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The adjustment of the main helical scaffold in helicenes is a fundamental strategy for modulating their optical features, thereby enhancing their potential for diverse applications. This work explores the influence of helical elongation (n = 5–9) on the structural, photophysical, and chiroptical features of symmetric oxa[n]helicenes. Crystal structure analyses revealed structural variations with helical extension, impacting torsion angles, helical pitch, and packing arrangements. Through theoretical investigations using density functional theory (DFT) calculations, the impact of helical extension on aromaticity, planarity distortion, and heightened chiral stability were discussed. Photophysical features were studied through spectrophotometric analysis, with insights gained through time‐dependent DFT (TD‐DFT) calculations. Following optical resolution via chiral high‐performance liquid chromatography (HPLC), the chiroptical properties of both enantiomers of oxa[7]helicene and oxa[9]helicene were investigated. A slight variation in the main helical scaffold of oxa[n]helicenes from [7] to [9] induced an approximately three‐fold increase in dissymmetry factors with the biggest values of|glum| of oxa[9]helicene (2.2 × 10−3) compared to|glum|of oxa[7]helicene (0.8 × 10−3), findings discussed and supported by TD‐DFT calculations. [ABSTRACT FROM AUTHOR]

A series of four novel heteroleptic Cu(I) complexes, bearing bis(1H-indazol-1-yl)methane analogues as N,N ligands and DPEPhos as the P,P ligand, were synthesised in high yields under mild conditions and characterised by spectroscopic and spectrometric techniques. In addition, the position of the carboxymethyl substituent in the complexes and its effect on the electrochemical and photophysical behaviour was evaluated. As expected, the homoleptic copper (I) complexes with the N,N ligands showed air instability. In contrast, the obtained heteroleptic complexes were air- and water-stable in solid and solution. All complexes displayed green-yellow luminescence in CH2Cl2 at room temperature due to ligand-centred (LC) phosphorescence in the case of the Cu(I) complex with an unsubstituted N,N ligand and metal-to-ligand charge transfer (MLCT) phosphorescence for the carboxymethyl-substituted complexes. Interestingly, proper substitution of the bis(1H-indazol-1-yl)methane ligand enabled the achievement of a remarkable luminescent yield (2.5%) in solution, showcasing the great potential of this novel class of copper(I) complexes for potential applications in luminescent devices and/or photocatalysis. [ABSTRACT FROM AUTHOR]

In this paper, several Ir (III) complexes with transition metal as the central atom formed by the corresponding combination of two main ligands and three auxiliary ligands have been studied theoretically. The electronic structure, frontier molecular orbital, and spin orbit coupling data are used to analyze its application value in light emitting devices. The density functional theory is used to study (tbi)2Ir(bpp), (tbi‐c)2Ir(bpp), (tbi)2Ir(dbm), (tbi‐c)2Ir(dbm), (tbi)2Ir(pic), and (tbi‐c)2Ir(pic). bpp = (2Z)‐3‐hydroxy‐13‐diphenylprop‐2‐en‐1‐one; dbm = 1,3‐di‐phenyl‐1, 3‐propanedione; pic = picolinate. [ABSTRACT FROM AUTHOR]

Graphene derivatives such as reduced graphene oxide and graphene-based composites are regarded as highly promising materials for optoelectronics and photodetection applications. Recently, considerable interest has arisen in using facile and environmentally friendly methods of graphene production. Despite significant progress in experimental studies of graphene and graphene-based composites, some fundamental questions about their structures, and the interaction between components in these systems, remain open. In the present work, several atomistic models of oxidized graphene fragments have been proposed based on XPS compositional analysis and DFT calculations, representing reduced graphene oxide produced by laser irradiation. The composition of the oxygen-containing functional groups, their equilibrium configuration and influence on the electronic and optical properties of graphene sheets were determined. The nature of the low-lying excited states, as well as the photoactive regions, has also been studied for the proposed models. The calculated absorption spectra of the graphene sheets were compared with experimental UV-Vis spectrum of rGO produced by laser ablation. [ABSTRACT FROM AUTHOR]

A series of four novel heteroleptic Cu(I) complexes, bearing bis(1H-indazol-1-yl)methane analogues as N,N ligands and DPEPhos as the P,P ligand, were synthesised in high yields under mild conditions and characterised by spectroscopic and spectrometric techniques. In addition, the position of the carboxymethyl substituent in the complexes and its effect on the electrochemical and photophysical behaviour was evaluated. As expected, the homoleptic copper (I) complexes with the N,N ligands showed air instability. In contrast, the obtained heteroleptic complexes were air- and water-stable in solid and solution. All complexes displayed green-yellow luminescence in CH2Cl2 at room temperature due to ligand-centred (LC) phosphorescence in the case of the Cu(I) complex with an unsubstituted N,N ligand and metal-to-ligand charge transfer (MLCT) phosphorescence for the carboxymethyl-substituted complexes. Interestingly, proper substitution of the bis(1H-indazol-1-yl)methane ligand enabled the achievement of a remarkable luminescent yield (2.5%) in solution, showcasing the great potential of this novel class of copper(I) complexes for potential applications in luminescent devices and/or photocatalysis.

