Abstract
Alternating copolymerization of 9,9-dihexyl-2,7-dibromofluorene, N-hexyl-2,7-dibromocarbazole (HCz) with diethynyldimethylsilane, diethynyldiphenylsilane, has been investigated using Sonogashira coupling reaction. Photophysical properties of the resulting copolymers were investigated with UV-Vis absorption and photoluminescence spectroscopy. All the copolymers in chloro-form solution showed absorption peaks at 270 - 280 nm with shoulder peaks at around 380 nm derived from π-π* transition or intra-molecular charge transfer through σ-π moiety, respectively. The chloroform solutions of the copolymers showed broad emission peaks at 415 - 425 nm. The emission wave lengths of the copolymers in the solid state (cast film) detected at 360 - 385 nm were remarkably blue-shifted in comparison with those in the chloroform solutions. Hydrosilylation reaction of the copolymers with 1,4-bis(dimethylsilyl)benzene yielded networked copolymers soluble in chloroform, indicating formation of branching polymers. The chloroform solutions of the HCz-based networked copolymers showed bimodal emission derived from new highly energy states in the σ-π conjugation.
Highlights
A number of conjugated polymers have been developed due to their attractive features, especially phot- and electro-luminescence
The fluorene or carbazole-based alternating copolymers containing Si and ethynylene units in the main chain were successfully synthesized by Sonogashira coupling reaction of dibromo-fluornene or carbazole (HFl, HCz) and diethynylene Si compounds (EMS, EPS)
The resulting copolymers showed bimodal absorption peaks and broad emission peaks in the chloroform solutions derived from the intramolecular charge transfer through the σ-π moiety
Summary
A number of conjugated polymers have been developed due to their attractive features, especially phot- and electro-luminescence. Masuda et al synthesized poly(phenylene-ethnylene) containing Si atom in the main chain [4] They observed the emissions of the polymers derived from π-π* transition of the π-conjugation but intramolecular charge transfer through σ-π conjugation. Incorporation of Si and unsaturated vinylene units in the main chain of the conjugated polymers was effective to improve solubility in the organic solvents. The fluoreneand carbazole-based alternating copolymers containing Si-vinylene units in the main chain showed both the blue-shift and red-shift in the absorption and luminescence peaks depend on the state of the copolymers. Ishikawa et al reported synthesis of the σ-π conjugated network copolymers by a crosslinking of poly[(silylene)diethnylene] with 1,4-bis(methylphenylsilyl)benzene using a hydrosilylation reaction [19] This method is usable to synthesize the network polymers with the σ-π conjugation from the fluorene- and carbazole-based copolymers having Si-ethynlene units in the main chain synthesized in this report. We synthesize the network polymers by a hydrosilylation reaction of the obtained copolymers with 1,4-bis(dimethylsilyl)benzene (DMSB), and study the effect of the networking on the photophysical properties in comparison with the original linear copolymers
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