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DFT functionals are tested against CCSD(T) for the calculation of EFGs, and applied to model systems of the CueR metal site. Large model systems are required for accurate results. Nuclear decay of Ag(i) to Cd(ii) leads to distortion of the metal site.

Helicenes are of general interest due to the significant chiral signals in both absorption- and emission-based spectroscopy. Herein, the spectroscopic properties of four recently synthesized azaoxahelicenes are studied using density functional theory methods. The azaoxahelicenes have 7, 9, 10, and 13 units and one to two complete turns of the structure. UV-vis absorption and electronic circular dichroism spectra are determined both in vacuum and in solution using explicit solvation through a combined molecular dynamics/polarizable embedding framework. Additionally, emission and circularly polarized luminescence spectra are determined based on vibronic calculations. The resulting spectra are in good agreement with the experimentally available data, highlighting that both absorption- and emission-based spectra of the systems can be modeled computationally such that reliable predictions can be made for systems that are yet to be synthesized.

Experimental studies show large isotope-dependent effects in the photolysis rates of formaldehyde isotopologues, that are both wavelength and pressure dependent. These effects are on the order of 10-20% for 13C and 18O (L. Feilberg et. al, J. Phys. Chem. A, 109, 8314-8319, 2004), and 60% for CHDO (E. J. K Nilsson et. al, ACP, 14, 551–558, 2014). We have made a model of the elementary processes involved in the photodissociation including unimolecular dissociation, collisional quenching and crossing between excited state surfaces. Computational chemistry is used to characterize some of these processes. The model is validated by comparison to all existing experimental data and is then used to make predictions about the isotopic fractionation in additional isotopicules (and for conditions not yet addressed by experiment) including fractionation in clumped molecules. The following isotopologues of formaldehyde have been investigated; HCHO, DCHO, DCDO, D13CHO, H13CHO, HCH17O, HCH18O, H13CH17O and H13CH18O. Rice–Ramsperger–Kassel–Marcus (RRKM) theory was used to calculate the rates for decomposition of the S0, S1 and T1 states with CCSD(T)/aug-cc-pVTZ, ωB97X-D/aug-cc-pVTZ and CASPT2/aug-cc-pVTZ levels of theory. Furthermore, the rates and likelihood of intersystem crossing were investigated by including the spin-orbit coupling between the excited states. The model was able to replicate the experimental pressure trends accurately, however, the kinetic isotope effect was one order of magnitude too small for the non-deuterated isotopologues. We predict a large clumped isotope anomaly in 13C18O produced by formaldehyde photolysis.

Herein, we present an investigation of the excited state dynamics of the dihydroazulene photoswitch and its photoinduced reaction to vinylheptafulvene. The focus is on how the introduction of a benzannulated ring in different sites of the structure can modify the excited state topology and thus the kinetics of the ring opening reaction of DHA by alteration of the excited state conjugation of the system. The dynamics of the systems is obtained utilizing

In this paper, we present an investigation concerning the prospects of using nanoparticles to improve solar energy storage properties of three different norbornadiene/quadricyclane derivatives. Computationally, we study how different nanoparticles influence the properties of the systems that relate to the storage of solar energy, namely, the storage energy and the back reaction barrier. Our approach employs hybrid quantum mechanical/molecular mechanical calculations in which the molecular systems are described using density functional theory while the nanoparticles are described using molecular mechanics. The interactions between the two subsystems are determined using polarization dynamics. The results show that the influence of the nanoparticles on the thermochemical properties largely depends on the type of nanoparticle used, the relative orientation with respect to the nanoparticle, and the distance between the the nanoparticle and the molecular system. Additionally, we find indications that copper and/or titanium dioxide nanoparticles can lower the energy barrier of the back reaction for all of the studied systems without significantly lowering the storage capability of the systems. Consequently, the study shows that nanoparticles can potentially be employed in the optimization of molecular photoswitches towards solar energy storage.

