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Aryl‐maleimides undergo a novel [2+4]‐photodimerization instead of the expected [2+2]‐photodimerization under both direct irradiation with visible light and under sensitized energy transfer conditions. This new excited state reactivity in aryl‐maleimides is deciphered through photochemical, photophysical, and spectroscopic studies. The stereochemistry of the photodimer depends on the type of non‐bonding interactions prevalent during photodimerization which is in turn dictated by the substituents on the maleimide ring. More importantly, the stereochemistry of the photodimer formed is complementary to the product observed under thermal conditions. [ABSTRACT FROM AUTHOR]

The study evaluates compatibility of stabilizers with dye doped liquid crystal (LC) scaffolds that are used in electronically dimmable materials. The photodegradation of the materials was investigated and suitable stabilizers were evaluated to slow the degradation process. Various types of benzotriazole‐based stabilizers were evaluated for stabilizing the liquid crystals. Based on spin trapping experiments, radicals generated upon UV exposure is likely responsible for the degradation of the system. The radical generation is competitively inhibited by the addition of stabilizers. [ABSTRACT FROM AUTHOR]

The title compound, [Cu2(C19H23N7O)(C2H3O2)4]n, was obtained via reaction of copper(II) acetate with the coordinating ligand, 6-ethoxy-N²,N4-bis[2-(pyridin-2-yl)ethyl]-1,3,5-triazine-2,4-diamine. The crystallized product adopts the monoclinic P21/c space group. The metal core exhibits a paddle-wheel structure typical for dicopper tetraacetate units, with triazine and pyridyl nitrogen atoms from different ligands coordinating to the two axial positions of the paddle wheel in an asymmetric manner. This forms a coordination polymer with the segments of the polymer created by the c-glide of the P21/c setting of the space group. The resulting chains running along the c-axis direction are held together by intramolecular N--H…O hydrogen bonding. These chains are further packed by dispersion forces, producing an extended three-dimensional structure. [ABSTRACT FROM AUTHOR]

A series of covalently bound phenothiazine ( PHZ) donor and methylviologen (V) acceptor compounds with polymethylene chain spacers (C8, C10, C12) were incorporated in a 'through-ring' (rotaxane) fashion to α-cyclodextrin ( α- CD) hosts such that the alkyl chains were fully extended, with the donor and acceptor on opposite sides of the α- CD cylinder. Photoexcitation of the PHZ unit induces electron transfer from the PHZ first excited triplet state to the V moiety, forming a biradicaloid charge-separated state. Time-resolved electron paramagnetic resonance ( TREPR) spectroscopy at the X-band and Q-band microwave frequencies was used to investigate the spin exchange interaction, J, in these biradicaloids. Simulation of the spectra using a 'static' model for spin-correlated radical pairs allows extraction of the J values, which are negative in sign and have absolute values range from 2 to 1000 Gauss. Comparison of the PHZnV ( n = 8, 10, 12) spectra to those obtained using phenyl ether spacers indicates that π-bonds may assist the electronic coupling. The results are discussed in terms of through-bond vs through-space electronic coupling mechanisms. [ABSTRACT FROM AUTHOR]

Solvent and temperature dependent paramagnetism is reported for the complex [RuII(bpy)2(phendione)]- (PF6)2 (bpy = 2,2'-bipyridine, phendione = 1,10-phenanthroline-5,6-dione), 1. Magnetometry, ¹H-NMR, EPR and substituent effects confirm that the paramagnetic character is localized on the phendione ligand, and arises due to mixing of the MLCT excited state with an open shell triplet state on the phendione moiety, a process that is most likely driven by aromatization. The stabilized open shell phendione structure, in which the triplet lies lower in energy than the singlet, can then be thermally populated from the ground state of the complex. This process is facilitated by admixture of singlet character from the MLCT state. Paramagnetic behavior is absent in the free phendione ligand, and disappears in the presence of Lewis acids and in the presence of water due to hydrogen bonding (or hydrate formation at sufficient water concentrations). Control experiments rule out the presence of monoradicals such as semiquinone anions. Implications for spin filtering, sensing, and other electronic applications using such structures are discussed. [ABSTRACT FROM AUTHOR]

The study evaluates compatibility of stabilizers with dye doped liquid crystal (LC) scaffolds that are used in electronically dimmable materials. The photodegradation of the materials was investigated and suitable stabilizers were evaluated to slow the degradation process. Various types of benzotriazole‐based stabilizers were evaluated for stabilizing the liquid crystals. Based on spin trapping experiments, radicals generated upon UV exposure is likely responsible for the degradation of the system. The radical generation is competitively inhibited by the addition of stabilizers. [ABSTRACT FROM AUTHOR]