Molecular solar‐thermal systems (MOST) have emerged in these last years as a novel concept to store solar light. They rely on two state molecular switches that can absorb a photon to convert the initial state A to a higher‐in‐energy state B. The chemical energy stored by B can be then released to reconstitute A. Although simple in its principle, an optimal MOST needs to satisfy several requirements: incoming photon energy in the solar spectrum range, high photoreaction quantum yield, high storage density, no degradation. The first challenge is therefore the search for molecular switches that accomplish all such properties. Until now, trial‐and‐error experiments have been performed, led by physicochemical intuition. The result is that most of the initially proposed switches have been abandoned in favor of the preferred norbornadiene/quadricyclane system, together with its derivatives. Nevertheless, most of the solar spectrum is still out of the MOST absorption region, hence requiring novel approaches. Here, it is shown how mechanochemistry can be applied to improve the principally desired characteristics of a MOST: photon absorption energy, storage energy, and thermal B‐to‐A energy barrier. It is especially shown how azobenzene—a paradigmatic photoswitch still attracting much attention—can be proposed, within certain limits, as a MOST when applying external forces. [ABSTRACT FROM AUTHOR]

Graphene derivatives such as reduced graphene oxide and graphene-based composites are regarded as highly promising materials for optoelectronics and photodetection applications. Recently, considerable interest has arisen in using facile and environmentally friendly methods of graphene production. Despite significant progress in experimental studies of graphene and graphene-based composites, some fundamental questions about their structures, and the interaction between components in these systems, remain open. In the present work, several atomistic models of oxidized graphene fragments have been proposed based on XPS compositional analysis and DFT calculations, representing reduced graphene oxide produced by laser irradiation. The composition of the oxygen-containing functional groups, their equilibrium configuration and influence on the electronic and optical properties of graphene sheets were determined. The nature of the low-lying excited states, as well as the photoactive regions, has also been studied for the proposed models. The calculated absorption spectra of the graphene sheets were compared with experimental UV-Vis spectrum of rGO produced by laser ablation.

In the present research, an electron donor‐acceptor (push‐pull) compound based on [7] circulene was studied using density functional theory (DFT) methods. The electron donor and acceptor units were attached to [7] circulene to improve optical properties. It was demonstrated that the band gap of [7]circulene molecule was lowered in electron donor and acceptor groups' presence, also the CN‐CIR7‐NHLi and CF3‐CIR7‐NHLi molecules have the lowest values of the band gap. It was observed that the optical properties of [7]circulene molecule was improved in the presence of electron donor and acceptor units. Between these units, the ‐CN and ‐CF3 as electron acceptors and ‐NHLi substituents as electron donor groups have higher enhancements on optical properties of circulene which is corresponding to the results obtained for energy gap values. The electric dipole moment (𝜇D) and the charge transfer, the electronic properties, polarizability (α), and first hyperpolarizability (β) values of the investigated molecules have been also computed. The results of this research may be useful in designing new materials applicable as improved photosensitizer and photodynamic therapy. All calculations and analyses are carried out by using DFT and dependent time DFT (TD‐DFT) with the B3LYP/6–311G (d,p) model in the Gaussian 09 software packages. [ABSTRACT FROM AUTHOR]

Hybrid interfaces formed by inorganic semiconductors and organic molecules are intriguing materials for opto-electronics. Interfacial charge transfer is primarily responsible for their peculiar electronic structure and optical response. Hence, it is essential to gain insight into this fundamental process also beyond the static picture. Ab initio methods based on real-time time-dependent density-functional theory coupled to the Ehrenfest molecular dynamics scheme are ideally suited for this problem. We investigate a laser-excited hybrid inorganic/organic interface formed by the electron acceptor molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ) physisorbed on a hydrogenated silicon cluster, and we discuss the fundamental mechanisms of charge transfer in the ultrashort time window following the impulsive excitation. The considered interface is p-doped and exhibits charge transfer in the ground state. When it is excited by a resonant laser pulse, the charge transfer across the interface is additionally increased, but contrary to previous observations in all-organic donor/acceptor complexes, it is not further promoted by vibronic coupling. In the considered time window of 100 fs, the molecular vibrations are coupled to the electron dynamics and enhance intramolecular charge transfer. Our results highlight the complexity of the physics involved and demonstrate the ability of the adopted formalism to achieve a comprehensive understanding of ultrafast charge transfer in hybrid materials.

The UV–visible spectra of a series of subphthalocyanines (SubPcs) characterized by three different axial substituents (An) in combination with H, F, NO2, SO2H and SO2CH3 peripheral substituents (Ri) were predicted and analyzed by means of time-dependent DFT calculations, including chloroform as a solvent. In this analysis, we paid particular attention to the Q band, which remained almost unchanged regardless of the nature of the axial substituent. For the same axial substituent, changes in the Q band were also rather small when hydrogens at the periphery were replaced by R1 = SO2H and R1 = R2 = SO2H. However, the shifting of the Q band was almost 10 times larger when R1 = NO2 and R1 = R2 = NO2 due to the participation of this substituent in the π SubPc cloud. In most cases, the characteristics of the spectra can be explained considering only the transitions involving the HOMO-1, HOMO, LUMO and LUMO + 1 orbitals, where the Q band can be decomposed into two main contributions, leading to charge separation. Only for SubPc(A3,F,F,H) would one of the two contributions from the deepest orbital involved not lead to charge transfer. For this latter case, the HOMO-2 orbital must also be taken into account. In summary, the results obtained with the analysis of the MO indicate that the studied SubPcs are appropriate for photochemical devices.