A boron subphthalocyanine molecule has been employed as a novel electron donor in organic solar cells (OPVs), and optimized in terms of composition and device structure in small molecule solar cells. It is demonstrated that the power conversion efficiency (PCE) of the devices obtained by solution-processing in bulk heterojunction solar cells could be improved by one order of magnitude by changing the fabrication method to vacuum deposition, which promotes a better morphology in the OPV active layers. Importantly, upon insertion of an additional pristine C70 thin interlayer between the active layer and the hole transport layer the PCE was further improved, highlighting the importance of interfacial layer engineering in such subphthalocyanine small molecule OPVs.

The nuclear quadrupole interaction (NQI) of quadrupolar nuclei in molecules in the gas phase has recently been quantified experimentally by the technique of Perturbed Angular Correlation (PAC) spectroscopy. Interpretation of the NQI data must rely on high-level electronic structure methods for the calculation of the electric field gradient (EFG). These calculations commonly omit contributions from anharmonicity, rovibrational coupling and (if applicable) decay-induced nuclear recoil to the molecular structure and the response of the EFG. Here we choose an alternative approach, conducting Born-Oppenheimer molecular dynamics (BOMD) simulations, and account for the effects of molecular motion on the EFG. We apply this approach to the analysis of PAC spectroscopic data recorded for gas phase CdI2 (Haas et al., 2021). With this methodology, we obtain a value of the nuclear quadrupole moment Q(Cd-111, 5/2(+)) = 0.656(7) b.

Polycyclic aromatic hydrocarbons (PAHs) have found strong interest for their electronic properties and as model systems for graphene. While PAHs have been studied intensively as single units, here PAHs were constructed in ladder-type arrangements using cross-conjugated fulvalene and dithiafulvalene motifs as connecting units and moving forward a convenient synthetic approach for dimerizing (thio)ketones into olefins by the action of Lawesson's reagent. Some of the PAHs can also be regarded as "super-extended" tetrathiafulvalenes (TTFs) with some of the largest cores ever explored, being multi-redox systems that exhibit both reversible oxidations and reductions. Concomitant absorption redshifts were observed when expanding the ladder-type structures from one to two to three indenofluorene units, and optical and electrochemical HOMO-LUMO gaps were found to correlate linearly. Various conformations (and solid-state packing arrangements) were studied by X-ray crystallography and computations.

The convergence of the recently developed cluster perturbation (CP) expansions [Pawlowski et al., J. Chem. Phys. 150, 134108 (2019)] is analyzed with the double purpose of developing the mathematical tools and concepts needed to describe these expansions at general order and to identify the factors that define the rate of convergence of CP series. To this end, the CP energy, amplitude, and Lagrangian multiplier equations as a function of the perturbation strength are developed. By determining the critical points, defined as the perturbation strengths for which the Jacobian becomes singular, the rate of convergence and the intruder and critical states are determined for five small molecules: BH, CO, H2O, NH3, and HF. To describe the patterns of convergence for these expansions at orders lower than the high-order asymptotic limit, a model is developed where the perturbation corrections arise from two critical points. It is shown that this model allows for rationalization of the behavior of the perturbation corrections at much lower order than required for the onset of the asymptotic convergence. For the H2O, CO, and HF molecules, the pattern and rate of convergence are defined by critical states where the Fock-operator underestimates the excitation energies, whereas the pattern and rate of convergence for BH are defined by critical states where the Fock-operator overestimates the excitation energy. For the NH3 molecule, both forms of critical points are required to describe the convergence behavior up to at least order 25.

We have extended cluster perturbation (CP) theory to comprehend the calculation of first order properties (FOPs). We have determined CP FOP series where FOPs are determined as a first energy derivative and also where the FOPs are determined as a generalized expectation value of the external perturbation operator over the coupled cluster state and its biorthonormal multiplier state. For S(D) orbital excitation spaces, we find that the CP series for FOPs that are determined as a first derivative, in general, in second order have errors of a few percent in the singles and doubles correlation contribution relative to the targeted coupled cluster (CC) results. For a SD(T) orbital excitation space, we find that the CP series for FOPs determined as a generalized expectation value in second order have errors of about ten percent in the triples correlation contribution relative to the targeted CC results. These second order models, therefore, constitute viable alternatives for determining high quality FOPs.

