Dibenzosilole-based polymers

The optical absorption spectra of dibenzosilole-based polymers 618-620 have absorption maxima that are blue shifted compared to those of dithienylsilole 615-617. The absorption maximum for homopolymer 618 occurs at 377 nm, corresponding to the largest n—n transition energy in the silole-based polymer series. 

Poly(dibenzosilole)s are a relatively new class of compounds for the area of organic electronic materials. Poly(dibenzosilole)s are not easily oxidised and have advantages of solubility and processibility over other polyfluorene analogues, such as carbazoles, dibenzophosphole oxides and dibenzothiophene dioxides. Several groups have already incorporated poly(dibenzosilole)s in the latest organic electronic devices such as OLEDs, OFETs and OSCs and have found improved performance over similar polyfluorene-based devices. With continual advancement in their synthesis, dibenzosilole-based polymers are set to match the popularity of polyfluorenes in organic electronic materials. 

Polymers 619 and 620 exhibit two absorption maxima located at 444 and 471 nm for 619 and 473 and 503 nm for 620. These transitions likely correspond to predominantly local transitions of the constituent dibenzosilole and mono/bithiophene copolymer building blocks. The absorption maxima of polymer 618-620 cast as thin films are 401 nm (618), 484 nm (619), and 493 nm (620). The fluorine-based copolymers exhibit maxima at 427 nm in solution and 440 nm as a thin film for 621 and 456 nm in solution (with strong shoulder at 502 nm) and 460 nm as a thin film for 622. Dibenzosilole-based copolymers 619 and 620 exhibit significant bathochromic shifts of ca. 30-50 nm compared to the fluorine-based polymers 621 and 622. 

Abstract Poly(dibenzosilole)s are an emerging class of polymers with similar optoelectronic properties to polyfluorenes. With increased stability towards oxidation, several poly(dibenzosilole)-based devices, such as light emitting diodes, have shown improved performance over their polyfluorene counterparts. As a consequence of reduced conjugation in the polymer chain, some poly(dibenzosilole)s have high triplet excited state energies, which make them suitable hosts for blue triplet emitters in electrophosphores-cent devices. 

Polymer LEDs with copolymers containing dibenzosiloles have been reported in the literature [39,42]. By varying the 3,6-dibenzosilole content in a fluorene-based polymer, superior colour purity and optimum external quantum and luminous efficiencies were obtained (Fig. 5) [39]. Compared to polyfluorene, these copolymers are also stable to thermal annealing. Similar results were reported for a 2,7-dibenzosilole-co-3,6-dibenzosilole polymer [42]. 

We will provide a class of low bandgap polymers applied in BHJ PSCs that are synthesized by Suzuki polycondensation. This section cannot possibly cover all these different polymers. Emphasis will be placed upon important classes of conjugated polymers based on bridged phenylenes, for example poly(2,7-fluorene), poly(2,7-carbazole), and poly(2,7-dibenzosilole) based D-A conjugated polymers. 

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