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Due to its high electron affinity and electron mobility in a wide absorption range of the visible solar spectrum, [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) is often used as an efficient acceptor in organic photovoltaics. In turn, imines are additives to the active layer of organic solar cells, mainly due to the free electron pair of the imine nitrogen atom and the presence of various chemical groups affecting the polarity and conformations of molecules. However, the attainable efficiency is not as high as expected. Therefore, we have systematically investigated two imines and their mixtures with PC71BM by spectroscopic (the high pressure UV–Vis and frequency domain dielectric), thermoelectric, and mechanical methods for organic, flexible photovoltaics. Both the imines, (N,NʹE,N,NʹE)-N,Nʹ-([2,2ʹ:5ʹ,2ʺ-terthiophene]-5,5ʺ-diylbis(methanylylidene))bis(benzo[d]thiazol-2-imine) (SC3) and (6E)-N-((5-(5-(5-((E)-(4-(4-(4-fluorophenyl)thiazol-2-yl)phenylimino)methyl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)methylene)-4-(4-(4-fluorophenyl)thiazol-2-yl)benzenamine (SC13), have the same core composed of three thiophene rings but different terminal chains of the molecules. In the imine SC3, the imine bond is followed by benzothiazole rings on both sides of the core, while in SC13, a thiazole ring separates two benzene rings, the terminal one F-substituted. The difference in molecular structure affects the electric properties of the neat imine and its mixed layers. An addition of PC71BM to the imines improves their electric conductivity. The mechanical studies focused on the stress at break and elongation showed superior behaviour compared to fullerene derivative. High pressure systematically reduces the band gap energy, Eg, from 1.68 eV at 0.16 GPa to 1.51 eV at 2.69 GPa for PC71BM, from 1.77 eV at 0.1 MPa to 1.53 eV at 4.15 GPa for SC3, and from 1.99 eV at 0.11 GPa to 1.8 eV at 3.10 GPa for SC13, as determined by the UV–Vis absorbance measurements in a diamond-anvil cell. These Eg reductions reflect the compressed intermolecular interactions that can be used to monitor the structural stability of these compounds. Based on the dielectric studies it was found that the relaxation processes registered for both imines are probably the grain boundary relaxation. Two processes also appear in the systems with PC71BM, but none of them is the one characteristic of imines. The high-frequency process has a dipole character while the low-frequency one is probably the grain boundary relaxation of these systems. The mechanism of quasi-DC conduction in various temperature ranges in the studied systems was also determined. [ABSTRACT FROM AUTHOR]

Phenyl-substituted perylene diimide (PTCDI-Ph) derivatives are prospective organic, electronic and optoelectronic materials. In this study, the effects of modified intermolecular interactions and molecular conformations on the energy gap and the optical properties of PTCDI-Ph were explored at high pressure and various temperatures by calorimetry, X-ray diffraction, UV-vis absorption, and photoluminescence spectroscopy. Below 498 K, PTCDI-Ph transforms from phase I to phase II, which is stable down to 93 K at least. Above 3.0 GPa, phase II transforms into phase III. The compressed intermolecular distance between perylene cores linearly narrows the band gap, due to the intensified π–π stacking. The negative linear compressibility of the crystal along [100] coincides with the negative thermal expansion in this direction. Owing to the strong pressure and temperature dependence of the luminescence spectrum, the PTCDI-Ph derivatives constitute a promising class of highly stimuli-responsive elastic organic materials with broad potential for tailoring their optoelectronic properties through physical and chemical modifications. [ABSTRACT FROM AUTHOR]

Inherent features of metal halide perovskites are their softness, complex lattice dynamics, and phase transitions spectacularly tuning their structures and properties. While the structural transformations are well described and classified in 3D perovskites, their 1D analogs are much less understood. Herein, both temperature- and pressure-dependent structural evolutions of a 1D AcaPbI 3 perovskitoid incorporating acetamidinium (Aca) cation are examined. The study reveals the existence of nine phases of δ-AcaPbI 3 , which present the most diverse polymorphic collection among known perovskite materials. Interestingly, temperature- and pressure-triggered phase transitions in the 1D perovskotoid exhibit fundamentally different natures: the thermal transformations are mainly associated with the collective translations of rigid polyanionic units and ordering/disordering dynamics of Aca cations, while the compression primarily affects inorganic polymer chains. Moreover, in the 1-D chains featuring the face-sharing connection mode of the PbI 6 octahedra the Pb···Pb distances are significantly shortened compared to the corner-sharing 3D perovskite frameworks, hence operating in the van der Waals territory. Strikingly, a good correlation is found between the Pb···Pb distances and the pressure evolution of the bandgap values in the δ-AcaPbI 3 , indicating that in 1D perovskitoid structures, the contacts between Pb 2+ ions are one of the critical parameters determining their properties., (© 2024 Wiley‐VCH GmbH.)

Invited for the cover of this issue is the group of Andrzej Katrusiak at Adam Mickiewicz University. The image depicts a wave and the sun, which represent the high energy required for the high-entropy nucleation reported in this work. Read the full text of the article at 10.1002/chem.202005121., (© 2021 Wiley-VCH GmbH.)