In this research, the circulene molecule was selected, and the electron donor and acceptor groups were attached to improve its optical properties. Large negative values of enthalpies, Gibbs free energies, and exothermic energies of formation for these molecules, especially for the CN-CIR-NHLi molecule, show that their formation is highly reasonable. It was illustrated that the Eg of the circulene molecule was lowered in the electron donor and acceptor groups' presence, while the CN-CIR-NHLi and CF3-CIR-NHLi molecules have the lowest values of Eg. It was observed that the optical properties of circulene molecules were improved in electron donor and acceptor groups' presence. Between these groups, the -CN and -CF3 as electron acceptors and -NHLi substituents, as electron donor groups, yield higher enhancements on the optical properties of circulene, which is in agreement with the results obtained for Eg values. [ABSTRACT FROM AUTHOR]

The perovskite CH3NH3PbI3 excited‐state lifetimes exhibit conflicting experimental results under humid environments. Using ab initio nonadiabatic (NA) molecular dynamics, we demonstrate that the interplay between lead vacancy and water can rationalize the puzzle. The lead vacancy reduces NA coupling by localizing holes, slowing electron–hole recombination. By creating a deep electron trap state, the coexistence of a neutral lead vacancy and water molecules enhances NA coupling, accelerating charge recombination by a factor of over 3. By eliminating the mid‐gap state by accepting two photoexcited electrons, the negatively charged lead vacancy interacting with water molecules increases the carrier lifetime over 2 times longer than in the pristine system. The simulations rationalize the positive and negative effects of water on the solar cell performance exposure to humidity. [ABSTRACT FROM AUTHOR]

The primary challenge of spectroscopic techniques in selective detection and characterization of tautomeric structures of DNA and RNA bases, and moreover, the accurate interpretation and explanation of the experimental results are the main motives of theoretical studies. Surface‐enhanced Raman spectroscopy (SERS) can be a powerful approach to distinguish cytosine in the presence of its tautomers. For this respect, herein, the theoretical simulation of the SERS spectra of cytosine and its three most stable tautomers adsorbed on silver clusters is carried out. The calculations of SERS spectra is based on the excited‐state energy gradient approximation as a well‐established approach that gives us the knowledge about the properties of excited states and their effect on the pattern of spectra. The good consistency of this theoretical simulation in solution and also the gas phase with the experimental results is achieved and represents the capacity of the current theoretical investigations to interpret and supplement the experimental findings. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • New star like ferrocenyl compounds containing two different central cores have been synthesized. • The oxidation of ferrocenyl is facilitated by conjugation of vinyl linker through central core. • Bathochromic shift in absorption spectra was observed based on the nature of linker. Abstract New ferrocenyl-subtituted compounds containing two different central cores (isocyanurate and 1,3,5-phenylene) and extended by two kinds of branches bearing both vinyl ferrocenyl (1 and 3) and cross-conjugated ferrocenyl-chalcone (2, 4 and 5) as endgroups have been synthetized and characterized both spectroscopically and electrochemically. These molecules have been synthesized in order to investigate the electronic properties imparted by both types of branches when they are connected to the central core. For all compounds, electrochemical studies have showed a simultaneous oxidation of all ferrocene units present in each compound. For all of them, except for compound 2 , a chemically reversible oxidation wave on the voltammograms has been observed. In contrast, for compound 2, a chemically irreversible oxidation wave is obtained. Moreover, the vinyl ferrocenyl derivatives have presented a lower redox peak potential with respect to ferrocene standard compound, and the ferrocenyl-chalcone bearing derivatives, in accordance with a change in the electron releasing capability of these endgroups, have been oxidized at a higher potential. Bathochromic shifts of the active transitions in Uv-Vis region have been observed, which are associated to the presence of carbonyl groups in those molecular structures containing it. These results are in agreement with theoretically calculated transition energies, which have been obtained for compounds 1 and 2 using Time Dependent Density Functional Theory (TD-DFT). [ABSTRACT FROM AUTHOR]

Graphical abstract Herein, an indirect SOC route is clarified: the 1MLCT state interacts by SOC with the 3MLCT state; meanwhile the 3MLCT state interacts by CI with the 3LLCT state. Consequently, the interaction between 1MLCT and 3LLCT may be seen to be the cooperation of SOC and CI. The SOC between 1MLCT and 3MLCT is effective and strong, because it involves one-center integral and the corresponding matrix element is large. Consequently, the interaction between 1MLCT and 3LLCT lies ultimately in the effectiveness of CI between 3MLCT and 3LLCT. Abstract Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were applied to investigate the electronic structures and photophysical properties of a series of phosphorescent iridium (III) complexes, [(C∧N) 2 Ir(N∧N)]+(PF 6)−, in which C∧N = 4-aryl-1-benzyl-1H-1, 2, 3-triazoles. Herein, aryl = phenyl, biphenyl, three-phenyl aromatic for complexes 1a, 2a, 3a (N∧N = 2, 2′-bipyridine) and aryl = 4′, 6′-difluorophenyl, 6′-fluoro-biphenyl, 6′-fluoro-three-phenyl aromatic for complexes 1b, 2b, 3b (N∧N = 4, 4′-di- tert -butyl-2, 2′-bipyridine), respectively. The geometric/electronic configurations, absorption/emission properties and phosphorescent performances have been outlined for each of the complexes. Based on the two simplifications presented in this paper and the available experimental data, the phosphorescent radiative rates for complexes 1a-3b were approximately obtained to be: 1.20 × 106 s−1, 1.68 × 105 s−1, 2.19 × 107 s−1, 3.85 × 106 s−1, 1.85 × 107 s−1 and 1.50 × 107 s−1, respectively. In view of the electroluminescent applications in OLED, our present research work is of great importance for the design and synthesis of organo-transition metal complexes with improved phosphorescent performances. [ABSTRACT FROM AUTHOR]