Solvent and temperature dependent paramagnetism is reported for the complex [RuII(bpy)2(phendione)]- (PF6)2 (bpy = 2,2'-bipyridine, phendione = 1,10-phenanthroline-5,6-dione), 1. Magnetometry, ¹H-NMR, EPR and substituent effects confirm that the paramagnetic character is localized on the phendione ligand, and arises due to mixing of the MLCT excited state with an open shell triplet state on the phendione moiety, a process that is most likely driven by aromatization. The stabilized open shell phendione structure, in which the triplet lies lower in energy than the singlet, can then be thermally populated from the ground state of the complex. This process is facilitated by admixture of singlet character from the MLCT state. Paramagnetic behavior is absent in the free phendione ligand, and disappears in the presence of Lewis acids and in the presence of water due to hydrogen bonding (or hydrate formation at sufficient water concentrations). Control experiments rule out the presence of monoradicals such as semiquinone anions. Implications for spin filtering, sensing, and other electronic applications using such structures are discussed. [ABSTRACT FROM AUTHOR]

Aryl-maleimides undergo a novel [2+4]-photodimerization instead of the expected [2+2]-photodimerization under both direct irradiation with visible light and under sensitized energy transfer conditions. This new excited state reactivity in aryl-maleimides is deciphered through photochemical, photophysical, and spectroscopic studies. The stereochemistry of the photodimer depends on the type of non-bonding interactions prevalent during photodimerization which is in turn dictated by the substituents on the maleimide ring. More importantly, the stereochemistry of the photodimer formed is complementary to the product observed under thermal conditions., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The title compound, [Cu 2 (C 19 H 23 N 7 O)(C 2 H 3 O 2 ) 4 ] n , was obtained via reaction of copper(II) acetate with the coordinating ligand, 6-eth-oxy- N 2 , N 4 -bis-[2-(pyridin-2-yl)eth-yl]-1,3,5-triazine-2,4-di-amine. The crystallized product adopts the monoclinic P 2 1 / c space group. The metal core exhibits a paddle-wheel structure typical for dicopper tetra-acetate units, with triazine and pyridyl nitro-gen atoms from different ligands coordinating to the two axial positions of the paddle wheel in an asymmetric manner. This forms a coordination polymer with the segments of the polymer created by the c -glide of the P 2 1 / c setting of the space group. The resulting chains running along the c -axis direction are held together by intra-molecular N-H⋯O hydrogen bonding. These chains are further packed by dispersion forces, producing an extended three-dimensional structure., (© Ayodele et al. 2021.)

UV-irradiation of a self-assembled benzophenone bis-urea macrocycle generates μm amounts of radicals that persist for weeks under ambient conditions. High-field EPR and variable-temperature X-band EPR studies suggest a resonance stabilized radical pair through H-abstraction. These endogenous radicals were applied as a polarizing agent for magic angle spinning (MAS) dynamic nuclear polarization (DNP) NMR enhancement. The field-stepped DNP enhancement profile exhibits a sharp peak with a maximum enhancement of ϵ on/off =4 superimposed on a nearly constant DNP enhancement of ϵ on/off =2 over a broad field range. This maximum coincides with the high field EPR absorption spectrum, consistent with an Overhauser effect mechanism. DNP enhancement was observed for both the host and guests, suggesting that even low levels of endogenous radicals can facilitate the study of host-guest relationships in the solid-state., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Solvent and temperature dependent paramagnetism is reported for the complex [Ru(II)(bpy)2(phendione)](PF6)2 (bpy = 2,2'-bipyridine, phendione = 1,10-phenanthroline-5,6-dione), . Magnetometry, (1)H-NMR, EPR and substituent effects confirm that the paramagnetic character is localized on the phendione ligand, and arises due to mixing of the MLCT excited state with an open shell triplet state on the phendione moiety, a process that is most likely driven by aromatization. The stabilized open shell phendione structure, in which the triplet lies lower in energy than the singlet, can then be thermally populated from the ground state of the complex. This process is facilitated by admixture of singlet character from the MLCT state. Paramagnetic behavior is absent in the free phendione ligand, and disappears in the presence of Lewis acids and in the presence of water due to hydrogen bonding (or hydrate formation at sufficient water concentrations). Control experiments rule out the presence of monoradicals such as semiquinone anions. Implications for spin filtering, sensing, and other electronic applications using such structures are discussed.