Chemical process design has for long been benefiting from computer-aided methods and tools to develop new processes and services that can meet the needs of society. Chemical and biomolecular product design could also benefit from the use of computer-aided solution strategies and computational power to efficiently solve the problems at various scales as the complexity and size of problems grow. In this context, new modes of computation such as quantum computing are receiving increasing attention. While quantum computing has been in development for quite some time, the development of the technology to the point of making commercial use of such resources is quite recent, and still quite limited in scope. However, projections point to a rapid development of quantum computing resources becoming available to academia and industry, which opens potential application areas in chemical and biomolecular product design. With the advent of hybrid algorithms that are able to take advantage of both classical computing and quantum computing resources, as quantum computing grows, more and more problems relevant for chemical product design will become solvable. In this paper, some perspectives are given by identifying a set of needs and challenges for a selected set of opportunities, such as quantum chemistry-based property prediction, protein folding, complex multi-step chemical reactions, and molecular reaction dynamics.

This paper investigates the electric properties of the photochromic dihydroazulene/vinylheptafulvene system as it is physisorbed onto silver and copper nanoparticles. Our focus is on how the polarizability and hyperpolarizability of the dihydroazulene, s

In the gas phase, formaldehyde has an electric-dipole forbidden transition that becomes allowed by vibronic coupling. In this paper we explore whether perturbation by surfaces could also enhance light absorption by CH

We investigate the effects of nanoparticles on molecular solar thermal energy storage systems and how one can tune chemical reactivities of a molecular photo- and thermoswitch by changing the nanoparticles. We have selected the dihydroazulene/vinylheptafulvene system to illustrate the effects of the nanoparticles on the chemical reactivities of the molecular photo- and thermoswitch. We have utilized the following nanoparticles: a TiO2 nanoparticle along with nanoparticles of gold, silver and copper. We calculate the rate constants for the release of the thermal energy utilizing a QM/MM method coupled to a transition state method. The molecular systems are described by density functional theory whereas the nanoparticles are given by molecular mechanics including electrostatic and polarization dynamics. In order to investigate whether the significant stabilization of the transitions state provided by the nanoparticles is general to the DHA/VHF system, we calculated the transition state rate constant of the parent- and 3-amino-substituted-DHA/VHF systems at 298.15 K in the four different orientations and at the three different separations. We observe that the transition state rate constant of the parent system is only increased as the cyano groups are oriented towards the nanoparticle while the presence of the nanoparticle actually impedes the reactions using the three other orientations. On the other hand, for the substituted system the nanoparticle generally leads to a significant increase in the rate of the reaction. We find that the nanoparticles can have a substantial effect on the calculated rate constants. We observe, depending on the nanoparticle and the molecular orientation, increases of the rate constants by a factor of 106. This illustrates the prospects of utilizing nanoparticles for controlling the release of the stored thermal energy.

Molecular photoswitches based on the norbornadiene–quadricylane (NBD–QC) couple have been proposed as key elements of molecular solar thermal energy storage schemes. To characterize the intrinsic properties of such systems, reversible isomerization of a charge-tagged NBD–QC carboxylate couple is investigated in a tandem ion mobility mass spectrometer, using light to induce intramolecular [2 + 2] cycloaddition of NBD carboxylate to form the QC carboxylate and driving the back reaction with molecular collisions. The NBD carboxylate photoisomerization action spectrum recorded by monitoring the QC carboxylate photoisomer extends from 290 to 360 nm with a maximum at 315 nm, and in the longer wavelength region resembles the NBD carboxylate absorption spectrum recorded in solution. Key structural and photochemical properties of the NBD–QC carboxylate system, including the gas-phase absorption spectrum and the energy storage capacity, are determined through computational studies using density functional theory.