FeIFeI Fe2(S2C3H6)(CO)6(µ-CO) (1a–CO) and its FeIFeII cationic species (2a+–CO) are the simplest model of the CO-inhibited [FeFe] hydrogenase active site, which is known to undergo CO photolysis within a temperature-dependent process whose products and mechanism are still a matter of debate. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) computations, the ground state and low-lying excited-state potential energy surfaces (PESs) of 1a–CO and 2a+–CO have been explored aimed at elucidating the dynamics of the CO photolysis yielding Fe2(S2C3H6)(CO)6 (1a) and [Fe2(S2C3H6)(CO)6]+ (2a+), two simple models of the catalytic site of the enzyme. Two main results came out from these investigations. First, a–CO and 2a+–CO are both bound with respect to any CO dissociation with the lowest free energy barriers around 10 kcal mol−1, suggesting that at least 2a+–CO may be synthesized. Second, focusing on the cationic form, we found at least two clear excited-state channels along the PESs of 2a+–CO that are unbound with respect to equatorial CO dissociation.

[Display omitted] • Dimethylacridan and phenothiazine-5,5-dioxide-based compounds were synthesized. • Media polarity influenced emission properties ranging from LE to HLCT and CT. • Para -isomer demonstrated more efficient triplet harvesting in OLEDs than the meta -one. Aiming to combine the advantages of both prompt fluorescence and thermally activated delayed fluorescence in single emitter, molecular design of emitters with hybridized locally excited and charge transfer states were investigated by computational approaches and optical spectroscopy. Taking into account the results of the theoretical screening, the most promising derivatives of 9,9-dimethyl-9,10-dihydroacridine and 10-phenyl-10 H -phenothiazine-5,5-dioxide based with the different linking topology (meta - and para -isomers) were selected for the synthesis and experimental investigations. Both the compounds exhibit ultraviolet LE emission peaking at ca. 360 nm, green ICT peaking at ca. 510 nm, and deep-blue HLCT emission peaking at ca. 430 nm when they are molecularly dispersed in the solid media of the different polarity. The developed emitters allow to obtain deep-blue electroluminescence for the host-containing OLEDs and green electroluminescence of host-free devices with the efficiency of exciton production of 42 and 73%, respectively. Efficient exciton production is due to the spin-flip switching via thermally activated processes which is much more efficient than prompt fluorescence. Showing the impact of the linking topology, the para -isomer demonstrated more efficient triplet harvesting in OLEDs than meta -isomer. A detailed discussion on the structure–property relationships and on some discrepancies between the results of the results of theoretical calculations and spectral analysis allows to obtain important insights on the photophysical properties of these compounds. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hydration structure of caffeine diluted in ambient liquid water has been studied using classical MD simulations. • The results obtained have revealed that the first hydration shell of caffeine contains on average 56 water molecules. • Hydrated caffeine forms in total 3 hydrogen bonds with its neighbor water molecules. • The water molecules within the first hydration shell of caffeine significantly change their translational and reorientational dynamics relative to the bulk. • Quantum chemical calculations have predicted the UV–Vis and fluorescence spectra of hydrated caffeine, in agreement with recent experimental data. The hydration structure and related dynamics of caffeine diluted in ambient liquid water have been extensively studied by performing classical molecular dynamics simulations, using our previously developed potential model of caffeine and the TIP4P/2005 water model. The results obtained have revealed that the first hydration shell of caffeine contains on average 56 water molecules. Hydrated caffeine forms in total 3 hydrogen bonds with its neighbor water molecules, with the O caffeine ... H water hydrogen bonds exhibiting similar lifetimes with the ones corresponding to O water ... H water hydrogen bonds in liquid water. The self-diffusion coefficient of caffeine has been found to be four times lower than the corresponding value for water, being also in agreement with recent experimental measurements. The presence of water molecules inside the solvation shell of caffeine changes significantly their low-frequency intermolecular vibrations, as reflected on the calculated atomic velocity time correlation functions and corresponding spectral densities. Using the estimated average intermolecular structure of the first hydration shell of caffeine, the molecular cluster caffeine@W 56 was optimized via quantum chemical calculations and subsequently the time-dependent density functional theory was used in order to predict the ultraviolet–visible and fluorescence spectra of hydrated caffeine. The results obtained are in agreement with recent experimental studies, which have proposed that such spectroscopic measurements can be used for the direct determination of alkaloids in aqueous extracts of natural products. In this framework, multi-scale molecular modelling providing accurate predictions of experimental data could also be a very useful tool, linking theoretical physical chemistry with analytical chemistry applications. [ABSTRACT FROM AUTHOR]

A series of four novel heteroleptic Cu(I) complexes, bearing bis(1 H -indazol-1-yl)methane analogues as N , N ligands and DPEPhos as the P,P ligand, were synthesised in high yields under mild conditions and characterised by spectroscopic and spectrometric techniques. In addition, the position of the carboxymethyl substituent in the complexes and its effect on the electrochemical and photophysical behaviour was evaluated. As expected, the homoleptic copper (I) complexes with the N , N ligands showed air instability. In contrast, the obtained heteroleptic complexes were air- and water-stable in solid and solution. All complexes displayed green-yellow luminescence in CH 2 Cl 2 at room temperature due to ligand-centred (LC) phosphorescence in the case of the Cu(I) complex with an unsubstituted N,N ligand and metal-to-ligand charge transfer (MLCT) phosphorescence for the carboxymethyl-substituted complexes. Interestingly, proper substitution of the bis(1 H -indazol-1-yl)methane ligand enabled the achievement of a remarkable luminescent yield (2.5%) in solution, showcasing the great potential of this novel class of copper(I) complexes for potential applications in luminescent devices and/or photocatalysis.

