Second-Order Nonlinear Optical Dendrimers and Dendronized Hyperbranched Polymers.

Second-order nonlinear optical (NLO) dendrimers with a special topological structure were regarded as the most promising candidates for practical applications in the field of optoelectronic materials. Dendronized hyperbranched polymers (DHPs), a new type of polymers with dendritic structures, proposed and named by us recently, demonstrated interesting properties and some advantages over other polymers. Some of our work concerning these two types of polymers are presented herein, especially focusing on the design idea and structure-property relationship. To enhance their comprehensive NLO performance, dendrimers were designed and synthesized by adjusting their isolation mode, increasing the number of the dendritic generation, modifying their topological structure, introducing isolation chromophores, and utilizing the Ar-ArF self-assembly effect. To make full use of the advantages of both the structural integrity of dendrimers and the convenient one-pot synthesis of hyperbranched polymers, DHPs were explored by utilizing low-generation dendrons as big monomers to construct hyperbranched polymers. These selected works could provide valuable information to deeply understand the relationship between the structure and properties of functional polymers with dendritic structures, but not only limited to the NLO ones, and might contribute much to the further development of functional polymers with rational design.

Functional hyperbranched polymers with advanced optical, electrical and magnetic properties.

As one kind of important functional material, those with advanced optical, electrical and magnetic characteristics have attracted increasing attention due to their essential and irreplaceable role in the daily life of humans. In particular, optical, electrical and magnetic hyperbranched polymers (HBPs) exhibit some unique properties, partially derived from their highly branched topological structures. This review summarizes the recent progress in the field of functional HBPs and their application in optics, electronics and magnetics, including light-emitting polymers, nonlinear optical materials, chemosensors, solar cells, magnetic materials, etc., and also gives some outlooks for further exploration in this field at the end of this paper.

A new approach to prepare efficient blue AIE emitters for undoped OLEDs.

Two aggregation-induced emission active luminogens (TPE-pTPA and TPE-mTPA) were successfully synthesized. For comparison, another six similar compounds were prepared. Because of the introduced hole-dominated triphenylamine (TPA), fluorene groups with high luminous efficiency, and unconjugated linkages, the π conjugation length of the obtained luminogens is effectively restricted to ensure their blue emission. The undoped organic light-emitting diodes based on TPE-pTPA and TPE-mTPA exhibited blue or deep-blue emissions, low turn-on voltages (3 V), and high electroluminescence efficiencies with Lmax, ηC,max, and ηP,max values of up to 26,697 cd m(-2), 3.37 cd A(-1), and 2.40 Lm W(-1).

A new low-bandgap polymer containing benzene-fused quinoxaline: significantly enhanced performance caused by one additional benzene ring.

Two new alkoxy-substituted quinoxaline (Qx)-based copolymers, PBDTQx and PBDTPz, are designed and synthesized. The only difference between these two polymers is that two methyl groups of the Qx are replaced by one additional fused benzene ring. The UV-Vis absorptions, thermal stability, energy levels, field-effect carrier mobility, and photovoltaic characteristics of the two copolymers are systematically evaluated to understand the relationships between the polymer structure at the molecular level and the photovoltaic performances. Photovoltaic cells based on the PBDTPz with a structure of ITO/PEDOT:PSS/Polymer:PC(71) BM/PEO/Ca/Al exhibit a promising efficiency of 4.40%, while that of PBDTQx is relatively much poorer.

Janus second-order nonlinear optical dendrimers: their controllable molecular topology and corresponding largely enhanced performance.

A new type of Janus dendrimers, consisting of two different side dendrons with the dipole orientation of the second-order nonlinear optical (NLO) chromophore moieties partially in a non-centrosymmetric direction, was intelligently designed and synthesized in order to enhance the macroscopic NLO performance and break through the limitation of NLO efficiency in the current molecular topological structure of azo chromophore-based polymers. This kind of Janus dendritic structure was constructed by the combination of convergent and divergent methods, with the utilization of a powerful "click chemistry reaction". The obtained three dendrimers, D-13N, D-17N and D-21N, show very high NLO performance, especially the dramatically enhanced NLO coefficient of 299 pm V-1 for D-13N, which is the highest value ever reported for polymers containing a simple azo chromophore. The new dendrimers provide a clear structure-properties relationship between high NLO efficiency and the controllable molecular topology with the non-centrosymmetrical alignment of dipole orientation, thus opening up a new avenue for the further development of NLO dendrimers with high performance and more importantly providing some clues for the rational design of functional dendrimers with controllable molecular topology.

