Novel Hyperbranched Polyfluorenes Containing Electron-Transporting Aromatic Triazole as Branch Unit

Abstract

Linear (P1) and hyperbranched polyfluorenes (PF1-PF5) containing hole-transporting [(4-(9carbazolyl)butoxyphenyl)] side groups and different amounts of branching triphenyl-1,2,4-triazole units (mole fraction: 0-0.22) have been synthesized to investigate hyperbranched structure-optoelectronic property relationship. The hyperbranched polymers have been characterized by NMR, FT-IR, UV-vis, GPC, thermogravimetric analysis, and fluorescence spectroscopy. They show good solubility in common organic solvents such as CHCl 3 , toluene, and CH 2 Cl 2 and exhibit excellent thermal stability with decomposition temperatures higher than 446 °C. Their absorption maxima (λ max ) appear at 349-378 nm (both in CHCl 3 and in the film state), and furthermore, a linear relationship between 1/λ max and 1/(1n triazole ) has been correlated. The structures of PF1-PF5 effectively suppress detrimental excimer formation (∼550 nm) under thermal annealing. However, in PF3-PF5, a new PL emission (∼520 nm) appeared after thermal annealing at 200 °C for 1 h, which was attributed to complexes formed from carbazole and triazole chromophores. Both electrochemical results and MNDO semiempirical calculation suggest that oxidation and reduction start from the side carbazole and branching triazole moieties, respectively. Two layer EL devices (ITO/PEDOT/PF1 or PF2/Al) were fabricated and their optoelectronic properties were investigated. The EL spectra of PF1 and PF2 are similar to their own PL spectra with the maximum brightness being 161 cd/m 2 (at 19.1 V) and 212 cd/m 2 (at 19.0 V), respectively.

Influence of branching architecture on polymer properties

“…By introducing the branching units into the conjugated polymers, the strong π‐π interaction between conjugated chains is weakened, which improves polymer solubility greatly. In the meantime, due to the decrease of conjugated length, the hypochromatic shift of maximum absorption peaks can be observed 68, 69. Compared with linear conjugated polymer in solid state, the maximum emission peak of hyperbranched conjugated polymer shows less red‐shift in the photoluminescence spectra with higher fluorescence quantum efficiency 70.…”

Photocrosslinkable hyperbranched polyfluorenes containing oxadiazole: synthesis, photophysics and electroluminescence

“…The number‐average molecular weight ( M n ) and polydispersity index (PDI) of P5 and P6 are (11 000, 3.54) and (11 000, 5.73), respectively. A larger variation of the PDI is usually observed in the synthesis of hyperbranched polymers,26, 27 which may be the result of the different activities of the functional groups.…”

Synthesis, chemical, and thermoelectric properties of n‐type π‐conjugated polymer composed of 1,2,4‐triazole and pyridine rings and its metal complexes

“…Solvents were dried, distilled, and stored under nitrogen. N , N ′‐Bis[chloro( p ‐bromopyridyl)methylene]hydrazine was synthesized according to the reported manner . Other reagents were purchased and used without further purification.…”