Synthesis of dithienogermole-containing oligo- and polysilsesquioxanes as luminescent materials

Abstract

Dithienogermole (DTG)-containing oligo- and polysilsesquioxanes were prepared by hydrolysis/condensation of DTGs bearing one (DTG1) or two trialkoxysilyl group(s) (DTG2). The reaction of DTG1 gave a cage-type octasilsesquioxane with eight DTG groups at the edges (DTG1-POSS) as a viscous oil, whereas the reaction of DTG2 yielded a network polymer (DTG2-PSQ) as a self-standing film. DTG1-POSS showed a photoluminescence (PL) quantum yield (Φ) of 56% in THF. This value was as high as that of DTG1 (Φ = 58%), in spite of the accumulation of DTG units in the molecule, as characteristics of the POSS structure. The PL of DTG1-POSS in THF was suppressed by contact with nitrobenzene, showing the potential of DTG1-POSS for sensing nitroaromatic explosives. Polymer DTG2-PSQ exhibited a relatively low Φ of 2% as a film, but Φ was improved to 38% by copolymerization with trimethoxymethylsilane. DTG2 was also copolymerized with a trimethoxysilyl-substituted carbazole derivative (CzS) to provide polysilsesquioxanes with DTG and carbazole units, which showed efficient photo-energy transfer from carbazole to DTG in the films. Similar copolymerization of DTG2 with CzS in the presence of poly(9-vinylcarbazole) provided a composite material with hole-transporting electroluminescence properties, applicable in multi-layered organic light emitting diodes.