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A series of σ-π extended octamethyltetrasilanes, which have phenothiazine, 9,9-dimethyl-9,10-dihydroacridine, or phenoxazine ( 1 , 2 , and 3 ) groups as donor moieties and thienopyrazine or benzothiadiazole ( a and b ) groups as acceptor fragments, has been prepared, and their optical properties have been studied as an extension of our work. All six compounds exhibited fluorescence in the solid state with maximum wavelengths centered in the range of 400 and 650 nm upon excitation by a UV lamp. Compound 2b showed apparent dual emission behavior in solution, which depends on solvent polarity, and a reversible photoluminescent change under mechanical and thermal stimuli in the solid state. Quantum chemical calculations suggest the contribution of a quasi-axial conformer of the 9,9-dimethyl-9,10-dihydroacridine moiety in 2b to the dual emission in solution and the mechanofluoroluminescence in the solid state, similarly to 1a . These studies provide new insight into the preparation of disilane-bridged triads capable of responding to multiple stimuli.

A series of disilane-linked donor‒acceptor‒donor triads (D‒Si‒Si‒A‒Si‒Si‒D) was synthesized to investigate the effects of substituents on the photophysical properties. The triads were prepared by metal-catalyzed diiodosilylation of aryl iodides using a Pd(P( t -Bu)₃)₂/( i -Pr)₂EtN/toluene system that we previously developed. Optical measurements, X-ray diffraction analysis, and density functional theory calculations revealed relationships between the photophysical properties and molecular structures of these triads in solution and in the solid state. The compounds emitted blue to green fluorescence in CH₂Cl₂ solution and in the solid state. Notably, compound 2 showed fluorescence with an absolute quantum yield of 0.17 in the solid state but showed no fluorescence in CH₂Cl₂. Our findings confirmed that the substituent adjacent to the disilane moiety affects the conformations and emission efficiencies of compounds in solution and in the solid state.

Controlling the coordination environments and the luminescence properties of Eu(3+) complexes with outer-sphere counterions was achieved in the solid state, in a polymer matrix and in solution.

The luminescence of stable radicals can be enhanced by coordination to metal complexes. The 4% fluorescence quantum yield of (3,5-difluoro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (F2PyBTM) in dichloromethane was enhanced up to 36% by coordination to AuI with N-heterocyclic carbene ligand, which is a record for metal-radical complexes. [ABSTRACT FROM AUTHOR]

A σ–π extended aryldisilane, comprising a thienopyrazine group as an acceptor fragment and phenothiazine groups as the donor moiety, has been prepared through the introduction of two Si−Si bridges (compound 1). X‐ray diffraction analysis determined the crystal structure of 1, and experimental and theoretical approaches investigated its optical properties. Solvatochromic studies revealed the dual emission of 1 in all solvents tested. Compound 1 also exhibited fluorescence in the solid state upon excitation with a hand‐held UV lamp, as well as mechanochromic luminescent properties. The packing mode in the crystal structure, variation of phenothiazine conformation, morphological changes between crystalline and amorphous phases are the major factors showing reversible fluorescence under external stimuli. A theoretical conformer study found that 1 exists in distinct conformational groups differing in Gibbs free energy by less than 3 kcal mol−1. The conformer in the crystalline state of 1 can promote the complete separation of the HOMO and LUMO between the phenothiazine donor and the thienopyrazine acceptor, linked by the disilane linker. HOMO–LUMO energy transition in the crystalline state is forbidden due to the lack of frontier orbital overlap. Crystalline state emission showed LUMO → HOMO−1 transition (locally excited (LE) state). In the amorphous state, the partial presence of quasi‐axial conformers allows intramolecular charge‐transfer type emission via energy transfer from dominant quasi‐equatorial conformers. The strategy proposed in this work provides important guidance for developing stimuli‐responsive materials with controlled excited states. [ABSTRACT FROM AUTHOR]

