Synthesis of Photochromic Phosphines by Pd-Catalyzed Annulation Reaction of Alkynes Bearing Phosphinyl Substituent with a Silacyclopropene

The synthesis of phosphines with light controlled basicity is presented in this study. A methodological approach for the preparation of these unconventional photochromic phosphines based on a dithienylethene organic moiety is reported. It relies on the palladium-catalyzed annulation of alkynyl phosphines in the presence of a 2,3-Dithienylsilacyclopropene. Accordingly, a diphenyphosphino moiety is connected to the organic photochrome thanks to different linkers. Their influence on the photochromism and on the phosphinyl group basicity is studied and evaluated based on experimental an NMR descriptor as well as DFT calculations.

Synthesis and Properties of Spiro-double Sila[7]helicene: The LUMO Spiro-conjugation

A double helicene with a spiro-Si linker (4) was synthesized by four successive nucleophilic substitutions on SiCl₄ . Its (P,P), (M,M) and (P,M) isomers were isolated and characterized by single crystal X-ray analysis. Due to the central spirosilabi[fluorene] moiety, the two helicene units in 4 are symmetrically and nearly perpendicularly arranged. (P,P)-4 and (M,M)-4 exhibit unique optical properties attributable to the LUMO spiro-conjugation between the two sila[7]helicene units.

Chiral Benzo[b]silole-Fused 9,9'-Spirobi[fluorene]: Synthesis, Chiroptical Properties, and Transformation to π-Extended Polycyclic Arene

Chiral spiro π-conjugated compounds have emerged as a new class of circularly polarized luminescent organic materials. Here we report the synthesis and (chir)optical properties of a chiral benzo[b]silole-fused 9,9'-spirobi[fluorene] (SBF) and π-extended spiro polycyclic arene. The benzo[b]silole-fused SBF was successfully synthesized by a rhodium-catalyzed intramolecular silylative cyclization. It was further transformed to the chiral π-extended spiro polycyclic arene by an annulative π-extension reaction. Less effective spiroconjugation was observed for these spiro compounds through UV-Vis absorption spectroscopy and theoretical calculations. They exhibit circularly polarized luminescence with the dissymmetry factors of up to 0.76×10^-3 . Theoretical calculations demonstrate that emission of the benzo[b]silole-fused SBF occurs from one subunit, the structure of which is slightly different from that in the Frank-Condon state.

The Combination of Cross-Hyperconjugation and σ-Conjugation in 2,5-Oligosilanyl Substituted Siloles

Reaction of a 2,5-dilithiated silole with excess dichlorodimethylsilane gives the respective 2,5-bis(chlorodimethylsilyl) substituted silole. This compound can be converted to 2,5-bis(oligosilanyl) substituted siloles by addition of a suitable oligosilanide. In the UV spectra of the thus obtained compounds the lowest energy absorptions are bathochromically shifted compared to the absorptions of the two constituents, namely the 2,5-disilyl substituted silole and a trisilane. The bathochromic shift is interpreted as being caused by a mixed σ-conjugation/cross-hyperconjugation. This assumption is supported by TD-DFT calculations, which show a significant contribution from Si-Si bonds to the HOMO of the molecule.

Benzosiloles with Crystallization-Induced Emission Enhancement of Electrochemiluminescence: Synthesis, Electrochemistry, and Crystallography

Crystallization-induced emission enhancement (CIEE) was demonstrated for the first time for electrochemilunimescence (ECL) with two new benzosiloles. Compared with their solution, the films of the two benzosiloles gave CIEE of 24 and 16 times. The mechanism of the CIEE-ECL was examined by spooling ECL spectroscopy, X-ray crystal structure analysis, photoluminescence, and DFT calculations. This CIEE-ECL system is a complement to the well-established aggregation-induced emission enhancement (AIEE) systems. Unique intermolecular interactions are noted in the crystalline chromophore. The first heterogeneous ECL system is established for organic compounds with highly hydrophobic properties.