Abstract The present study aimed to evaluate a class of A-D-π-D-A organic dyes by replacing central π-spacer by fused electron rich(D) and electron deficient(A) moieties (D-A) with different configurations in order to shed light on the role of the structure of fused π-bridge on the cell performance. In addition, the effect of the structure of side chain on the N-atom of donor was investigated. The electronic and optical properties of the dyes and dye-TiO 2 complexes, which are relevant to the short circuit photocurrent density and open circuit photovoltage, were comprehensively analyzed. The results indicated that the correct choice of side chain results in improving V OC while the molecular engineering of the side chain on the donor plays an insignificant effect on the electronic and optical properties of dyes. Further, the effect of the strength of auxiliary acceptor on the performance of dyes was evaluated. Based on the results, the π-linkers including the moderate auxiliary acceptor with the DTP unit could improve intramolecular charge transfer parameters and the light harvesting efficiency, reduce the continuity multiple charge transfer pathways, and enhance electron injection to TiO 2 semiconductor. The results can provide a helpful guidance to design high-performance di-anchoring dyes. Graphical abstract Image 1 Highlights • The role of the structure of the fused π-spacer on the cell performance was explored. • The electronic and optical properties of dyes and dye-TiO 2 complexes were comprehensively analyzed. • The A-D-π-D-A dye with the π-linker including moderate auxiliary acceptor fused with a DTP subunit performs nicely. [ABSTRACT FROM AUTHOR]

The performance of the strongly constrained and appropriately normed (SCAN) meta-generalised gradient approximation exchange-correlation functional is investigated for the calculation of time-dependent density-functional theory molecular excitation energies of local, charge-transfer and Rydberg character, together with the excited potential energy curve in H2. The SCAN results frequently resemble those obtained using a global hybrid functional, with either a standard or increased fraction of exact orbital exchange. For local excitations, SCAN can exhibit significant triplet instability problems, resulting in imaginary triplet excitation energies for a number of cases. The Tamm-Dancoff approximation offers a simple approach to improve the situation, but the excitation energies are still significantly underestimated. Understanding the origin of these (near)-triplet instabilities may provide useful insight into future functional development. [ABSTRACT FROM AUTHOR]

Hypothesis In photorheological fluids, subtle molecular changes caused by light lead to abrupt macroscopic alterations. Upon UV irradiation of an aqueous cetyltrimethylammonium bromide (CTAB) and trans -ortho-methoxycinnamic acid ( trans -OMCA) solution, for instance, the viscosity drops over orders of magnitude. Multiscale modeling allows to elucidate the mechanisms behind these photorheological effects. Experiments We use time-dependent DFT calculations to study the photoisomerization, and a combination of atomistic molecular dynamics (MD) and DFT to probe the influence of both OMCA isomers on the micellar solutions. Findings The time-dependent DFT calculations show that the isomerization pathway occurs in the first triplet excited state with a minimum energy conformation closest to the after photoisomerization predominant cis configuration. In the MD simulations, with sub-microsecond timescales much shorter than the experimental morphological transition, already a clear difference is observed in the packing of the two OMCA isomers: contrary to trans -OMCA, cis -OMCA exposes notable part of its hydrophobic aromatic rings at the micelle surface. This can explain why trans -OMCA adopts rod-like micellar packing (high viscosity) while cis -OMCA spherical micellar packing (low viscosity). Moreover, lowering of the OMCA co-solute concentration allowed us to perform full simulation of the breakup process of the rod-like micelles which are stable prior to isomerization. [ABSTRACT FROM AUTHOR]

In this work, we summarize the recent progress made in constructing time-dependent density-functional theory (TDDFT) exchange-correlation (XC) kernels capable to describe excitonic effects in semiconductors and apply these kernels in two important cases: a "classic" bulk semiconductor, GaAs, with weakly-bound excitons and a novel two-dimensional material, MoS2, with very strongly-bound excitonic states. Namely, after a brief review of the standard many-body semiconductor Bloch and Bethe-Salpether equation (SBE and BSE) and a combined TDDFT+BSE approaches, we proceed with details of the proposed pure TDDFT XC kernels for excitons. We analyze the reasons for successes and failures of these kernels in describing the excitons in bulk GaAs and monolayer MoS2, and conclude with a discussion of possible alternative kernels capable of accurately describing the bound electron-hole states in both bulk and two-dimensional materials. [ABSTRACT FROM AUTHOR]

The foundation of many approximations in time-dependent density functional theory (TDDFT) lies in the theory of the homogeneous electron gas. However, unlike the ground-state DFT, in which the exchange-correlation potential of the homogeneous electron gas is known exactly via the quantum Monte Carlo calculation, the time-dependent or frequency-dependent dynamical potential of the homogeneous electron gas has not been known exactly, due to the absence of a similar variational principle for excited states. In this work, we present a simple geometric derivation of the time-dependent dynamical exchange-correlation potential for the homogeneous system. With this derivation, the dynamical potential can be expressed in terms of the stress tensor, offering an alternative to calculate the bulk and shear moduli, two key input quantities in TDDFT. [ABSTRACT FROM AUTHOR]