The excited‐state dynamics of the photostable luminescent organic radical (3,5‐dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl (PyBTM) doped in a host crystal was investigated by using optically detected magnetic resonance (ODMR) and time‐resolved emission spectroscopies. In the radical system, the unpaired electron can be used as the probe for studying the electronic state and its dynamics. The mixed crystal with a high concentration of the radical showed excimer emission, together with the monomer emission. The ODMR signals were observed with opposite signs for monitoring the monomer and the excimer emissions. Based on their temperature and concentration dependencies, the excited‐state dynamics on the doped crystal and the mechanism of the excimer formation and the ODMR signal generation are discussed with the help of the quantum mechanical simulation of the excited‐state spin dynamics. The initial process of excimer formation has been clarified for the first time from the viewpoint of the spin‐dynamics. The excited‐state dynamics of a photostable luminescent organic radical doped in a host crystal was investigated by using optically detected magnetic resonance (ODMR) and time‐resolved emission spectroscopies. The initial process in excimer formation was clarified for the first time from the viewpoint of the spin dynamics. [ABSTRACT FROM AUTHOR]

The organotin precursors 6‐Br‐Ace‐5‐SnBu3 (6, Ace = acenaphthyl) and 6‐Ph2E‐Ace‐5‐SnBu3 (7a: E = P; 7b: E = As; 7c: E = Sb) were prepared and used for the synthesis of organogold complexes, namely, the homodinuclear arylgold(I) species (6‐Ph2E‐Ace‐5‐Au)2 (8a: E = P; 8b: E = As; 8c: E = Sb), arylgold(III) dichloride 6‐Ph2P‐Ace‐5‐AuCl2 (9), diarylgold(III) chloride [trans‐(6‐Ph2P‐Ace‐5‐)2Au]Cl ([10]Cl), as well as the heterodinuclear gold complexes 6‐Ph2P(AuX)‐Ace‐5‐Au(AsPh3) (11a: X = Cl; 11b: X = Br). Compounds 8a ‐ 8c, 11a, and 11b show significant aurophilic interactions, which are related to their photoluminescence upon exposure to UV light. In the solid state, 11a and 11b show green‐yellow emission, whereas 8a ‐ 8c are non‐emissive. In solution under an argon atmosphere, all five compounds 8a ‐ 8c as well as 11a and 11b show green‐yellow emission. The organogold complexes were characterized by multinuclear NMR spectroscopy, photoluminescence spectroscopy, single‐crystal X‐ray crystallography, as well as (TD‐)DFT calculations including real‐space bond indicators derived from atoms‐in‐molecules (AIM), the electron localization indicator (ELI‐D), and the non‐covalent interaction (NCI) index. Switch on the light: The reaction of the homodinuclear (6‐diphenylpnicogenoacenaphth‐5‐yl)gold(I) species (6‐Ph2P‐Ace‐5‐Au)2 (left) with Ph3AsAuCl gives rise to the formation of the heterodinuclear gold(I) complex 6‐Ph2P(AuCl)‐Ace‐5‐Au(AsPh3) (right), which shows green‐yellow photoluminescence. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the emission properties of a photostable luminescent organic radical, (3,5‐dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl radical (PyBTM), doped into host molecular crystals. The 0.05 wt %‐doped crystals displayed luminescence attributed to a PyBTM monomer with a room‐temperature emission quantum yield of 89 %, which is exceptionally high among organic radicals. The 10 wt %‐doped crystals exhibited both PyBTM monomer and excimer‐centered emission bands, and the intensity ratio of these two bands was modulated drastically by applying a magnetic field of up to 18 T at 4.2 K. This is the first observation of a magnetic field affecting the luminescence of organic radicals, and we also proposed a mechanism for this effect. [ABSTRACT FROM AUTHOR]

The open-shell luminescent (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl (PyBTM) radical contains a nitrogen atom that behaves as a stimulus-responsive site. Chemical modification at this nitrogen atom, such as coordination of B(C6F5)3 or methylation, shifts the emission maximum to the low-energy region and increases the reduction potential. The emission colour may be regulated by the reversible Lewis acid-base reaction between B(C6F5)3 and PyBTM. Comparison of the optical and electrochemical properties of the radicals with the electronic structures calculated by density functional theory has indicated that the chemical modification decreased the energy level of the β-singly occupied molecular orbital, a key orbital in determining the optical and electrochemical properties of such systems. [ABSTRACT FROM AUTHOR]

A rational molecular design for open-shell molecules to enhance their luminescence efficiency was developed. Introduction of fluorine atoms and coordination of gold(i) to PyBTM, a highly stable fluorescent radical containing a pyridyl moiety, synergistically contributed to yield ten times increase of its fluorescence quantum yield (2 → 20%). [ABSTRACT FROM AUTHOR]

