The recent re‐parametrization of the Martini coarse‐grained force field, Martini 3, improved the accuracy of the model in predicting molecular packing and interactions in molecular dynamics simulations. Here, we describe how small molecules can be accurately parametrized within the Martini 3 framework and present a database of validated small molecule models. We pay particular attention to the description of aliphatic and aromatic ring‐like structures, which are ubiquitous in small molecules such as solvents and drugs or in building blocks constituting macromolecules such as proteins and synthetic polymers. In Martini 3, ring‐like structures are described by models that use higher resolution coarse‐grained particles (small and tiny particles). As such, the present database constitutes one of the cornerstones of the calibration of the new Martini 3 small and tiny particle sizes. The models show excellent partitioning behavior and solvent properties. Miscibility trends between different bulk phases are also captured, completing the set of thermodynamic properties considered during the parametrization. We also show how the new bead sizes allow for a good representation of molecular volume, which translates into better structural properties such as stacking distances. We further present design strategies to build Martini 3 models for small molecules of increased complexity.

Organic solar cells have recently experienced a substantial leap in power conversion efficiency, in part driven by formulations with new non-fullerene acceptors. This has brought the technology past the psychologically important mark of 15% efficiency for unscaled laboratory devices, and the results are stimulating another burst of research activity. Whether this will propel the technology into a viable commercial contender has yet to be determined, but to realize the potential of organic solar cells for utility scale application, fabrication using scalable processing techniques has to be demonstrated—otherwise, the passing of the 15% mark will eventually leave no more lasting impact than what the passing of the 10% mark did. Thus, addressing the scaling lag between the 15% cell efficiencies of lab-scale devices on rigid glass substrates fabricated using non-scalable techniques and the 7% efficiencies of scalably fabricated devices on flexible substrates is key. Here, we discuss the concept of scalability and give an account of the literature on non-fullerene acceptor devices fabricated with scalable methods and materials. On the basis of this, we identify three crucial focus points for overcoming the lab-to-fab challenge: (i) dual temperature control, i.e. simultaneous control of the ink and substrate temperatures during deposition, (ii) systematic in situ morphology studies of active layer inks with new, green solvent formulations during continuous deposition, and (iii) development of protocols for continuous solution processing of smooth, transparent interfacial layers with efficient charge transfer to the active layer. Combining these efforts and in general accompanying such studies with stability analyses and fabrication of large-area, scalably processed devices are believed to accelerate the relevance of organic solar cells for large-scale energy supply.

Photochemical conversion of molecules into high-energy isomers that, after a stimulus, return to the original isomer presents a closed-cycle of light-harvesting, energy storage, and release. One challenge is to achieve a sufficiently high energy storage capacity. Here, we present efforts to tune the dihydroazulene/vinylheptafulvene (DHA/VHF) couple through loss/gain of aromaticity. Two derivatives were prepared, one with aromatic stabilization of DHA and the second of VHF. The consequences for the switching properties were elucidated. For the first type, sigmatropic rearrangements of DHA occurred upon irradiation. Formation of a VHF complex could be induced by a Lewis acid, but addition of H2 O resulted in immediate regeneration of DHA. For the second type, the VHF was too stable to convert into DHA. Calculations support the results and provide new targets. We predict that by removing one of the two CN groups at C-1 of the aromatic DHA, the heat storage capacity will be further increased, as will the life-time of the VHF. Calculations also reveal that a CN group at the fulvene ring retards the back-reaction, and we show synthetically that it can be introduced regioselectively.

The recent re-parametrization of the Martini coarse-grained force field, Martini 3, improved the accuracy of the model in predicting molecular packing and interactions in molecular dynamics simulations. Here, we describe how small molecules can be accurately parametrized within the Martini 3 framework and present a database of validated small molecule models (available at https://github.com/ricalessandri/ Martini3-small-molecules and http://cgmartini.nl). We pay particular attention to the description of aliphatic and aromatic ring-like structures, which are ubiquitous in small molecules such as solvents and drugs or in building blocks constituting macromolecules such as proteins and synthetic polymers. In Martini 3, ring-like structures are described by models that use higher resolution coarse-grained particles (small and tiny particles). As such, the present database constitutes one of the cornerstones of the calibration of the new Martini 3 small and tiny particle sizes. The models show excellent partitioning behavior and solvent properties. Miscibility trends between different bulk phases are also captured, completing the set of thermodynamic properties considered during the parametrization. We also show how the new bead sizes allow for a good representation of molecular volume, which translates into better structural properties such as stacking distances. We further present design strategies to build Martini 3 models for small molecules of increased complexity. The present database, along with the outlined design strategies and the modularity of the Martini force field, constitute a resource of models that 1) can be used “as is” in (bio)molecular simulations; 2) gives reference points for the construction of other small molecule models; 3) provides guidelines and reference data for automated topology builders; and 4) can be used as building blocks for the construction of more complex (macro)molecules, hence enabling investigations of complex biomolecular and soft material systems.

The gain and loss of aromaticity plays a key role in organic chemistry and in the prediction of rate-determining steps. Herein, we explore the concept of aromaticity in photoisomerization reactions. Benzannulated derivatives of the dihydroazulene-vinylheptafulvene (DHA-VHF) photoswitch were investigated using transient absorption spectroscopy and timedependent density functional theory to elucidate the effect of built-in aromaticity on the switching properties. We found that benzannulation hampered the switching ability by enhancing an already existing barrier on the excited state surface. This enhancement was found to arise from a significant loss of aromaticity in the DHA-to-VHF transition state on the excited state potential energy surface. The VHF was found to be highly aromatic on the excited state surface, showing a reversal of aromaticity compared to the ground state. The barrier was found to be dependent on the position of benzannulation, since one derivative was found to switch as fast as the nonbenzannulated molecule although with lower efficiency, whereas another derivative completely lost the ability to undergo reversible photoswitching. The findings herein provide novel principles for the design of molecular photoswitches, shedding new light on excited state aromaticity, as previous discussions have mainly considered excited state aromaticity to be beneficial to switching. Our findings show that this view must be reconsidered.[a] Mr.