We present a description of the optical properties of a water-soluble BODIPY derivative in the gas phase and in water. Comparison with a hydrophobic BODIPY derivative with very similar structure but deprived of the hydrophilic groups, clarifies the effects of functionalization. The changes in solution are studied at different levels of modeling. In particular, we make use of Car–Parrinello molecular dynamics to take thermal motion into account, by generating a set of molecular configurations at about room temperature and embedding them in the polarizable continuum model (PCM) for the solvent. The theoretical scheme is that of time-dependent density functional theory which we apply using different approximations for the exchange-correlation functionals. Changes in the low-lying excitation spectrum (≈2.5–4.5 eV) of the solvated molecule in water relative to gas phase are shown to be due not only to the electrostatic interaction with the solvent but also to the thermal motion that induces a downward energy shift and broadening of the absorption lines. Addition of explicit water molecules to the PCM only affects spectral features at higher energies. [ABSTRACT FROM AUTHOR]

The electronic structures and photophysical properties of a series of cyclometalated iridium (III) complexes Ir(C ∧ N) 2 (H 2 NNHCOO), including 1 [C ∧ N=2-phenyl-pyridine], 2 [C ∧ N=5-fluoro-2-phenylpyridine], 3 [C ∧ N=2-phenyl-5-trifluoromethylpyridine], 4 [C ∧ N=6-phenyl-[2, 3] bipyridinyl], 5 [C ∧ N=7-phenyl-cyclopenta [4] dipyridine] and 6 [C ∧ N=8-phenyl-[1, 9] phenanthroline], have been theoretically investigated based on density functional theory (DFT) and time-dependent DFT. The characteristics in phosphorescent performances have been outlined for each of the complexes in the applications in OLED. On the basis of the two simplifications presented in this paper and the available experimental data, the magnitudes of phosphorescent radiative rates for complexes 1–6 were approximately calculated to be: 5.56×10 5 s −1 , 2.68×10 5 s −1 , 1.17×10 6 s −1 , 9.78×10 4 s −1 , 5.30×10 6 s −1 and 6.71×10 6 s −1 , respectively. Meanwhile, the sequence of phosphorescent quantum efficiencies was obtained to be: Ф PL (4)< Ф PL (2)< Ф PL (1)< Ф PL (3)< Ф PL (5)< Ф PL (6), in which Ф PL (4) is by far the lowest, Ф PL (5) is much larger and Ф PL (6) is by far the largest. In contrast to complex 1, the emission wavelengths are slightly red-shifted for 2 and 3 and significantly red-shifted for 4 and 5, while the emission wavelength of 6 is slightly blue-shifted. In comparison, complexes 6 and 5 may be singled out to be the most efficient phosphorescence emitters for the applications in OLED. [ABSTRACT FROM AUTHOR]

Based on the quantum chemistry methodologies, the electronic structures and photophysical properties have been investigated for a series of cyclometalated iridium(III) complexes Ir(C^N) 2 (acac), including 1 [C^N = 2-biphenyl-4-yl-quinoline], 2 [C^N = 2-(fluoren-2-yl)-quinoline], 3 [C^N = 2-dibenzofuran-3-yl-quinoline], 4 [C^N = 2-dibenzothiophen-3-yl-quinoline] and 5 [C^N = 2-phenanthren-2-yl-quinoline]. The electronic configurations, absorption properties, emission wavelengths and the potential phosphorescent performances have been outlined for each of the complexes. On the basis of the two simplifications presented in this paper and the available experimental data, the magnitudes of phosphorescent radiative rates for each of the complexes were approximately calculated to be: 1.20 × 10 5 s −1 , 8.75 × 10 4 s −1 , 3.58 × 10 5 s −1 , 5.69 × 10 4 s −1 and 4.73 × 10 4 s −1 , respectively. Meanwhile, the sequence of phosphorescent quantum efficiencies was obtained to be: Ф PL ( 3 ) > Ф PL ( 1 ) > Ф PL ( 2 ) > Ф PL ( 5 ) > Ф PL ( 4 ). Our research work is of great importance, consulting the quantum chemistry conclusions and applying adequate chemical engineering, it may be possible to obtain cyclometalated iridium(III) complexes with distinctly improved phosphorescent performances in the application in OLED. [ABSTRACT FROM AUTHOR]

In this work, we summarize the recent progress made in constructing time-dependent density-functional theory (TDDFT) exchange-correlation (XC) kernels capable to describe excitonic effects in semiconductors and apply these kernels in two important cases: a “classic” bulk semiconductor, GaAs, with weakly-bound excitons and a novel two-dimensional material, MoS2, with very strongly-bound excitonic states. Namely, after a brief review of the standard many-body semiconductor Bloch and Bethe-Salpether equation (SBE and BSE) and a combined TDDFT+BSE approaches, we proceed with details of the proposed pure TDDFT XC kernels for excitons. We analyze the reasons for successes and failures of these kernels in describing the excitons in bulk GaAs and monolayer MoS2, and conclude with a discussion of possible alternative kernels capable of accurately describing the bound electron-hole states in both bulk and two-dimensional materials.

