Simulating the coupled electronic and nuclear response of a molecule to light excitation requires the application of nonadiabatic molecular dynamics. However, when faced with a specific photophysical or photochemical problem, selecting the most suitable theoretical approach from the wide array of available techniques is not a trivial task. The challenge is further complicated by the lack of systematic method comparisons and rigorous testing on realistic molecular systems. This absence of comprehensive molecular benchmarks remains a major obstacle to advances within the field of nonadiabatic molecular dynamics. A CECAM workshop, Standardizing Nonadiabatic Dynamics: Towards Common Benchmarks, was held in May 2024 to address this issue. This Perspective highlights the key challenges identified during the workshop in defining molecular benchmarks for nonadiabatic dynamics. Specifically, this work outlines some preliminary observations on essential components needed for simulations and proposes a roadmap aiming to establish, as an ultimate goal, a community-driven, standardized molecular benchmark set.

We employ the exact-factorization formalism to study the coupled dynamics of photons, electrons, and nuclei at the quantum mechanical level, proposing illustrative examples of model situations of nonadiabatic dynamics and spontaneous emission of electron-nuclear systems in the regime of strong light-matter coupling. We make a particular choice of factorization for such a multi-component system, where the full wavefunction is factored as a conditional electronic amplitude and a marginal photon-nuclear amplitude. Then, we apply the coupled-trajectory mixed quantum-classical (CTMQC) algorithm to perform trajectory-based simulations, by treating photonic and nuclear degrees of freedom on equal footing in terms of classical-like trajectories. The analysis of the time-dependent potentials of the theory along with the assessment of the performance of CTMQC allow us to point out some limitations of the current ap- proximations used in CTMQC. On the other hand, comparing CTMQC with other trajectory-based algorithms, namely multi-trajectory Ehrenfest and Tully surface hopping, demonstrates the better quality of CTMQC predictions.

We report the formulation and implementation of an extended Frenkel exciton model (EFEM) designed for simulating the dynamics of multichromophoric systems, taking into account the possible presence of interchromophore charge transfer states, as well as other states in which two chromophores are simultaneously excited. Our approach involves constructing a Hamiltonian based on calculations performed on monomers and selected dimers within the multichromophoric aggregate. Nonadiabatic molecular dynamics is addressed using a surface hopping approach, while the electronic wave functions and energies required for constructing the EFEM are computed utilizing the semiempirical floating occupation molecular orbitals-configuration interaction (FOMO-CI) electronic structure method. To validate our approach, we simulate the singlet fission process in a trimer of 2,5-bis(fluorene-9-ylidene)-2,5-dihydrothiophene (ThBF) molecules, embedded in their crystal environment, comparing the results of the EFEM to the standard "supermolecule" approach.

We address the issues of decoherence, frustrated hops and internal consistency in surface hopping. We demonstrate that moving away from an independent-trajectory picture is the strategy which allows us to propose a robust surface hopping scheme overcoming all these issues at once. Based on the exact factorization and on the idea of coupled trajectories, we consider the swarm of trajectories, that mimics the nuclear dynamics in nonadiabatic processes, as a unique entity. In this way, imposing energy conservation of the swarm and allowing the trajectories to share energy when hops occur clearly indicates the route towards a new surface hopping scheme. Encouraging results are reported, in terms of electronic and vibrational time-dependent properties on the photodynamics of fulvene and 4-(dimethyloamino)benzonitrile, modeled with a full-dimensional linear vibronic coupling Hamiltonian.

This Perspective offers an overview on the applications of the exact factorization of the electron-nuclear wavefunction to the domain of theoretical photochemistry, where the aim is to gain insights into the ultrafast dynamics of molecular systems via simulations of their excited-state dynamics beyond the Born-Oppenheimer approximation. The exact fac- torization offers an alternative viewpoint to the Born-Huang representation for the interpretation of dynamical processes involving the electronic ground and excited states as well as their nonadiabatic coupling through the nuclear motion. Therefore, the formalism has been used to derive algorithms for quantum molecular-dynamics simulations where the nuclear motion is treated using trajectories and the electrons are treated quantum mechanically. These algorithms have the characteristic features of being based on coupled and on auxiliary trajectories, and have shown excellent perfor- mance in describing a variety of excited-state processes, as this Perspective illustrates. We conclude with a discussion on the authors’ point of view on the future of the exact factorization.

