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.