Organic-based photovoltaic devices emerged as a complementary technology to silicon solar cells with specific advantages in terms of cost, ease of deployment, semi-transparency, and performance under low and diffuse light conditions. In this work, thin-film boron-doped diamond (B:NCD) electrodes are employed for their useful optical, electronic, and chemical properties, as well as stability and environmental safety. A set of oligothiophene perylene diimide (nT-PDI) donor-acceptor chromophores is designed and synthesized in order to investigate the influence of the oligothiophene spacer length when the nT-PDI molecule is attached to a B:NCD electrode. The chromophores are anchored to the diamond surface via diazonium grafting followed by Sonogashira cross-coupling. X-ray photoelectron spectroscopy shows that the surface coverage decreases with increasing oligothiophene length. Density functional theory (DFT/TDDFT) calculations reveal the upright nT-PDI orientation and the most efficient photogenerated charge separation and injection to diamond for elongated oligothiophene chains (8T-PDI). Yet, the maximum photovoltage is obtained for an intermediate oligothiophene length (3T-PDI), providing an optimum between decreasing transport efficiency and increasing efficiency of charge separation and reduced recombination with increasing oligothiophene length. Holes transferred from nT-PDI to diamond persist there even after the illumination is switched off. Such features may be beneficial for application in solar cells. [Display omitted] • Variable donor-acceptor chromophore/diamond system designed in-silico and fabricated. • Oligothiophene donor length adjusts valence band and charge transport with diamond. • Intermediate oligothiophene length (3 units) yields the maximum photovoltage. • Up to 0.87 electron per molecule transferred to diamond across 44 Å under excitation. [ABSTRACT FROM AUTHOR]

The limitations of author's modification of the well-known method for determination of water content in organic solvents with chloranilic acid (CAA) [Anal. Chim. Acta 16 (1962) 494] are illustrated. An insight into the CAA solvatochromism at the molecular level is proposed on the basis of quantum-chemical calculations. The bathochromic shift is explained by CAA anion formation in an interaction with the solvent. Deprotonation of CAA depends substantially on the solvent, both on the first solvation shell microstructure and on the bulk solvent phase. The deprotonation equilibrium, responsible for the long-wavelength absorption, limits applicability of the analytical method. [ABSTRACT FROM AUTHOR]

Cholesterol ( Chol ) and ergosterol ( Erg ) are abundant and important sterols in the plasma membrane of mammalian and yeast cells, respectively. The effects of Chol and Erg on membrane properties, as well as their intracellular transport, can be studied with use of fluorescence probes mimicking both sterols as closely as possible. In the search for new and efficient Chol and Erg probes, we use a combination of theoretical methods to explore a series of analogs. The optical properties of the analogs (i.e. excitation energies, emission energies and oscillator strengths) are examined using time-dependent density functional theory (TDDFT) and their ability to mimic the effects of Chol and Erg on membranes is investigated with molecular dynamics (MD) simulations of each analog in a 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer. From the set of analogs we find two probes ( 3a and 3b ) to display favorable electronic transition properties as well as strong condensing abilities. These findings can lead to the use of new efficient probes and aid in the understanding of the structural features of Chol and Erg that impart to them their unique effects on lipid membranes. [ABSTRACT FROM AUTHOR]

We investigate the local polarisability or polarisability density using both a conceptual density functional theory approach based on the linear response function and time-dependent density functional theory. Using a zero frequency in the latter, we can immediately compare both approaches. Using an analytical expression for the linear response kernel, we are able to systematically analyse α(r) throughout the periodic table. An extension to molecules is also made with a study of the CO molecule retrieving the connection between local softness and local polarisability. [ABSTRACT FROM PUBLISHER]

The UV/Vis titration measurements, vibrational and NMR spectroscopy of isomeric dehydrodibenzopyrido[15]annulenes (DBPA) 1 and 2 clearly show that under proper conditions these macrocycles can achieve fast, quantitative and unselective binding of metal ions. The macrocycle 1 is an example of a hindered amine 2,6-bis(R)pyridine and its isomer 2 of a non-hindered amine 3,5-bis(R)pyridine. The protonation stoichiometry for both 1 and 2 was assumed to be DBPA:H + = 1:1 and the formation constants log K = 4.77 ± 0.02 for 1 , and log K = 6.78 ± 0.08 for 2 were obtained that well agree with those obtained under similar conditions for a macrocycle containing bipyridine units. The protonation of 2 gave the estimated stoichiometry of 2 :H + = 1:1 while the stoichiometric protonation of macrocycle 1 could not be achieved and the lower stability of the ion pair containing 1 H + is most likely due to the inaccessibility of the nitrogen atom of 1 to the counterions and solvent molecules. The structures and electronic absorption spectra of 1 and 2 , as well as the structures and spectra of 1 H + and 2 H + , i.e. the species formed by protonation of the pyridine nitrogen, were calculated with the time-dependent DFT method with a B3LYP functional and a 6-31+G(d) basis set. The solvent effects were incorporated by means of the polarizable continuum model (PCM). The agreement of the calculated absorption data for the parent and protonated species with the observed spectra is rather satisfactory. Vibrational IR and Raman spectra of 1 , 2 , 1 H + and 2 H + in vacuo were calculated at the B3LYP/cc-pVTZ level of theory. Macrocycles 1 and 2 , and their products protonated by trifluoromethanesulfonic acid ( 1 HOTf and 2 HOTf) were also characterized by temperature-dependent FTIR technique known as two dimensional IR correlation analysis. Quite large difference in degradation temperature between macrocycle 1 and 2 and their protonated complexes was measured, indicating that inclusion of proton leads to significant thermal stabilization of dehydroannulene ring. [ABSTRACT FROM AUTHOR]