Recent developments in quantum computing are highly promising, particularly in the realm of quantum chemistry. Due to the noisy nature of currently available quantum hardware, hybrid quantum-classical algorithms have emerged as a reliable option for near-term simulations. Mixed quantum-classical dynamics methods effectively capture nonadiabatic effects by integrating classical nuclear dynamics with quantum chemical computations of the electronic properties. However, these methods face challenges due to the high computational cost of the quantum chemistry part. To mitigate the computational demand, we propose a method where the required electronic properties are computed through a hybrid quantum-classical approach that combines classical and quantum hardware. This framework employs the variational quantum eigensolver and variational quantum deflation algorithms to obtain ground and excited state energies, gradients, nonadiabatic coupling vectors, and transition dipole moments. These quantities are used to propagate the nonadiabatic molecular dynamics using the Tully's fewest switches surface hopping method, although the implementation is also compatible with other molecular dynamics approaches. The approach, implemented by integrating the molecular dynamics program package SHARC with the TEQUILA quantum computing framework, is validated by studying the cis-trans photoisomerization of methanimine and the electronic relaxation of ethylene. The results show qualitatively accurate molecular dynamics that align with experimental findings and other computational studies. This work is expected to mark a significant step towards achieving a "quantum advantage" for realistic chemical simulations.

The photoisomerization dynamics of azoescitalopram, a synthetic photoswitchable inhibitor of the human serotonin transporter, is investigated in both gas-phase and water. We use the trajectory surface hopping method, as implemented in SHARC, interfaced with the semiempirical Floating Occupation Molecular Orbitals-Configuration Interaction (FOMO-CI) electronic structure method to calculate on-the fly energies, forces and couplings. The inclusion of explicit water molecules is enabled using a quantum mechanics/molecular mechanics (QM/MM) framework. We find that the photoisomerization quantum yield of trans-azoescitalopram is wavelength and environment dependent, with n→π* excitation yielding higher quantum yields than π→π* excitation. Additionally, we observe the formation of two distinct cis-isomers during photoisomerization from the most thermodynamically stable trans-isomer, with formation rates influenced by both the excitation window and surrounding environment. Longer excited-state lifetimes are found than those reported for azobenzene, suggesting that the escitalopram moiety contributes to these extended lifetimes and slower torsional motions.

In this work, we present the first implementation of coupled-trajectory Tully surface hopping (CT-TSH) suitable for applications to molecular systems. We combine CT-TSH with the semiempirical floating occupation molecular orbital-configuration interaction electronic structure method to investigate the photoisomerization dynamics of trans-azobenzene. Our study shows that CT-TSH can capture correctly decoherence effects in this system, yielding consistent electronic and nuclear dynamics in agreement with (standard) decoherence-corrected TSH. Specifically, CT-TSH is derived from the exact factorization and the electronic coefficients' evolution is directly influenced by the coupling of trajectories, resulting in the improvement of internal consistency if compared to standard TSH.

The observable nature of topological phases related to conical intersections in molecules is studied. Topological phases should be ubiquitous in molecular processes, but their elusive character has often made them a topic of discussion. To shed some light on this issue, we simulate the dynamics governed by a Jahn-Teller Hamiltonian and analyze it employing two theoretical representations of the molecular wave function: the adiabatic and the exact factorization. We find fundamental differences between effects related to topological phases arising exclusively in the adiabatic representation, and thus not related to any physical observable, and geometric phases within the exact factorization that can be connected to an observable quantity. We stress that while the topological phase of the adiabatic representation is an intrinsic property of the Hamiltonian, the geometric phase of the exact factorization depends on the dynamics that the system undergoes and is connected to the circulation of the nuclear momentum field.

Herein, we have developed a new biopolymer gel electrolyte based on xanthan, a material widely used in the food and pharmaceutical industry. The incorporation of the ionic liquids 1-butyl-2,3-dimethylimidazolium iodide (BMMI.I) and 1-ethyl-2,3-dimethylimidazolium iodide (EMMI.I) has significantly enhanced ionic conductivity by 136% and 181%, respectively. These ionic liquids possess a substantial permanent dipole moment, which can induce the alignment of other dipoles around them, through conformational changes. The interplay between the ionic liquid and the segmental motion of the polymer was investigated through temperature-dependent conductivity measurements using the Vogel-Tamman-Fulcher equation. Analysis of the complex dielectric (ε′and ε″) constants revealed the polarization effect of ionic species at the electrode/electrolyte interface. Additionally, the analysis of the complex electric modulus (M′and M″) and the loss tangent (tang δ) show that the incorporation of EMMI.I resulted in an electrolyte with the shortest relaxation time, indicating greater segmental motion of the polymeric chain, ultimately leading to higher ionic conductivity. DSSCs assembled with biopolymer gel electrolytes containing ionic liquids demonstrated an improvement in the short-circuit current, which is related to the high ionic conductivity.