A gold(I) complex containing an open-shell luminescent (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl (PyBTM) radical was prepared. The complex showed fluorescence centered mainly on the coordinated PyBTM ligand. The photophysical and photochemical properties were positively modulated upon coordination to AuI; the photoluminescence quantum yield, fluorescence wavelength, and the stability in the photoexcited state all increased. [ABSTRACT FROM AUTHOR]

A luminescent open-shell organic radical with high chemical stability was synthesized. (3,5-Dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) was photoluminescent under various conditions. Fluorescence quantum yields of 0.03, 0.26, and 0.81 (the highest value reported for a stable organic radical) were obtained in chloroform, in poly(methyl methacrylate) film at room temperature, and in an EPA matrix (diethyl ether:isopentane:ethanol) at 77 K, respectively. The photostability of PyBTM is up to 115 times higher than that of the tris(2,4,6-trichlorophenyl)methyl radical, a previously reported luminescent radical. The pyridine moiety of PyBTM acts as a proton coordination site, thereby allowing for control of the electronic and optical properties of the radical by protonation and deprotonation. [ABSTRACT FROM AUTHOR]

Water-soluble luminescent AuNPs of 1.3 ± 0.3 nm in diameter with a large Stokes shift were facilely synthesized by a new molten matrix sputtering (MMS) method. [ABSTRACT FROM AUTHOR]

Excimers. The excited‐state dynamics of a photostable luminescent organic radical was reported by Y. Teki and co‐workers in their Communication on page 2606 ff. The initial process in excimer formation was clarified for the first time from the viewpoint of the spin‐dynamics. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Planar chiral organosilanes were prepared from dioxacyclophane as a building block. • Absolute configurations were determined by single-crystal X-ray analysis. • (+)-(R)- 2 exhibited circularly polarized luminescence for a small organic molecule. Abstract Planar chiral dioxacyclophanes were designed and synthesized as a key scaffold for materials with circularly polarized luminescence (CPL). Representative planar chiral 1,12-dioxa[12](1,4)naphthaleneophane-derived organosilane compounds (−)-(R)- 1 , (+)-(R)- 2 , and (−)-(R)- 3 were prepared by (+)-sparteine-mediated aryl metalation and an electrophilic reaction with chlorosilanes. The absolute configurations of the planar chirality were determined in the R form by single-crystal X-ray analysis. Optically active compound (+)-(R)- 2 exhibited blue fluorescence and a CPL signal with a dissymmetry factor (g lum value) of 0.001 in solution. The electronic structure was corroborated by DFT and TD-DFT calculations rationalizing the observed spectroscopic properties. [ABSTRACT FROM AUTHOR]

Acid-induced double lactonization in triarylamine-conjugated dimethyl diethynylfumarate E-1 opens up a new synthetic route to Pechmann dyes. This one-pot reaction affords three donor-acceptor-donor quadrupolar molecules (P55-1, P66-1, and P56-1); P56-1 comprises a missing structural isomer of Pechmann dyes. They are intensely colored and brightly luminescent. An organic field-effect transistor device fabricated with P66-1 functions as a p-type semiconductor. [ABSTRACT FROM AUTHOR]

We developed a new convertible copper(I) complex using 2-pyridyl-4-methylpyrimidine and diphosphine as ligands. This complex exhibited mechanical bistability based on the inversion motion of the pyrimidine ring, leading to dual luminescence behavior. The inversion dynamics was strongly dependent on temperature and solvent. Variable-temperature ¹H NMR spectra revealed that the two isomers interconverted in solution via ring inversion, and the motion was frozen below 200 K. The complex exhibited characteristic CT absorption and emission bands in solution. Emission lifetime measurements demonstrated that the emission could be deconvoluted into two components. The fast and slow components were assigned to the two isomers, the excited states of which were characterized by different structural relaxation process and/or additional solvent coordination properties. The emission properties of the two isomers differed not only in lifetime and wavelength but also in heat sensitivity. The molar ratio of the two isomers varied with the polarity of the solvent via electrostatic interactions with the counteranion. The rate of inversion was affected by solvent, suggesting that inversion was promoted by solvent coordination. [ABSTRACT FROM AUTHOR]

Pd-catalyzed coupling of 1,2-bis(silyl)arenes with 1,2-diiodoarenes provides access to various silicon-containing six-membered ring compounds. [ABSTRACT FROM AUTHOR]