Sampling the shallow free energy surface of hydrated atmospheric molecular clusters is a significant challenge. Using computational methods, we present an efficient approach to obtain minimum free energy structures for large hydrated clusters of atmospheric relevance. We study clusters consisting of two to four sulfuric acid (sa) molecules and hydrate them with up to five water (w) molecules. The structures of the "dry" clusters are obtained using the ABCluster program to yield a large pool of low-lying conformer minima with respect to free energy. The conformers (up to ten) lowest in free energy are then hydrated using our recently developed systematic hydrate sampling technique. Using this approach, we identify a total of 1145 unique (sa)(2-4)(w)(1-5) cluster structures. The cluster geometries and thermochemical parameters are calculated at the omega B97X-D/6-31++G(d,p) level of theory, at 298.15 K and 1 atm. The single-point energy of the most stable clusters is calculated using a high-level DLPNO-CCSD(T-0)/aug-cc-pVTZ method. Using the thermochemical data, we calculate the equilibrium hydrate distribution of the clusters under atmospheric conditions and find that the larger (sa)(3) and (sa)(4) clusters are significantly more hydrated than the smaller (sa)(2) cluster or the sulfuric acid (sa)(1) molecule. These findings indicate that more than five water molecules might be required to fully saturate the sulfuric acid clusters with water under atmospheric conditions. The presented methodology gives modelers a tool to take the effect of water explicitly into account in atmospheric particle formation models based on quantum chemistry.

Dihydroazulene (DHA) is a molecular photoswitch that undergoes a ring-opening reaction upon irradiation to form a vinylheptafulvene (VHF) photoisomer. This VHF isomer will in time thermally return to the DHA isomer. As the isomerization is photo-induced only in one direction, the DHA – VHF couple has attracted interest as a molecular solar thermal energy storage device (MOST system). In this author review, we cover our systematic efforts to optimize the DHA – VHF couple for this purpose, with challenges being to achieve sufficiently high energy densities, to cover broad absorptions including the visible region, and to control the energy-releasing VHF-to-DHA back-reaction. By a combination of computations and experiments, we review the consequences of various structural modifications of the system (structure – property relationships), including the influence of donor-acceptor substitution at specific positions, benzannulations, and incorporation into macrocyclic structures. Synthetic protocols to reach the various modifications will also be discussed. The bibliography includes 60 references.

Organic photovoltaic devices are promising candidates for efficient energy harvesting from sunlight. Designing new dye molecules suitable for such devices is a challenging task restricted by the rapid increase of computational cost with system size. Solar cell material properties are closely related to the electronic structure of the dye, and an effective molecular orbital energy screening method for a family of dyes is therefore desired. In this work, a machine learning approach is used to sort through the chemical space of peripheral double-substituted boron-Subphthalocyanine dyes. A database of 12,102 PM6 optimized structures was built and for each of the structures time-dependent density functional theory (LC-[Formula: see text]HPBE/6-31+G(d)) calculations were performed. We investigated the changes of the molecular orbital energies of the molecular orbitals related to reduction and oxidation of the compounds. With the Electrotopological-state index moleculear representation all the tested algorithms, Support Vector Machine, Random Forest Regression, Neural Network, and Simple Linear Regression, captured the calculated frontier orbital energies with a prediction root-mean-square-error in the order of 0.05 eV. Finally, frontier orbital energies were predicted for more than 40,000 new structures by the trained Support Vector Machine algorithm. Compared to the parent boron-Subphthalocyanine structure, 237 and 132 functionalized dyes were predicted to have upshifted molecular orbital energies using the Electrotopological-state index and OneHot encoding feature vector, respectively. Out of 27 investigated donor and acceptor ligands, the acetamide and hydroxyl ligands gave rise to the desired increase in frontier molecular orbital energy.

The dihydroazulene/vinylheptafulvene (DHA/VHF) photocouple is a promising candidate for molecular solar heat batteries, storing and releasing energy in a closed cycle. Much work has been done on improving the energy storage capacity and the half-life of the high-energy isomer via substituent functionalization, but similarly important is keeping these improved properties in common polar solvents, along with being soluble in these, which is tied to the dipole properties. However, the number of possible derivatives makes an overview of this combinatorial space impossible both for experimental work and traditional computational chemistry. Due to the time-consuming nature of running many thousands of computations, we look to machine learning, which bears the advantage that once a model has been trained, it can be used to rapidly estimate approximate values for the given system. Applying a convolutional neural network, we show that it is possible to reach good agreement with traditional computations on a scale that allows us to rapidly screen tens of thousands of the DHA/VHF photocouple, eliminating bad candidates and allowing computational resources to be directed toward meaningful compounds.

