ATRP Synthesis of Oligofluorene-Based Liquid Crystalline Conjugated Block Copolymers

Abstract

A series of well-defined conjugated-liquid crystalline (LC) block copolymers containing oligofluorene and side-chain liquid crystalline polymers with cyanobiphenyl moieties were successfully synthesized by atom transfer radical polymerization. The block copolymers were prepared with number-averaged molecular weights (M n) ranging from 8000 to 16 000 and narrow molecular weight distribution less than 1.20. The chemical structures of these block copolymers were confirmed by 1H NMR, 13C NMR, and FTIR studies. All of the block copolymers exhibited the smectic mesophase as illustrated by differential scanning calorimetry, polarized optical microscopy, and wide-angle X-ray diffraction. A bilayer structure of mesogens was formed in the smectic layer of block copolymers with a thickness of 3.5 nm. The isotropization of the smectic phase increased with the molecular weight and leveled off at M n = 14 000. The optical properties of these block copolymers in solution and solid-films were investigated comparatively by UV spectroscopy, photoluminescence, and photoluminescent excitation characterization. The results suggest that energy transfer from the LC mesogens to the conjugated oligomer occurs both in dilute solution and in the solid state, which was more efficient in solid state due to higher local chromophore density.

Synthesis of push-pull chromophores including an N-[4-(4-methoxyphenoxy)butyl]carbazole fragment

“…Yield 68%, mp 43-45°C (46-47°C [16,17]). 1 Н NMR spectrum, δ, ppm: 1.90 quintet (2Н, CH 2 СН 2 Br, J 6.6 Hz), 2.05 quintet (2Н, OСН 2 CH 2 , J 6.3 Hz), 3.47 t (2Н, СН 2 Br, J 6.3 Hz), 3.75 s (3Н, ОMe), 3.93 t (2Н, ОСН 2 , J 6.3 Hz), 6.81 s (4Н, C 6 H 4 ).…”

Liquid crystalline conjugated polymers and their applications in organic electronics

“…In many ways, oligomers own better optical properties and are easier to manipulate compared with their corresponding polymers. Several conjugated oligomers with LC properties have been synthesized to study their photo-physical and self-assembled properties, including oligo(p-phenylenevinylene) (OPV), [65][66][67][68][69][70][71][72][73][74] oligofluorene, [75][76][77][78][79][80] and oligo(p-phenyleneethynylene).…”

Influence of processing conditions on mechanical properties of blends of styrenic block copolymer and poly(phenylene oxide): Miscibility and microdomain size

“…The morphology of this nanoscale microstructure mainly depends on the interaction parameter between the incompatible blocks (χ), the degree of polymerization, the block composition of copolymers, and the molecular architecture . Importantly, the thermal history and processing conditions also have a great influence on the microstructure …”