing systems exhibiting Duschinsky mode mixing effects. We successfully apply the approach to the coumarin-153 dye in toluene, obtaining excellent agreement with experiment. [ABSTRACT FROM AUTHOR]

A synchrotron based vacuum ultraviolet absorption spectrum for γ-pyrone has been interpreted in terms of singlet excited electronic states using a variety of coupled cluster, configuration interaction, and density functional calculations. The extremely weak spectral onset at 3.557 eV shows eight vibrational peaks, which following previous analyses, are attributed to a forbidden 1A2 state. A contrasting broad peak with a maximum at 5.381 eV has a relatively high cross-section of 30 Mb; this arises from three overlapping states, where a 1A1 state dominates over progressively weaker 1B2 and 1B1 states. After fitting the second band to a polynomial Gaussian function and plotting the regular residuals over 20 vibrational peaks, we have had limited success in analyzing this fine structure. However, the small separation between these three states clearly shows that their vibrational satellites must overlap. Singlet valence and Rydberg state vibrational profiles were determined by configuration interaction using the CAM-B3LYP density functional. Vibrational analysis using both the Franck–Condon and Herzberg–Teller procedures showed that both procedures contributed to the profiles. Theoretical Rydberg states were evaluated by a highly focused CI procedure. The superposition of the lowest photoelectron spectral band on the vacuum ultraviolet spectrum near 6.4 eV shows that the 3s and 3p Rydberg states based on the 2B2 ionic state are present; those based on the other low-lying ionic state (X2B1) are destroyed by broadening; this is a dramatic extension of the broadening previously witnessed in our studies of halogenobenzenes. [ABSTRACT FROM AUTHOR]

Lithium niobate ( LiNbO 3 , LN) on insulator (LNOI) has emerged as a promising platform for integrated photonics, due to the strong optical confinement and excellent nonlinear optical and electrical characteristics of LN crystal. Focused ion beam (FIB) as a versatile technique has become a typical way to fabricate LNOI microstructures. However, due to the bombardment of Ga + ions during fabrication, the LN lattice is damaged, which would deteriorate the performance of LNOI devices. Thus, the recognition of the damage formed by FIB fabrication is necessary for the control and optimization of the properties of LN microstructures. However, previous studies on this issue have not delved into it from a lattice perspective. Here, we conducted an investigation into the damage inflicted on LN film due to FIB fabrication and the subsequent impact of buffered oxide etching (BOE) treatment on this damage using Raman spectroscopy. Our findings indicate that the interaction between Ga + ions and LN film results in lattice amorphization, as well as a reduction in the ionic bonding and lattice stress within LN. Furthermore, absorption spectra were acquired both before and after BOE treatment, revealing the emergence of additional optical losses attributed to Ga + ions. Notably, these defects responsible for optical losses are predominantly concentrated near the surface of the milled LN film, and BOE treatment proves efficient in their removal. This study contributes to further understanding of the defect structure in LN film after FIB fabrication, as well as repairing the damage and, thus, improving the performance of LN microstructures. [ABSTRACT FROM AUTHOR]

Transient absorption (TA) spectroscopy of semiconductor nanocrystals (NCs) is often used for excited state population analysis, but recent results suggest that TA bleach signals associated with multiexcitons in NCs do not scale linearly with exciton multiplicity. In this manuscript, we probe the factors that determine the intensities and spectral positions of exciton and biexciton components in the TA spectra of CdSe quantum dots (QDs) of five diameters. We find that, in all cases, the peak intensity of the biexciton TA spectrum is less than 1.5 times that of the single exciton TA spectrum, in stark contrast to a commonly made assumption that this ratio is 2. The relative intensities of the biexciton and exciton TA signals at each wavelength are determined by at least two factors: the TA spectral intensity and the spectral offset between the two signals. We do not observe correlations between either of these factors and the particle diameter, but we find that both are strongly impacted by replacing the native organic surface-capping ligands with a hole-trapping ligand. These results suggest that surface trapping plays an important role in determining the absolute intensities of TA features for CdSe QDs and not just their decay kinetics. Our work highlights the role of spectral offsets and the importance of surface trapping in governing absolute TA intensities. It also conclusively demonstrates that the biexciton TA spectra of CdSe QDs at the band gap energy are less than twice as intense as those of the exciton. [ABSTRACT FROM AUTHOR]

Ultraviolet and vacuum ultraviolet photo-absorption spectra of azido (–N3)-based energetic plasticizer, bis(1,3-diazido-prop-2-yl)-malonate (abbreviated as BDAzPM), in the gas phase is recorded at room temperature and in the photon energy range of 5.5–9.9 eV using a synchrotron radiation source. Complementary computational results obtained using the time-dependent density functional theory document the vertical transition energies and oscillator strengths. Comparison of the simulated spectra with the experimental absorption spectrum of BDAzPM reveals that the early part of the absorption spectrum of BDAzPM is of pure valence excitation character, whereas the later intense part of the absorption spectrum is dominated by mixed Rydberg and valence electronic excitations. [ABSTRACT FROM AUTHOR]

The first-order molecular hyperpolarizability (β) dispersion was measured in seven chalcone-based molecules utilizing the tunable femtosecond hyper-Rayleigh scattering (tHRS) technique. Additionally, a theoretical model based on photophysical parameters was employed to better understand β dispersion. Due to the distinct substitution patterns of the aryl/heteroaryl rings within the chalcone structure, varying profiles of one- and two-photon absorption spectra and β dispersion were observed. The applied model highlighted two important factors contributing to achieving high β values: (i) the presence of red-shifted one-photon and two-photon absorption bands; and (ii) the number of discernible absorption bands. To contextualize these results with other molecular structures, we employed the HRS figure of merit (FOM). Remarkably, it was revealed that chemically engineered small chalcone molecules exhibit a FOM comparable to larger quadrupolar and octupolar ones. This underscores the significance of tHRS scattering measurements and their correlation with absorptive parameters in the design and characterization of nonlinear optical materials. [ABSTRACT FROM AUTHOR]

We investigate the optical properties appearing in a nanostructure that is composed of an asymmetric double semiconductor quantum dot (SQD) molecule and a metal nanoparticle (MNP). The profile of the total linear absorption spectrum is proportional to the SQD contribution, while the MNP contribution is important. The profile of the doublet of resonances detected on the total linear absorption spectrum creates a transparency window. The doublet is asymmetric for small SQD-MNP distances and has a narrow peak and a wide peak. The width of the transparency window is increased, either with the enhancement of the rate at which the electron tunneling effect takes place within the double SQD molecule or with the decrease of the distance that separates the SQD molecule from the center of the MNP. The steep slope detected on the linear dispersion spectrum for frequencies laying within the transparency window owes its presence to the tunneling induced transparency and leads to slow light production. The corresponding value of the slow down factor is maximized for low values of the electron tunneling rate as well as for low center-to-center distances between the components of the hybrid nanostructure. [ABSTRACT FROM AUTHOR]