Effects of Substitution on Solid-State Fluorescence in 9-Aryl-9-methyl-9H-9-silafluorenes

Hydrosilane/Organoiodine Coupling-Enabled Studies of Organosilane Physical Properties

ConspectusThis Account summarizes recent developments in metal-mediated coupling reactions between hydrosilanes and aryl iodides in the presence of Pd(P(t-Bu)3)2 and base. Alkylated organosilanes are obtained when Pt(P(t-Bu)3)2 and a base are employed in reactions between hydrosilanes and aliphatic iodides. These transformations show unusual reactivity compared to the typical behavior of hydrosilanes toward organoiodides in the presence of PdCl2 or PtCl2, and they proceed in high yields under mild conditions. In addition, the reaction demonstrates (1) high functional group tolerances, (2) stepwise introduction of substituents onto silicon atoms from secondary silanes, and (3) transformation without cleavage of weak Si-Si σ bonds in the molecules.This transformation can serve as a powerful tool for the synthesis of functional organosilicon compounds. The advantage is the flexibility in the molecular structure due to the large size compared to carbon. These compounds have relatively sparse packing in the crystalline state, unlike π-conjugated molecules, which induce dense π-π interactions. Consequently, they have significantly different physical properties in solution and in the solid state. Among them, aromatic disilanes and oligosilanes are important substance groups, because the conjugated chain within these molecules expands due to σ-π interaction between Si-Si σ bond and π orbital of aromatic ring. σ-π Conjugation is most efficient when the dihedral angle between the aromatic ring and the Si-Si bond is 90°, resulting in the overlap of σ orbital and π orbital. The conformational structure, packing, and physical properties of these compounds can change in tandem in response to external stimuli through a crystal phase transition. The interlocking changes in structure and physical properties are reversible, easily returning to their original state with different external stimulus. This account covers several important aspects, including solid-state emission with high fluorescence intensity, aggregation-induced emission (AIE) in water-THF system, mechanochromic fluorescence, organic light emitting diode (OLED), second harmonic generation (SHG) and thermosalient phenomena.This reaction can synthesize optically active tertiary and quaternary silanes by the enantioselective arylation of secondary silanes with aryl iodides using a palladium catalyst modified with a TADDOL-derived amide phosphoric acid ester as a chiral ligand. These optically active compounds can be used as useful circularly polarized luminescence (CPL) materials due to their strong luminescence intensity (Φ) and luminescence dissymmetry factor (glum) attributed to the chiral silicon atom. The efficient synthesis of sila-pharmaceuticals using this method as a key step is also described.The technique enables the design and synthesis of various silicon-containing bioactive substances and medical chemicals. Through the synthesis of organosilane compounds using this method, it is anticipated that the development of functional organic silanes will accelerate their practical applications in a wide range of fields.

Insights into the Aggregation Behaviour of a Benzoselenadiazole-Based Compound and Generation of White Light Emission

We have designed and synthesized the benzoselenadiazole (BDS) based donor-acceptor-donor (D-A-D) π-conjugated compound 4,7-di((E)styryl)benzo[2,1,3]selenadiazole (1). A single-crystal study of 1 shows J-type molecular aggregation in the solid state. The crystal packing of 1 shows head-to-head dimeric intermolecular assembly via Se⋅⋅⋅N interactions while staircase-type interlock molecular packing has occurred via Se⋅⋅⋅π interaction. The staircase-type interlock packing of dimeric molecular arrangement induces sheet-type, herringbone type architecture along crystallographic a axis and ab plane via CH⋅⋅⋅π interactions. Interestingly, the J-type aggregation of 1 in solid state changes to H-type aggregation upon UV-irradiation. Moreover, our spectroscopic findings in solution state reveal H-type of aggregation of 1 in 90 % aqueous THF. We have further demonstrated white light emission in the binary mixture of 1 and 1-pyrenemethanol (2) in 90 % aqueous THF. Our study reveals solvent specific co-assembly of H-aggregated 1 and 2 in 90 % aqueous THF solution, which shows white light emissive properties with the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (0.32, 0.31). The observed white light emission arises mainly due to the combination of red light from H-aggregated 1, blue light from monomeric 2 and green light from excimers of 2.