We present here a massively parallel implementation of the recently developed CPS(D-3) excitation energy model that is based on cluster perturbation theory. The new algorithm extends the one developed in Baudin et al. [J. Chem. Phys., 150, 134110 (2019)] to leverage multiple nodes and utilize graphical processing units for the acceleration of heavy tensor contractions. Furthermore, we show that the extended algorithm scales efficiently with increasing amounts of computational resources and that the developed code enables CPS(D-3) excitation energy calculations on large molecular systems with a low time-to-solution. More specifically, calculations on systems with over 100 atoms and 1000 basis functions are possible in a few hours of wall clock time. This establishes CPS(D-3) excitation energies as a computationally efficient alternative to those obtained from the coupled-cluster singles and doubles model.

In this article, a modification of the second-order polarization propagator approximation (SOPPA) method is introduced and illustrated for the calculation of the indirect nuclear spin–spin couplings. The standard SOPPA method, although cheaper in terms of computational cost, offers less accurate results than the ones obtained with coupled cluster methods. A new method, named SOPPA+A3-3, was therefore developed by adding the terms of the third-order A matrix that rely on the second-order double amplitudes. The performance of this third-order contribution was studied using the coupled cluster singles and doubles method as a reference, calculating the spin–spin couplings of molecules of diverse sizes and compositions, and comparing them to the SOPPA method. The results show that inclusion of this third-order contribution gives more accurate results than the standard SOPPA method with a level of accuracy close to that of the coupled cluster method with only a small increase in the computational cost of the response calculation that dominates the computational cost for small- to medium-sized molecules. The implementation of the first contributions to the third-order polarization propagator approximation in the Dalton program, thus, already shows a significant change in these molecular properties over those obtained with the standard SOPPA method.

Molecular solar-thermal energy storage (MOST) systems are based on photoswitches that reversibly convert solar energy into chemical energy. In this context, bicyclooctadienes (BODs) undergo a photoinduced transformation to the corresponding higher energy tetracyclooctanes (TCOs), but the photoswitch system has not until now been evaluated for MOST application, due to the short half-life of the TCO form and limited available synthetic methods. The BOD system degrades at higher temperature via a retro-Diels-Alder reaction, which complicates the synthesis of the compounds. We here report a cross-coupling reaction strategy that enables an efficient synthesis of a series of 4 new BOD compounds. We show that the BODs were able to switch to the corresponding tetracyclooctanes (TCOs) in a reversible way and can be cycled 645 times with only 0.01% degradation. Half-lives of the TCOs were measured, and we illustrate how the half-life could be engineered from seconds to minutes by molecular structure design. A density functional theory (DFT) based modelling framework was developed to access absorption spectra, thermal half-lives, and storage energies which were calculated to be 143-153 kJ mol-1 (0.47-0.51 MJ kg-1), up to 76% higher than for the corresponding norbornadiene. The combined computational and experimental findings provide a reliable way of designing future BOD/TCO systems with tailored properties., The project made use of the NMR Uppsala infrastructure, which is funded by the Department of Chemistry-BMC and the Disciplinary Domain of Medicine and Pharmacy. The authors would like to thank the Knut & Alice Wallenberg Foundation, The Swedish Research Council FORMAS, the Swedish Energy Agency, The Swedish Research Council (Vetenskapsrådet) and the European Union's Horizon 2020 Framework Programme under grant agreement number 951801 for financial support., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

We present linear optical absorptions of photo/thermochromic molecules interacting with a gold nanoparticle. The photo/thermochromic system is the dihydroazulene/vinylheptafulvene (DHA/VHF) system and our aim is to study the effects of the interaction between the gold nanoparticle and the molecular systems. We consider the changes of the one-photon excitations of the dihydroazulene/vinylheptafulvene system as we increase the interactions between the molecules and the nanoparticle by decreasing the distance between them. We utilize a quantum mechanical/molecular mechanical method for investigating the photo/thermochromic molecular system interacting with the gold nanoparticle. The photo/thermochromic molecules are described quantum mechanically using density functional theory whereas the gold nanoparticle is represented as gold atoms with atomic polarizabillities using molecular mechanics. We observed that the optical properties of the photo/thermochromic systems are affected by the presence of the nanoparticle and the changes depend strongly on the conformer of the molecular system along with the relative orientation and distance between the photo/thermochromic molecules and the nanoparticle.

