Highly efficient blue light-emitting polymer containing a Benzo[b]naphtho [1,2-d]thiophene -S,S-dioxide unit

The dibenzothiophene-S,S-dioxide (SO) possess strong but unmatched electron-withdrawing ability when connected to a normally used donor. Here, to lower its electron-withdrawing ability, we synthesized a benzo[b] naphtho[1,2-d]thiophene-S,S-dioxide (NSO) electron-deficient acceptor by using a naphthalene ring to replace one of the benzene rings in the SO unit. The copolymers PPF-NSs and PPF-NSOs were synthesized by introducing the NSO and benzo[b]naphtho[1,2-d] thiophene (NS) unit into polyfluorene backbone. A systematic study was presented based on the copolymers from the aspect of theoretical calculation, photophysical properties, electrochemical properties, and electroluminescent properties. For the PPF-NSs film, intermolecular energy transfer should be the main mechanism of photoluminescence. Whereas, intramolecular charge transfer played the main role in the photoluminescence mechanism for PPF-NSOs film due to the existence of the strong electron-deficient group (NSO). The PPF-NSOs acquired superior blue emission with maximum luminous efficiency (LEmax) of 8.16 cd A-1 and a CIE of (0.16, 0.25) at a low acceptor concentration of 3%, while the copolymer (PPF-NS1) based on energy transfer also achieved a satisfactory performance with LEmax of 5.20 cd A-1 and a CIE of (0.17, 0.18).

Automated summary

A benzo[b] naphtho[1,2-d]thiophene-S,S-dioxide (NSO) electron-deficient acceptor was synthesized to lower the electron-withdrawing ability. The copolymers PPF-NSs and PPF-NSOs were studied, and it was found that intermolecular energy transfer was the main mechanism of photoluminescence for PPF-NSs, while intramolecular charge transfer played the main role for PPF-NSOs. PPF-NSOs showed superior blue emission at a low acceptor concentration, while the energy transfer-based copolymer PPF-NS1 also achieved satisfactory performance.