Jianglin Fang

Self-assembled hierarchical structure evolution of azobenzene-containing linear-dendritic liquid crystalline block copolymers

In this paper, the phase behaviors and self-assembled structures of a series of liquid crystalline linear-dendritic block copolymers (LDBCs) in the bulk state have been systematically investigated in combination with DSC, POM, SAXS, WAXS, and TEM. The LDBCs consist of a linear poly(ethylene glycol) (PEG) block (degree of polymerization, DP = 49) and dendritic polyamidoamine (PAMAM) segments of generation G0 to G3, functionalized with photoactive azobenzene mesogenic units bearing an octyloxy tail and a flexible ten-methylene spacer (AZO). An unprecedented hierarchical structure evolution with increasing dendron generation has been demonstrated for this series of azobenzene-containing LDBCs in bulk. Well-defined lamellar structures are formed for liquid crystalline LDBCs of G0, G1, and G2 with only a slight change in layer spacing between 12.2 and 13.0 nm. A simple lamellar structure is generated by mPEG-G0-(AZO)2, while tetragonal-within-lamellar and lamellar-within-lamellar hierarchical structures are created in mPEG-G1-(AZO)4 and mPEG-G2-(AZO)8, respectively, due to further suborganization between PAMAM and AZO segments within the dendritic blocks. For the highest generation copolymer investigated in this work, mPEG-G3-(AZO)16, the structure changes dramatically from lamellar for lower generations into rectangular columnar with lattice parameters a = 8.5 nm and b = 6.5 nm or higher temperature disordered columnar mesophases. The introduction of the alkyloxy tail in the azobenzene mesogenic unit is of crucial importance for constructing such hierarchical structures. Moreover, those complex lamellar mesophases transform into micellar or network cubic structures upon cooling to ambient solidification temperature with PEG crystallization showing a complete inverse phase change tendency in virtue of the curvature effect as a result of the specific linear-dendritic architecture. Very interestingly, the films of azobenzene-containing liquid crystalline LDBCs exhibit generation/morphology dependent photophysical characteristics, which may afford a convenient way for designing and fine-tuning novel optical storage materials.

Cyclic polymers with pendant triphenylene discogens: convenient synthesis and topological effect on thermotropic liquid crystal behavior and fluorescence enhancement

Novel discotic liquid crystalline cyclic polymers prepared through RAFT polymerization and intrachain azide–alkyne click cyclization, exhibit fully inhibited or significantly weakened bulk columnar ordering with increased molecular weight or shortened spacer length, while exhibiting remarkably enhanced fluorescence emission in solution as a result of the cyclic topological constraint effect.

Formation of persistent ordered lamellar mesophases in azobenzene-containing silver thiolates and their application in the controlled synthesis of silver nanomaterials

Metal thiolates have aroused intensive interest mainly due to their precursor-based preparation of nanostructured metal or metal chalcogenides. In this paper, a series of azobenzene-containing thiol ligands with different length alkoxy tails and their corresponding silver thiolates AgS–C10H20–Ph–NN–Ph–OCnH2n+1 with n = 1, 6, 8, 12, have been successfully synthesized, and their thermal properties and phase behavior have been systematically investigated by differential scanning calorimetry (DSC), variable-temperature SAXS/WAXS and temperature dependent FTIR. By introducing azobenzene mesogen for the first time into the silver thiolates, ordered lamellar liquid crystalline mesophases persisting throughout a higher temperature have been achieved derived from their specific orthorhombic crystalline structures, which are in sharp contrast to the micellar or hexagonal columnar mesophases reported for silver alkane thiolates with a longer aliphatic alkyl chain AgSCmH2m+1 (m ≥ 12) owing to the interplay of azobenzene mesogen π–π stacking and the inorganic skeleton binding of a Ag–S slab. Furthermore, the intermediate nanoparticles formation and silver nanodisks preparation through an in situ thermolytic reaction based on such mesogenic precursors have been demonstrated in principle. As a kind of functional metallomesogen precursor the silver mesogenic thiolates with persistent ordered lamellar mesophases provide an ideal two-dimensional (2D) confined environment for the investigation of a layered-precursor-to-lamellar-nanomaterial (LPLM) mechanism of solventless thermolysis and the fascinating controlled preparation of variant 2D shaped metal or metal sulfide nanomaterials.

Competition and compromise between discotic and calamitic mesogens in triphenylene and azobenzene based shape-amphiphilic liquid crystals

Clarifying the relationship and interplay between disc-like (discotic) and rod-like (calamitic) mesogens is highly appealing. In this article, a series of novel disc-rod shaped amphiphilic liquid crystalline dimers and side-chain polymers based on typical discotic triphenylene (TP) and calamitic azobenzene (AZO) mesogens have been well synthesized and systematically investigated. It was found that lamello-columnar mesophases were characteristic for disc-rod hybrids and bridge the lamellar and columnar phases typical for calamitic or discotic mesogens alone. For the TP6 based hybrid dimers with peripheral hexyloxy substituents, the phase structure evolves from a sequence of lamello-columnar mesophases Colr/L and slim ColSr/L for dimers TP6–AZO6 and TP6–AZO8 with shorter hexyloxy or octyloxy tails attached on AZO, to a single Colr/L mesophase persisting to lower temperature for TP6–AZO12 and TP6–AZO16 with longer dodecyloxy or hexadecyloxy tails. With the extension of TP peripheral substituents to decyloxy, although TP10–AZO12 exhibits only a stable lamello-columnar mesophase Colr/L, the TP10–AZO6 represents an ideal sample of majority discotic moieties and just the right calamitic fraction, which demonstrates a fascinating phase transformation from a simple lamellar phase to a disordered oblique columnar phase Colob-d through an intermediate lamello-columnar mesophase Colr/L. Although the methacrylate monomer derived from the hybrid TP6–AZO10 exhibits similar lamello-columnar mesophase Colr/L, the corresponding polymer displays only a simple lamellar phase due to the constraint of the polymethacrylate backbone. The elucidation of complex self-assembly behavior and in-depth understanding of the competition and compromise between different shape aromatic moieties in disc-rod shaped amphiphiles is of crucial importance for clarifying the aromatic interactions involved in complex biological systems and guiding molecular design of advanced organic materials for various optoelectronic applications.