Helicenes Built from Silacyclopentadienes via Ring-by-Ring Knitting of the Helical Framework

Despite the apparent diversity of the protocols developed for the synthesis of helicenes, they essentially follow the same strategy: the closure of one, or several, internal rings in a key step. Herein, we report the synthesis of a new family of the heterohelicenes consisting of fused silacyclopentadiene rings formed via a facile and novel process. The treatment of oligo(alkynilydenesilylene) precursors of type H₂ C=CH-(SiMe₂ -C≡C)_n -R (n=3-7), bearing a vinyl group on the terminal silicon atom, with 9-borabicyclononane leads first to 1,2-hydroboration of the terminal double bond which then continues with a cascade of intramolecular 1,1-carboboration reactions accompanied with the closure of a new silole ring after each step affording the target silahelicenes with, currently, up to seven condensed silole rings and with excellent yields. According XRD analysis, the seven fused silole rings of the heptacyclic compound 11 b form an almost complete turn of a helix. The presented one-pot sequence of reactions is the first example of ring-by-ring knitting of a helical framework starting from easily available linear precursors.

Influences of Conjugation Extent on the Aggregation-Induced Emission Quantum Efficiency in Silole Derivatives: A Computational Study

The photophysical properties of a series of silole derivatives, with hydrogen (TPS), bromine (BrTPS), and conjugated phenyl (HPS), triphenylsilyethynyl (BTPES), and dimethylfluorene (BFTPS) substituents at 2,5-positions in both gas and aggregate phases have been investigated computationally by employing the correlation function rate formalism coupled with a hybrid quantum/molecular mechanics (QM/MM) approach. It is found that the solid-state fluorescence quantum efficiency first increases sharply with the degree of π-conjugation of the 2,5-substituents, then levels off, and finally starts to decrease slightly. This is because the side-group conjugation tends to enhance the radiative decay rate in both gas and solid phases. However, a further increase in conjugation leads to saturation in the radiative decay rate but increases the non-raditiave decay rate due to the decreased energy gap.

Synthesis, structure, photoluminescence, and electroluminescence of siloles that contain planar fluorescent chromophores

Herein, a new series of siloles that were 2,5-substituted with planar fluorescent chromophores (PFCs), including fluorene, fluoranthene, naphthalene, pyrene, and anthracene, were synthesized and characterized. These compounds showed weak emission in the solution state, owing to active intramolecular rotation (IMR), but the synergistic effect from electronic coupling between the PFC and the silole ring compensated for the emission quenching by the IMR process to some extent, thereby affording higher emission efficiencies than those of 2,3,4,5-tetraphenylsiloles in solution. These new siloles showed enhanced emission efficiencies in the aggregated state. The electroluminescence (EL) color and efficiency of new siloles were sensitive towards the PFC. Siloles containing naphthalene moieties showed green EL emission, whilst those containing anthracene moieties showed orange EL emission. The siloles containing pyrene moieties exhibited yellow EL emission at 546 nm, with a peak luminance of 49000 cd cm(-2) and a high current efficiency of 9.1 cd A(-1).

2,5-difluorenyl-substituted siloles for the fabrication of high-performance yellow organic light-emitting diodes

2,3,4,5-Tetraarylsiloles are a class of important luminogenic materials with efficient solid-state emission and excellent electron-transport capacity. However, those exhibiting outstanding electroluminescence properties are still rare. In this work, bulky 9,9-dimethylfluorenyl, 9,9-diphenylfluorenyl, and 9,9'-spirobifluorenyl substituents were introduced into the 2,5-positions of silole rings. The resulting 2,5-difluorenyl-substituted siloles are thermally stable and have low-lying LUMO energy levels. Crystallographic analysis revealed that intramolecular π-π interactions are prone to form between 9,9'-spirobifluorene units and phenyl rings at the 3,4-positions of the silole ring. In the solution state, these new siloles show weak blue and green emission bands, arising from the fluorenyl groups and silole rings with a certain extension of π conjugation, respectively. With increasing substituent volume, intramolecular rotation is decreased, and thus the emissions of the present siloles gradually improved and they showed higher fluorescence quantum yields (Φ(F) =2.5-5.4%) than 2,3,4,5-tetraphenylsiloles. They are highly emissive in solid films, with dominant green to yellow emissions and good solid-state Φ(F) values (75-88%). Efficient organic light-emitting diodes were fabricated by adopting them as host emitters and gave high luminance, current efficiency, and power efficiency of up to 44,100 cd m(-2), 18.3 cd A(-1), and 15.7 lm W(-1), respectively. Notably, a maximum external quantum efficiency of 5.5% was achieved in an optimized device.