Molecular photoswitches can under certain conditions be used to store solar energy in the so-called molecular solar thermal storage systems, which is an interesting technology for renewable energy solutions. The current investigations focus on the performance of seven different density functional theory (DFT) methods (B3LYP, CAM-B3LYP, PBE0, M06-2X, ωB97X-D, B2PLYP, and PBE0DH) when predicting geometries and thermochemical properties of the [2.2.2]-bicyclooctadiene (BOD) photoswitch. We find that all of the investigated DFT methods provide geometries that are in good agreement with those obtained using coupled cluster singles and doubles (CCSD) calculations. The dependence on the employed basis set is not large when predicting geometries. With respect to the thermochemical properties, we find that the M06-2X, CAM-B3LYP, PBE0, and ωB97X-D functionals all predict thermochemical properties that are in good agreement with the results of the CCSD, the CCSD including perturbative triples (CCSD(T)), and the explicitly correlated CCSD-F12 and CCSD(T)-F12 models. Lastly, for energy calculations, we tested the newly developed fourth-order cluster perturbation theory singles and doubles CPS(D-4) model, which in this study provides energy differences that are of CCSD and sometimes also CCSD(T) quality at a relatively low cost. We find that the CPS(D-4) model is an excellent choice for further investigation of BOD derivatives because accurate energies can be obtained routinely using this methodology. From the results, we also note that the predicted storage energies and storage energy densities for the BOD photoswitch are very large compared to other molecular solar thermal storage systems and that these systems could be candidates for such applications., The authors thank the European Union’s Horizon 2020 Framework Programme under grant agreement number 951801 for financial support. The authors would also like to thank the financial support from K. & A. Wallenberg foundation, the Swedish Foundation for Strategic Research, the Swedish research foundation FORMAS, and the Swedish Energy Agency., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

We present a computational methodology for the screening of a chemical space of 10²⁵ substituted norbornadiene molecules for promising kinetically stable molecular solar thermal (MOST) energy storage systems with high energy densities that absorb in the visible part of the solar spectrum. We use semiempirical tight-binding methods to construct a dataset of nearly 34,000 molecules and train graph convolutional networks to predict energy densities, kinetic stability, and absorption spectra and then use the models together with a genetic algorithm to search the chemical space for promising MOST energy storage systems. We identify 15 kinetically stable molecules, five of which have energy densities greater than 0.45 MJ/kg and the main conclusion of this study is that the largest energy density that can be obtained for a single norbornadiene moiety with the substituents considered here, while maintaining a long half-life and absorption in the visible spectrum, is around 0.55 MJ/kg.

The kinetic recoil energy received by the daughter nucleus in a nuclear decay is often large enough to affect the structure around the nucleus in chemical systems. The coinciding element change which typically occurs in a nuclear decay may additionally incur a structural reorganization. The effects of these phenomena on chemical systems where radio-isotopes are used are often little-known or neglected because the dynamics of nuclear decay is difficult to observe experimentally. In this work, QM-MD simulations are used to investigate local fs to ps dynamics following the β-decay of 111Ag to 111Cd in systems modelled on the metal-sensing CueR protein. An adiabatic approximation is applied, assuming that the electronic structure relaxes rapidly after the decay. PM7-MD simulations of recoil dynamics of the model systems show significant structural changes and bonding interactions that depend on the magnitude and direction of the recoil. We find that, in general, the kinetic recoil energy is rapidly distributed (