A series of organic donor-π-acceptor dyes with difference in π spacer have been designed and investigated theoretically as sensitizers for application in dye-sensitized solar cells. Density functional theory and time-dependent density functional theory calculations reveal how the additional electron-withdrawing diketopyrrolopyrrole unit and π spacer order influence the physical properties of the dyes, including spectral response, light harvesting efficiency, and electron injection rate. The results show that auxiliary acceptor leads to the greatly red-shifted of the charge-transfer absorption band. Meanwhile, the number and sort order of thiophene groups can significantly tune the orbital energy levels and change the electronic transition processes. The thiophene groups locating between triphenylamine and diketopyrrolopyrrole units would conduce to the light absorption and electron injection efficiency. The results also suggest that the donor-acceptor-π-acceptor type dyes have indirect electron injection mode compared with the direct mode in the dyes without containing diketopyrrolopyrrole. [ABSTRACT FROM AUTHOR]

The influence of structural order on the electronic and optical properties of C60/P3HT bulk heterojunctions (BHJs) was studied using first principles DFT and TDDFT methods. The electronic levels alignment between the two phases in the BHJs is mainly controlled by the interfacial dipole moment that shifts the P3HT electronic levels towards higher binding energies with respect to C60 levels. An increasing order translates into an increasing P3HT domains size, for which we considered different stacks of P3HT oligomers. A significant decrease of both the electronic (HOMOP3HT-LUMOC60) and the optical (HOMOP3HT-LUMOP3HT) band gap is observed with an increasing P3HT domain size. TDDFT approach was used to identify the orbitals involved in the electronic transitions, and to reveal that the reduction of the BHJ optical band gap cannot simply be predicted from the variation of the rrP3HT band gap. The lowest electronic transition in rrP3HT becomes optically forbidden due to the formation of H-aggregates. [ABSTRACT FROM AUTHOR]

The solution structure of the two presently known polyoxoaurates, [Au4As4O20]8- (Au4As4) and [Au4Se4O16]4- (Au4Se4), was elucidated by a combination of time-dependent density-functional-theory (TD-DFT) calculations, experimental UV/Vis spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The TD-DFT-predicted electronic spectra for molecular models including different numbers of counterions, along with the main Au4As4 and Au4Se4 structural motifs, were analyzed and compared with the experimental UV/Vis spectra of the two polyanions. The performed analysis revealed important structural differences between the arsenate and the selenite derivatives in aqueous solution. For the selenite oxoaurate, the bare Au4Se4 polyanion itself shows very good agreement between predicted and experimental excitation energies. In contrast, the solution state of the arsenate oxoaurate appears to be best described by a dimeric assembly of the type [Na5Au8As8O40]11- (Na5Au8As8) with a stoichiometry and structure very similar to those reported for the solid state. Indirect experimental evidence that Na5Au8As8 is the dominant species in aqueous solution is provided by ESI-MS measurements. Our work demonstrates that the combination of experimental UV/Vis spectroscopy and TD-DFT calculations complemented with electrospray mass spectrometry may serve as an alternative strategy for rationalizing the solution chemistry of polyoxometalates, which cannot be studied by conventionally used spectroscopic techniques, such as NMR or EPR spectroscopy. [ABSTRACT FROM AUTHOR]

We have studied electron transfers (ET) between electron donors and acceptors, taking as illustrative example the case of ET in methionine enkephalin. Recent pulse and gamma radiolysis experiments suggested that an ultrafast ET takes place from the C-terminal tyrosine residue to the N-terminal, oxidized, methionine residue. According to standard theoretical frameworks like the Marcus theory, ET can be decomposed into two successive steps: i) the achievement through thermal fluctuations, of a set of nuclear coordinates associated with degeneracy of the two electronic states, ii) the electron tunneling from the donor molecular orbital to the acceptor molecular orbital. Here, we focus on the analysis of the time-dependent electronic dynamics during the tunneling event. This is done by extending the approaches based on the topological analyses of stationary electronic density and of the electron localization function (ELF) to the time-dependent domain. Furthermore, we analyzed isosurfaces of the divergence of the current density, showing the paths that are followed by the tunneling electron from the donor to the acceptor. We show how these functions can be calculated with constrained density functional theory. Beyond this work, the topological tools used here can open up new opportunities for the electronic description in the time-dependent domain. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a radix-4 decimation-in-frequency algorithm for the efficient computation of the short-time, discrete Fourier transform, which makes use of radix-4 butterflies with time-varying coefficients arising from a fixed time origin. The proposed scheme is successfully compared with existing competing algorithms in terms of computational cost. [Copyright &y& Elsevier]

Time-dependent quantum transport parameters for graphene nanoribbons (GNR) are calculated by the hierarchical equation of motion (HEOM) method based on the nonequilibrium Green's function (NEGF) theory [Xie et al., J. Chem. Phys. 137, 044113 (2012)]. In this paper, a new initial-state calculation technique is introduced and accelerated by the contour integration for large systems. Some Lorentzian fitting schemes for the self-energy matrices are developed to effectively reduce the number of Lorentzians and maintain good fitting results. With these two developments in HEOM, we have calculated the transient quantum transport parameters in GNR. We find a new type of surface state with delta-function-like density of states in many semi-infinite armchair-type GNR. For zigzag-type GNR, a large overshooting current and slowly decaying transient charge are observed, which is due to the sharp lead spectra and the 'even-odd' effect. [ABSTRACT FROM AUTHOR]