Synthesis and Luminescent Properties of Fluorene Copolymers Bearing DCM Pendants

Abstract

A series of copolymers, poly [(9,9-dioctylfluorene-2,7-diyl)-co-(4-dicyanomethylene-2-methyl-6-[4-(diphenylamino)styryl]-4H-pyran-4′,4′′-diyl)], were synthesized by polymerizing 2,7-bis(4,4,5,5tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene with mixtures of 2,7-dibromo-9,9-dioctylfluorene and 4-dicyanomethylene-2-methyl-6-[bis(4′-bromophenyl)amino]styryl]-4H-pyran (a DCM derivative) by the palladium-catalyzed Suzuki coupling reaction. The copolymers were characterized by molecular weight determination, elemental analysis, 1 H NMR, FT-IR spectroscopy, DSC, TGA, UV-vis spectroscopy, and photoluminescence (PL) and electroluminescence (EL) spectroscopy. The copolymers showed two absorption peaks at 380 and 485 nm, and the long-wavelength absorption increased with increasing the fraction of the DCM comonomer. The PL spectra of copolymers in chloroform solution displayed emission from both the main chain (420 nm) and DCM units (620 nm). In the solid state, however, PL spectra of copolymers showed only the long wavelength red emission at 620 nm with no trace of emission from the main chain, which implies a facile exciton migration or energy transfer to the lower energy sites from the fluorene part to the DCM part. This results in emission of only the red light originating from the latter segments. A study on time-resolved PL rise and decay of the polymers clearly supports the energy transfer mechanism. Light-emitting diode (LED) devices were fabricated to have the configuration of ITO (indiumtin oxide)/PEDOT/polymer/Li:Al alloy. EL spectra of the devices showed only red emissions as observed in the PL spectra of the polymers' thin films. EL efficiency decreased with increasing DCM contents. When a tris(8-hydroxyquinolinato)aluminum (Alq 3) layer was inserted between the emitting polymer layer and the cathode to make the ITO/PEDOT/polymer/Alq3/Li:Al alloy configuration, the device efficiencies became much higher (∼10 -2 %) than those (5 × 10 -5 -5 × 10 -3 %) of single-layer devices.

Synthesis, Characterization and Photophysical Properties of DCM‐Based Light‐Harvesting Dendrimers

“…[19] New derivatives of DCM for device applications were published by Jung et al [20] Jin and coworkers reported the synthesis and luminescent properties of fluorene copolymers bearing DCM pendants. [21] Recently, Choi and co-workers reported the red-emitting phenothiazine dendrimers encapsulated with DCM derivatives. [22] So far, light harvesting molecule of pyrene/DCM combination has not been reported.…”

Highly efficient and stable blue‐light‐emitting copolyfluorene consisting of carbazole, oxadiazole, and charge‐trapping anthracene groups

“…The thermal decomposition temperature ( T d ) and glass transition temperature ( T g ) of P1 is 406 °C (∼5% loss) and 145 °C, as examined by thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). The T g of P1 is much higher than 97 °C for poly(9,9‐dioctylfluorene) (PFO) 42. The high T g is conducive to reducing crystallization and to retaining long‐term morphological stability when applied as an active layer in EL devices 43…”

Polyfluorenes

“…Furthermore, green light from BT units was also observed. [126]. In solid state, only a long-wavelength emission at 620 nm originating from the DCM moieties is observed.…”