Inthis work, we focus on macrocyclic structures comprised of two dihydroazulene (DHA) units and one azobenzene (AZB) unit and the possibility for photoisomerizing one unit selectively by tuning the excitation energies of each individual unit. An unfortunate overlap between the absorption bands of DHA and AZB as well as trans-and cis-AZB prevents us to have a full control onthese macrocyclic structures, and their absorption bands need to be separated. By means of time-dependent density-functional theory calculations, we investigate the effects of ortho substitutions of the AZB unitby fluorine and chlorine atoms on the absorption spectra of the DHA/AZB macrocycles. The calculations on the isolated AZB show that substitutions lead to distortion of the planar molecular structure because of the repulsive interactions between halogen atoms and a systematic blueshift of the ππ* bands between 25 and 50 nm. Moreover, separations between 10 and 48 nm, depending on the substituent, are observed in the nπ* bands. The results from the calculations on the substituted AZB–DHA–DHA macrocycles reveal significant separations of the DHA/trans-AZB and trans-/cis-AZB absorption bands by values of 46–73 and 15–52 nm, respectively, for different substitutions. We realize that ortho substitutions with mixed fluorine–chlorine-atoms can provide the best separations in both ππ* and nπ* bands of AZB–DHA–DHA photoisomers. The results of this work offer a guideline for designing and synthesizing new, efficient, and highly controllable materials applicable in devices for optical data storage and molecular electronics.

The loss of a Cl atom from metastable CH2Cl2+ in the mass-analyzed ion kinetic energy experiment is characterized by a borderline zero kinetic energy release and large kinetic isotope effects on chlorine and hydrogen. Ab initio calculations are employed to assist the interpretation in terms of a nonadiabatic reaction involving electronic predissociation of the electronically excited state 2A1 and two-dimensional reaction dynamics. Strong curvature in the reaction coordinate leads to a bobsled effect that accounts for the low kinetic energy release. The kinetic isotope effects enter via the predissociation rate and are interpreted in terms of vibrational overlap integrals.

We present an efficient approach for estimating the construction of molecular solar thermal systems in the context of hybrid solar thermal devices. Photochromic molecules can store thermal energy by structural changes, and the storage time depends on the chosen molecular system and temperature. The simulation framework can predict thermal energy storage rates, conversion percentages, and temperature increases. The model is based on both microscopic and macroscopic properties, which all have an impact on the energy storage efficiency. The microscopic parameters include the molecular storage energies, the quantum yield for the photoisomerization, the absorption properties for the photochromic molecule, and the lifetime of the metastable molecule, hence the possible storage time. The macroscopic parameters of the hybrid device include engineering specifications like the device dimensions, device material, the solar concentration factor, the flow rate of the fluid, and the start concentration of the photochromic molecule.

Theoretical calculations involving singlet molecular oxygen (O2(1g)) are challeng- ing due to their inherent multi-reference character. We have tested the quality of re- stricted and unrestricted DFT geometries obtained for the reaction between singlet oxy- gen and a series of alkenes (propene, 2-methylpropene, trans-butene, 2-methylbutene and 2,3-dimethylbutene) which are able to follow the ene-reaction. The electronic en- ergy of the obtained geometries are rened using 3 dierent methods which account for the multi-reference character of singlet oxygen. The results show that the mechanism for the ene-reaction is qualitatively dierent when either one or two allylic-hydrogen groups are available for the reaction. When one allylic-hydrogen group is available the UDFT calculations predict a stepwise addition forming a biradical intermediate, while, the RDFT calculations predict a concerted reaction where both hydrogen abstrac- tion and oxygen addition occur simultaneously. When two allylic-hydrogen groups are available for the reaction then UDFT and RDFT predict the same reaction mechanism, namely that the reaction occurs as a stepwise addition without a stable intermediate between the two transition states. The calculated rate constants are in reasonable agreement with experimental data, except for trans-butene where the calculated rate constant is three orders of magnitude lower than the experimental one. In conclusion we nd that the simple bypassing scheme tested in this paper is a robust approach for calculations of reaction involving singlet oxygen in the limit that the transition state processes low multi-reference character. 2

The synthesis path of the C60-Buckyball fullerene from a planar precursor developed by Scott et al. [Science, 2002, 295, 5559] is investigated with density functional theory (DFT) methods. Various theoretically possible closing paths are analysed with respect to structural and energetic properties. The initial geometries were obtained by geometric interpolation of a cardboard-like model comprising rigid rings connected by hinges, which were then fully optimized with a selection of DFT-functionals. Analysis of the fully optimised geometries shows remarkable stability of face planarity, bond lengths and bond angles for all studied geometries, indicating soundness of the “cardboard with hinges”-model for approximating reaction paths for molecules of this type. This raises hope for development of a force field description of fullerene precursor molecules that can aid in discovery and analysis of good precursor candidates for rational synthesis of new fullerenes.

