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-9,10dihydroacridine 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.

The synthesis, structural, and photophysical investigations of CuI complexes with a disilanylene-bridged bispyridine ligand 1 are herein presented. Dinuclear (2) and ladder-like (3) octanuclear copper(I) complexes were straightforwardly prepared by exactly controlling the ratio of CuI/ligand 1. Single-crystal X-ray analysis confirmed that dinuclear complex 2 had no apparent π…π stacking whereas octanuclear complex 3 had π…π stacking in the crystal packing. In the solid state, the complexes display yellow-green (λem = 519 nm, Φ = 0.60, τ = 11 µs, 2) and blue (λem = 478 nm, Φ = 0.04, τ = 2.6 µs, 3) phosphorescence, respectively. The density functional theory calculations validate the differences in their optical properties. The difference in the luminescence efficiency between 2 and 3 is attributed to the presence of π…π stacking and the different luminescence processes.

The cell dimensions of pure triclinic 3Ca0.Si02 and monoclinic 3Ca0 -SiOz solid solution (54Ca0. l6SiO2-Al2Oa.Mg0) were determined and the powder diffraction patterns were indexed by the method of precise measurement of the spacings. The lattice constants are expressed in terms of triclinic or monoclinic cells corresponding to pseudo-orthorhombic cells derived from Jeffery's trigonal cell. The apparent lattice constants for pure 3Ca0.Si02 are a = 12.195 a.u., b = 7.104 a&, c = 25.096 a.u., a = 90°, p = 89'44'' y = 89'44'; for 54Ca0.16SiO2.-ALOa.MgO, a = 12.246 a.u., b = 7.045 a.u., c = 24.985 a.u., @ = 90'04'. Precise lattice constants of Jeffery's monoclinic lattice for 54Ca0.-16SiOz-Al,Oa.MgO are derived as a = 33.091 a.u., b = 7.045 a.u., c = 18.546 a.u., @ = 94'08'. High-temperature X-ray patterns showed that pure triclinic 3Ca0 .Si02 transformed to a monoclinic form at about 920'C. and then to a trigonal form at about 970°C. Monoclinic 54Ca0.-16SiO2-AlZO3-MgO transformed to trigonal at about 830'C. These transitions were reversible and reproducible and were accompanied by only slight deformation of the structure forms.

Polymorphic transitions in CasSi06 have been investigated by precise high-temperature X-ray diffractometer measurements and by differential thermal analyses. In addition to change caused by normal thermal expansion, three principal crystallographic transformations take place : atriclinic-@-triclinic (sluggish) in the range 550" to 700°C ; 8-triclinic-monoclinic at 910" f 10°C ; and monoclinic-trigonal at 970" =t 10°C. The sluggish 550" to 700°C reaction alternatively may be interpreted as two separate triclinic-triclinic transitions, accompanied by broad endothermic heat effects at 575" and 675°C.

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