Chiral Polyfluorene Derivatives: Synthesis, Chiroptical Properties, and Investigation of the Structure−Property Relationships

Tunable circularly polarized electroluminescence behaviors from chiral co-assembled conjugated liquid crystal polymers

Chiral co-assembly strategy has proven effective in increasing the dissymmetry factor (gEL) of the emitting layers (EMLs) in circularly polarized organic light-emitting diodes (CP-OLEDs). Therefore, it is crucial to investigate the molecular structures that facilitate chiral co-assembly for further amplification of circularly polarized electroluminescence (CP-EL) signals. In this study, three types of achiral conjugated liquid crystal (LC) polymers (PFPh, PFNa and PFPy) and chiral binaphthyl-based polymer inducers (R/S-FO) were synthesized to construct corresponding chiral co-assemblies (R/S-FO)0.1-(PFPh/Na/Py)0.9 as EMLs for CP-OLEDs through strong intermolecular π-π stacking interactions. Interestingly, these resulting chiral co-assembled EMLs exhibited tunable CP-EL behaviors caused by the different conjugation linkers of LC polymers. Among them, the deep blue devices based on (R/S-FO)0.1-(PFNa)0.9 emitted the strongest CP-EL signals (|gEL| = 0.014, Lmax = 3039 cd m-2, CEmax = 1.16 cd A-1). It is attributed to the formation of ordered helical nanofibers facilitated by the excellent intermolecular compatibility due to the same naphthyl moieties in PFNa and R/S-FO. This study provides novel perspectives for developing high-performance CP-EL materials in chiral co-assembly systems.

Optically Programmable Circularly Polarized Photodetector

The detection of circularly polarized light (CPL) has aroused wide attention from both the scientific and industrial communities. However, from the optical activity of the chiral layer in the conventional CPL photodetectors, the sign inversion property is difficult to be achieved. As a result, great challenges arise during the preparation of miniaturized and integrated devices for tunable CPL detection applications. Along these lines, in this work, by taking advantage of the CPL-induced chirality characteristics of the achiral poly(9,9-di-n-hexylfluorene-alt-benzothiadiazole) (F6BT) and the good crystalline and electrical properties of the poly(3-hexylthiophene) (P3HT) film, an optically programmable CPL photodetector was fabricated. Interestingly, the device exhibited excellent discrimination between left- and right-handed CPL, while the maximum anisotropy factor of responsivity was 0.425. On top of that, the rigorously controlled chirality of the F6BT and the capability to be switched by the handedness of CPL was leveraged to realize the switchable detection of both L-CPL and R-CPL. Furthermore, a CPL photodetector array was fabricated, and the image processing and cryptographic characteristics were demonstrated. The proposed device configuration can find application in various scientific fields, including photonics, emission, conversion, or sensing with CPL but also is anticipated to play a key role for imaging and anticounterfeiting applications.

Solvent-sensitive circularly polarized luminescent compounds bearing a 9,9′-spirobi[fluorene] skeleton

Chiral 9,9′-spirobi[fluorene] derivatives with a donor–π–acceptor system were prepared and found to exhibit solvent-sensitive circularly polarized luminescence.

Control over chiroptical and electronic properties of poly(9,9′-bifluorenylidene) bearing chiral side chains

The introduction of chiral side chains at peripheral positions of the 9,9′-bifluorenylidene moiety causes an efficient bias to its dynamic molecular helicity, which helps control the chiroptical and electronic properties of resultant polymers.

Solvent polarity effects on supramolecular chirality of a polyfluorene-thiophene copolymer

This study demonstrates the supramolecular chirality control of a conjugated polymer via solvent polarity. We designed and synthesized a chiral polyfluorene-thiophene copolymer having two different chiral side chains at the 9-position of the fluorene unit. Chiral cyclic and alkyl ethers with different polarities were selected as the chiral side chains. The sign of the circular dichroism spectra in the visible wavelength region was affected by the solvent system, resulting from the change of supramolecular structure. The estimation of the solubility parameter revealed that the solubility difference of the side chains contributed to the change of the circular dichroism sign, which was also observed in spin-coated films prepared from good solvents having different polarities.

Pitch and Handedness of the Cholesteric Order in Films of a Chiral Alternating Fluorene Copolymer

The molecular organization in thermally annealed films of poly(9,9-bis((S)-3,7-dimethyloctyl)-2,7-fluorene-alt-benzothiadiazole) is investigated using polarized light. Measurement of linear polarization in transmission and reflection as a function of layer thickness and orientation directly show a left handed cholesteric organization with a pitch length of 600 nm. Results are corroborated by measurements of circularly polarized reflection and generalized ellipsometry and are compared to calculations of the optical properties based on the Maugin–Oseen–DeVries model. For wavelengths near the lowest allowed optical transition, light with the same handedness as the cholesteric arrangement (left) is found to be reflected and transmitted with a probability higher than right circularly polarized light. The high transmission for left polarized light is interpreted as an optical manifestation of the Borrmann effect.