We have extended cluster perturbation (CP) theory to comprehend the Lagrangian framework of coupled cluster (CC) theory and derived the CP Lagrangian energy series ( L CP) where the 2 n + 1/2 n + 2 rules for the cluster amplitudes and multipliers are used to get the energy corrections. We have also developed the variational CP [Formula: see text] series, where the total cluster amplitudes and multipliers are determined through the same orders as in the L CP series, but the energy is obtained by inserting the total cluster amplitudes and multipliers in the Lagrangian. The energies of the [Formula: see text] series have errors that are bilinear in the errors of the total cluster amplitudes and multipliers. Test calculations have been performed for S(D) and SD(T) orbital excitation spaces. With the exception of molecular systems that have a low lying doubly excited state compared to the electronic ground state configuration, we find that the fourth order models [Formula: see text]( D−4), [Formula: see text]( T−4), and L CPSD( T−4) give energies of CC target state quality. For the [Formula: see text]( D−4) model, CC target state quality is obtained as the [Formula: see text]( D−4) calculation determines more than 99.7% of the coupled cluster singles and doubles (CCSD) correlation energy as the numerical deviations of the [Formula: see text]( D−4) energy from the CCSD energy were more than an order of magnitude smaller than the triples correlation contribution. For the [Formula: see text]( T−4) and L CPSD( T−4) models, CC target state quality was obtained, given that the [Formula: see text]( T−4) and L CPSD( T−4) calculations recover more than 99% of the coupled cluster singles doubles and triples (CCSDT) correlation contribution and as the numerical deviations of the [Formula: see text]( T−4) and L CPSD( T−4) energies from the CCSDT energy were nearly and order of magnitude smaller than the quadruples correlation contribution. We, thus, suggest that the fourth order models may replace the full target CC models with no or very limited loss of accuracy.

We present a detailed theoretical study of the electronic absorption spectra and thermochemistry of molecular photoswitches composed of one and two photochromic units of dihydroazulene (DHA)/vinylheptafulvene (VHF) molecules. Six different isomers are considered depending on the ring opening/closure forms of the DHA units. The solvent effect of acetonitrile is investigated using a sequential Molecular Mechanics/Quantum Mechanics approach. The thermochemical investigations of these photochromic molecules were performed using the Free Energy Perturbation method, and the simulations were performed using Configurational Bias Monte Carlo. We show that to open the 5-member ring of the DHA, there is no significant gain in thermal release of energy for the back reaction when a unit or two DHA units are considered. Overall, we found agreement between the solvation free energy based on Monte Carlo simulations and the continuum solvent model. However, the cavitation term in the continuum model is shown to be a source of disagreement when the non-electrostatic terms are compared. The electronic absorption spectra are calculated using TDDFT CAM-B3LYP/cc-pVDZ. Agreement with experiment is obtained within 0.1 eV, considering statistically uncorrelated configurations from the simulations. Inhomogeneous broadening is also considered and found to be well described in all cases.

Photoswitch triads comprising two dihydroazulene (DHA) units in conjugation with a central trans-azobenzene (AZB) unit were prepared in stepwise protocols starting from meta- and para-disubstituted azobenzenes. The para-connected triad had significantly altered optical properties and lacked the photoactivity of the separate photochromes. In contrast, for the meta-connected triad, all three photochromes could be photoisomerized to generate an isomer with two vinylheptafulvene (VHF) units and a cis-azobenzene unit. Ultrafast spectroscopy of the photoisomerizations revealed a fast DHA-to-VHF photoisomerization and a slower trans-to-cis AZB photoisomerization. This meta triad underwent thermal VHF-to-DHA back-conversion with a similar rate of all VHFs, independent of the identity of the neighboring units, and in parallel thermal cis-to-trans AZB conversion. The experimental observations were supported by computation (excitation spectra and orbital analysis of the transitions).