Newton-X is an open-source computational platform to perform nonadiabatic molecular dynamics based on surface hopping and spectrum simulations using the nuclear ensemble approach. Both are among the most common methodologies in computational chemistry for photo -physical and photochemical investigations. This paper describes the main features of these methods and how they are implemented in Newton-X. It emphasizes the newest developments, including zero-point-energy leakage correction, dynamics on complex-valued potential energy surfaces, dynamics induced by incoherent light, dynamics based on machine-learning potentials, exciton dynamics of multiple chromophores, and supervised and unsupervised machine learning techniques. Newton-X is interfaced with several third-party quantum-chemistry programs, spanning a broad spectrum of electronic structure methods.

We performed computational simulations of the photodynamics of a self-assembled monolayer (SAM) of an azobenzene derivative (azobiphenyl, ABPT) on a gold surface. An excitonic approach was adopted in a semiempirical framework, which allowed us to consider explicitly the electronic degrees of freedom of 12 azobenzene chromophores. The surface hopping scheme was used for nonadiabatic molecular dynamics simulations. According to our results for an all trans-ABPT SAM, the excitation energy transfer between different chromophores, very fast in the ππ∗ manifold, does not occur between nπ∗ states. As a consequence, the excitation transfer does not play an important role in the quenching of the azobenzene photoisomerization in the SAM (experimentally observed and reproduced by our calculations) which, instead, has to be attributed to steric effects.

We present an implementation of the Frenkel exciton model in the framework of the semiempirical floating occupation molecular orbitals-configuration interaction (FOMO-CI) electronic structure method, aimed at simulating the dynamics of multichromophoric systems, in which excitation energy transfer can occur, by a very efficient approach. The nonadiabatic molecular dynamics is here dealt with by the surface hopping method, but the implementation we proposed is compatible with other dynamical approaches. The exciton coupling is computed either exactly, within the semiempirical approximation considered, or by resorting to transition atomic charges. The validation of our implementation is carried out on the trans-azobenzeno-2S-phane (2S-TTABP), formed by two azobenzene units held together by sulfur bridges, taken as a minimal model of multichromophoric systems, in which both strong and weak exciton couplings are present.

A series of 1,3-benzoselenazole derivatives were prepared with different substituents by complementary methodologies starting from aldehydes or carboxylic acids, using sodium metabisulfite and tributylphosphine, respectively, according to the substituent pattern. The photophysical behaviour in solution of the benzoselenazoles was studied using UV-Vis absorption and steady-state fluorescence emission spectroscopies. These compounds present absorption maxima located in the UV region due to spin and symmetry, which allowed electronic transitions (1)pi pi*. The absorption maxima location, as well as the evidence of intramolecular charge transfer (ICT), was shown to be tailored by the position and electronic character of the substituents. Quantum chemical calculations using DFT and TDDFT were performed in order to investigate the electronic and photophysical features of the molecules. The calculations confirmed the presence of ICT in the molecules which contained nitro group in their structure and in all compounds where the allowed electronic transitions (1)pi pi* were taking place. In addition, the compounds showed significantly different fluorescence emissions depending on the solvent and their chemical structures, where structured and non-structured spectra in the range of 300-600 nm, with ICT character, were obtained. (C) 2020 Elsevier B.V. All rights reserved.

This work describes the synthesis and photophysical investigation of amino and azido benzazoles. The amino derivatives were obtained by condensation reaction between ortho-substituted anilines and p-aminobenzoic in polyphosphoric acid. The respective azides were synthesized by reaction of diazonium salts from the previously prepared amines with sodium azide. These compounds present absorption maxima in the UV-A region, nm ascribed to fully spin and symmetry electronic transitions. All compounds presented a main fluorescence emission in the UV-A to the violet region with a relatively large Stokes shift. The latter related to a solvent dependence. The amino derivatives presented higher values to the fluorescence quantum yields in despite of the azido analogues. DFT, TD-DFT and multiconfigurational calculations (SA-CASSCF and MS-CASPT2) were performed in order to investigate the photophysical features of these molecules, mainly on the azide derivatives, where the main interest was the investigation of the intrinsic fluorescence quenching present in these compounds. In this sense, it was observed that the weak fluorescence emission observed in the azide compounds could be related to the dissociative character of the S1 state, which reaches a conical intersection point between S1/S0 states, and through this point, goes back to the ground state by a nonradioactive decay. In addition, the DNA binding assays by UV–Vis absorption and fluorescence emission methodologies indicated that the benzazoles presented strong interaction with CT-DNA, which could be attributed to π-stacking and/or intermolecular hydrogen-bonding. Docking was also performed to better understand the observed interaction.

