Absorption spectra of cyanine ⊕ •Br ⊖ salts show a remarkable solvent dependence in non/polar solvents, exhibiting narrow, sharp band shapes in dichloromethane but broad features in toluene; this change was attributed to ion pair association, stabilizing an asymmetric dipolar structure, similar to the situation in the crystal (Bouit, P.-A., et al. J. Am. Chem. Soc. 2010, 132, 4328). Our density functional theory (DFT)-based quantum mechanics/molecular mechanics (QM/MM) calculations of the crystals evidence the crucial role of specific asymmetric anion positioning on the lowering of the symmetry. Molecular dynamics (MD) simulations prove the ion pair association in nonpolar solvents. Time-dependent DFT vibronic calculations in toluene show that ion pairing indeed stabilizes an asymmetric dipolar structure in the electronic ground state. This largely broadens the absorption spectrum in very reasonable agreement with experiment, while the principal pattern of vibrational modes is retained. The current findings allow us to establish a unified picture of the symmetry breaking of polymethine dyes in fluid solution.

Cyanoarene-based photocatalysts (PCs) have attracted significant interest owing to their superior catalytic performance for radical anion mediated photoredox catalysis. However, the factors affecting the formation and degradation of cyanoarene-based PC radical anion (PC•‒) are still insufficiently understood. Herein, we therefore investigate the formation and degradation of cyanoarene-based PC•‒ under widely-used photoredox-mediated reaction conditions. By screening various cyanoarene-based PCs, we elucidate strategies to efficiently generate PC•‒ with adequate excited-state reduction potentials (Ered*) via supra-efficient generation of long-lived triplet excited states (T1). To thoroughly investigate the behavior of PC•‒ in actual photoredox-mediated reactions, a reductive dehalogenation is carried out as a model reaction and identified the dominant photodegradation pathways of the PC•‒. Dehalogenation and photodegradation of PC•‒ are coexistent depending on the rate of electron transfer (ET) to the substrate and the photodegradation strongly depends on the electronic and steric properties of the PCs. Based on the understanding of both the formation and photodegradation of PC•‒, we demonstrate that the efficient generation of highly reducing PC•‒ allows for the highly efficient photoredox catalyzed dehalogenation of aryl/alkyl halides at a PC loading as low as 0.001 mol% with a high oxygen tolerance. The present work provides new insights into the reactions of cyanoarene-based PC•‒ in photoredox-mediated reactions.

Research on solvent-free acrylic pressure-sensitive adhesives (PSAs) has tremendously grown over the last few decades due to the stringent regulations to control volatile organic compound emissions. They are mostly prepared...

Polymorphs of organic semiconductors are of great interest as they shed light to structure-property relationships. The full X-ray thin film structure analysis of two polymorphs (B, G) of an important n-type semiconducting dicyanodistyrylbenzene based small molecule (CN-TFPA) is reported. Drastically different structures of the monotropic phases are revealed, that is an uncommon 2D crossed π-stacked arrangement for the B-phase versus a 1D slipped π-stack for G. Both phases exhibit a layered structure in the (100) plane with high structural integrity, driven by the hydrophobic contacts of the terminal CF 3 groups; as (100) coincides with the film surface, this allows for exfoliation by scotch tape. An in-depth time-dependent density functional theory (TD-DFT) based quantum mechanics/molecular mechanics (QM/MM) study reveals all subsequent significantly differing optical and electronic responses which result from the different arrangements: the B film shows little excitonic interaction with strong blue fluorescence, amplified spontaneous emission (ASE), and good 2D n-type transport. The G film forms H-aggregates with strong green fluorescence, no ASE, and 1D n-type charge transport. The established structure-property relationships are seen as a crucial step for computer-aided device analysis. Luminescent PolymorphsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Boric acid (BA) has been used as a transparent glass matrix for optical materials for over 100 years. However, recently, apparent room‐temperature phosphorescence (RTP) from BA (crystalline and powder states) was reported (Zheng et al., Angew. Chem. Int. Ed. 2021, 60, 9500) when irradiated at 280 nm under ambient conditions. We suspected that RTP from their BA sample was induced by an unidentified impurity. Our experimental results show that pure BA synthesized from B(OMe)3 does not luminesce in the solid state when irradiated at 250–400 nm, while commercial BA indeed (faintly) luminesces. Our theoretical calculations show that neither individual BA molecules nor aggregates would absorb light at >175 nm, and we observe no absorption of solid pure BA experimentally at >200 nm. Therefore, it is not possible for pure BA to be excited at >250 nm even in the solid state. Thus, pure BA does not display RTP, whereas trace impurities can induce RTP.

The performance of different DFT functionals (B3LYP, BHLYP, CAM-B3LYP, M06HF) on the prediction of vertical transition energies E vert of low bandgap homopolymers is tested against the experimentally available oligomer series (thienopyrazines and thienothiophenes). This allows for a detailed and accurate comparison on the consistency of DFT methods for chainlength evolution and polymer limit prediction, and for an understanding of geometry and time-dependent contributions to E vert by combinatorial analysis. Together with former studies on wide/medium bandgap polymers and low bandgap co-polymers, our results on low bandgap homopolymers suggest offset-corrected M06HF as the most viable method for time inexpensive and reliable prediction of semiconducting polymers at the moment.

Among the new materials currently employed as electron donor element in active layers of organic solar cells (OSCs), PTB7 holds the best results. It has been extensively studied and now there is a search for new derivatives to improve its properties. In this work, a set of 24 polymers derived from polythieno[3,4b]-thiophene-co-benzodithiophene (PTB7) was studied theoretically, using chemical modifications in the benzodithiophene (BDT) moiety of the PTB7 monomeric units. After evaluations of the electronic and optical properties, including the open circuit voltage and exciton dissociation and recombination conditions, the results indicate that employing chlorine as substituent yields the most promising material for application in active layers together with Phenyl-C 61-Butyric-Acid-Methyl-Ester (PCBM) as electron acceptor material.

Nowadays, the development of new materials for applications in flexible optoelectronic devices is one of the main frontiers of science. However, in order to improve the applicability and durability of such devices, a deeper understanding of the effects induced by mechanical deformations on the properties of their components is still necessary. In this sense, in the present study, it is evaluated the effect of mechanical stretching in the structural, electronic, and optical responses of two widely investigated organic polymers with great technological interest: poly(2-methoxy,5-(2 0ethylhexyloxy)-1,4-phenylene vinylene) and poly(3-hexylthiophene-2,5-diyl). Hartree-Fock and density functional theory electronic structure calculation methods were employed for the study of oligomeric structures subjected to increasing stretch levels along the polymerization axis. The results show a dependence of the polymer properties with the mechanical deformation, allowing to identify distinct response regimes according to the main chain stretching. In particular, it is noticed that large stretches lead to nonfunctional devices, mainly due to the localization of the frontier orbitals and degradation of optoelectronic properties. In addition, it was also identified that very small deformations can lead to some interesting optoelectronic responses, which could indicate an alternative route for the design of organic devices via mechanical processes.