Self-assembled helical columnar superstructures with selective homochirality

Electron donor–acceptor (EDA) complexes of triphenylene (TP) based side-chain discotic liquid crystalline polymers doped with chiral acceptors exhibit a remarkable supramolecular polymer effect upon reaching a critical doping amount, complying with the discrete columnar stack (DCS) based modular assembly mechanism. Furthermore, selective left- or right-handed homochirality determined by the enantiomeric nature of chiral dopants has been achieved, with a helical polymer backbone surrounded by chiral supramolecular columns through modular assembly between the chiral dopant and DCS subunits, revealing a strong circular dichroism (CD) activity reminiscent of the fascinating hierarchically assembled superstructure of tobacco mosaic virus (TMV). Such polymeric EDA stoichiometric complexation and generation of single-handedness provides inspiring insight into and guidance for constructing various chiral functional materials via non-covalent interactions in a facile way, and also enhances in-depth understanding of the origin of biological helical structures and chiral basis of life.

Highly efficient luminescent side-chain polymers with short-spacer attached tetraphenylethylene AIEgens via RAFT polymerization capable of naked eye explosive detection

Tetraphenylethylene (TPE) is one of the well-known typical aggregation-induced emission (AIE) luminogens (AIEgens) and TPE-containing polymers possess excellent processing properties which facilitates the fabrication of various AIE systems and devices. For AIE active side-chain polymers, increasing the fluorescence quantum yield through suitable molecular design is very appealing. In this work, we present the well-controlled synthesis of a series of TPE polyacrylate side-chain polymers of Pm with short spacers with methylene number m = 0–5 via RAFT polymerization. All the obtained polymers exhibit typical and strong AIE characteristics in THF/H2O solution mixtures and in solid state films. In particular, greatly enhanced fluorescence emission is achieved with reduced spacer lengths, and further significant improvement achieved through annealing, which is ascribed to the restriction of intramolecular motions (RIM) and the blocking of the non-radiative channels due to overcrowding and confinement thanks to the strong positive coupling effect and the jacketing effect of side-chain polymers with very short spacers. The quantum yields of 34.4%, 32.0% and 31.4%, respectively, for the polymer films P0, P1 and P2 are several times higher than those of homologous polymers with longer spacers reported in the literature. Based on these TPE side-chain polymers of very short spacers, a simple, economic and visual method for detection of the explosive 2,4,6-trinitrotoluene (TNT) is demonstrated. Therefore, a facile approach and feasible strategy of simply adopting very short spacers for side-chain AIE active polymer preparation to significantly enhance the luminescence efficiency has been properly established and proposed, which may provide guidance and have a wealth of implications for the rational design and preparation of highly efficient luminescent AIE polymer materials.

Toward well-organised ionic discotic liquid crystals via versatile supramolecular approach

ABSTRACT Various ordered structures of crystalline three-dimensional (3D) cubic, 2D columnar or 1D lamellar mesophases have been facilely achieved through host–guest interactions of electrically neutral host tris(18-crown-6)triphenylene and guest potassium sulfonates with alkyl tails of variant number and length. The convenient construction of functionalised ionic complexes and the flexibility of such a supramolecular approach offer a wide variety of possibilities to prepare various ordered functional soft materials, especially those in their 2D ordered columnar liquid crystalline mesophases may serve as promising electron and ion dual-channel transport organic electronic materials. Graphical Abstract

Probing into dimension and shape control mechanism of copper(I) sulfide nanomaterials via solventless thermolysis based on mesogenic thiolate precursors

Nanostructured materials of various shape and dimension have aroused intensive interests, among which copper(I) sulfide (Cu2S) nanomaterials are of particular prominence. In this work, various nanostructured Cu2S have been facilely prepared via solventless thermolysis, with well-controlled shape and dimension determined by and inherited from the layered structures of the azobenzene-containing single-source copper thiolate mesogenic precursors. The precursors with longer alkyl tails exhibit highly ordered layered liquid crystalline mesophases and retain persistent order up to temperatures beyond the clearing points. Under non-vacuum inert atmosphere or with further elevated temperature, large undulations of the constrained lamellar space result in significantly enhanced diffusion, migration and mass transfer, thus leading to the morphologies changing from one-dimensional (1D) ultrathin nanowires into thickened nanorods then to discrete 2D nanodisks. Based on a variety of modern techniques, especially in situ variable-temperature small angle X-ray scattering (SAXS), an extended universal “layered-precursor to lamellar-nanomaterial” (LPLM) mechanism has been proposed to account for the structural evolution of Cu2S nanomaterials. Our findings provide a novel pathway with clearer mechanism for well-controlled preparation of metal chalcogenides of various dimension and shape. In particular, the ultrathin Cu2S nanowires are anticipated to serve as fascinating semiconducting materials for various promising device applications.