Lipophilic 2,1,3-benzothiadiazoles were obtained in a short synthesis with excellent yields by a Sonogashira coupling reaction followed by a 1,3-dipolar cycloaddition reaction with alkyl azides. The obtained compounds presented high solubility in a wide range of solvents with different polarities. The benzothiadiazoles present absorption in the violet region due to fully spin- and symmetry-allowed pi-pi* electronic tansitions and an emission located in the blue-green region with a large Stokes shift. The high solubility in apolar media, along with their photophysical properties allowed their use as tagging materials up to a detection limit of 0.005 ppm. Moreover, their application as chemosensors for the detection of fuel adulteration in commercial gasoline in the range of 5-50 % ethanol/gasoline (v/v) was also sucesfully presented and discussed.

The photolysis mechanisms of 1H-1,2,3-triazole and 1H-1,2,3-benzotriazole were elucidated by employing multiconfigurational methods (CASSCF and CASPT2). The potential energy curves and crossing points for the low-lying excited states were analyzed. In addition to the static electronic structure calculations, non-adiabatic molecular dynamics (NAMD) was propagated at the CASSCF level using SHARC (Surface Hopping including ARbitrary Couplings) dynamics in order to verify the proposed static picture, thereby understanding the possible reaction paths and the time scale of the photo-induced events. The S1 state for 1H-1,2,3-triazole reached a conical intersection between the S0 and S1 surfaces on a time scale of 100 fs. The emerging picture of the reaction presented here is the rupture of the triazole ring in the S1 state and the relaxation through a conical intersection to the S0 state. On the S0 surface, the triazoles easily extrude N2 and then undergo the hetero-Wolff rearrangement forming ethanimine.

The simple photolysis of CO2 in aqueous solutions to generate CO and/or hydrocarbons and derivatives in the presence of a catalyst is considered to be a clean and efficient approach for utilizing CO2 as a C1 building block. Despite the huge efforts dedicated to this transformation using either semiconductors or homogeneous catalysts, only small improvements of the catalytic activity have been achieved so far. This article reports that simple aqueous solutions of organic salts-denominated as ionic liquids-can efficiently photo-reduce CO2 to CO without using photosensitizers or sacrificial agents. The system relies on the formation of the [CO2](.-) intermediate through homolytic C-C bond cleavage in a cation-CO2 adduct of imidazolium-based ionic liquids (ILs). The system continuously produced CO up to 2.88 mmol g(-1) of IL after 40 h of irradiation by using an aqueous solution of 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIm.CO2) IL, representing an apparent quantum yield of 3.9 %. The organophotocatalytic principles of our system may help to develop more simple and efficient organic materials for the production of solar fuels from CO2 under mild conditions, which represents a real alternative to those based on semiconductors and homogeneous metal-based catalysts.

In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles.

This study involves the electrochemical, thermal and photophysical profiling of new pyromellitic diimide (PMDI) derivatives containing alkyl chains of different sizes. The photophysical investigation shows that all compounds exhibited absorption in the UV-B region (similar to 290 nm). The band-gaps were calculated by onset peak values of around 4.03 eV. The compounds are photoactive in the UV-A region (312-328 nm) with a small solvatochromic effect in the excited state (Delta lambda(em) = 16 nm). The electrochemical studies revealed that the reduction of the bisimide moiety showed two waves due to the formation of both the radical anion and a dianion. On the other hand, oxidation showed two waves due to the formation of radical cations and dications. The thermal properties were measured by differential thermal analysis (DTA) and thermogravimetric analysis (TGA), and the materials showed high thermal stability (T-d > 300 degrees C). Theoretical calculations were also performed to study the geometry and charge distribution of these compounds in their ground and excited electronic states. No significant changes in the absorption and emission maxima were found by changing the solvent or substituents attached to the PMDI structure.