Different Effect of the Additional Electron-Withdrawing Cyano Group in Different Conjugation Bridge: The Adjusted Molecular Energy Levels and Largely Improved Photovoltaic Performance.

Four organic sensitizers (LI-68-LI-71) bearing various conjugated bridges were designed and synthesized, in which the only difference between LI-68 and LI-69 (or LI-70 and LI-71) was the absence/presence of the CN group as the auxiliary electron acceptor. Interestingly, compared to the reference dye of LI-68, LI-69 bearing the additional CN group exhibited the bad performance with the decreased Jsc and Voc values. However, once one thiophene moiety near the anchor group was replaced by pyrrole with the electron-rich property, the resultant LI-71 exhibited a photoelectric conversion efficiency increase by about 3 folds from 2.75% (LI-69) to 7.95% (LI-71), displaying the synergistic effect of the two moieties (CN and pyrrole). Computational analysis disclosed that pyrrole as the auxiliary electron donor (D') in the conjugated bridge can compensate for the lower negative charge in the electron acceptor, which was caused by the CN group as the electron trap, leading to the more efficient electron injection and better photovoltaic performance.

Largely blue-shifted emission through minor structural modifications: molecular design, synthesis, aggregation-induced emission and deep-blue OLED application.

By simply introducing additional groups with different size and conjugation degree to the 2,2'-positions of BTPE, four BTPE derivatives are prepared which give blue or deep-blue EL emissions when used as emitters in non-doped OLEDs, as the result of the tuned dihedral angles of the biphenyl cores (up to ~89°), providing a new approach to design AIE luminogens with blue and deep-blue emissions.

Attempt to improve the performance of pyrrole-containing dyes in dye sensitized solar cells by adjusting isolation groups.

Four new pyrrole-based organic sensitizers with different isolation groups were conveniently synthesized and applied to dye sensitized solar cells (DSCs). The introduction of isolation group in the side chain could both suppress the formation of dye aggregates and electron recombination. Especially, when two pieces of D-π-A chromophore moieties shared one isolation group to construct the "H" type dye, the performance was further improved. Consequently, in the corresponding solar cell of LI-57, a short-circuit photocurrent density (Jsc) was tested to be 13.85 mA cm(-2), while 0.72 V for the open-circuit photovoltage (Voc), 0.64 for the fill factor (FF), and 6.43% for the overall conversion efficiency (η), exceeding its analogue LI-55 (5.94%) with the same isolation group. The results demonstrated that both the size (bulk and shape) and the linkage mode between the D-π-A chromophores and the isolation groups, could affect the performance of sensitizers in DSCs in a large degree, providing a new approach to optimize the chemical structure of dyes to achieve high conversion efficiencies.

New fluorescent and colorimetric probe for cyanide: direct reactivity, high selectivity, and bioimaging application.

Taking advantage of the special nucleophilicity of cyanide, a new ratiometric fluorescent and colorimetric probe (Coum-1) was designed by tuning the π-conjugated bridge to affect the intramolecular charge transfer efficiency. Upon the addition of CN(-) anion, the probe displayed very large blue-shift in both fluorescence (90 nm) and absorption (90 nm) spectra, with the detection limit of 800 nM. Other anions gave nearly no interference. Furthermore, Coum-1 was successfully applied to the fluorescent microscopic imaging for the detection of CN(-) in HeLa cells.

Bipolar AIE-active luminogens comprised of an oxadiazole core and terminal TPE moieties as a new type of host for doped electroluminescence.

For the first time, two bipolar AIE-active luminogens (Oxa-pTPE and Oxa-mTPE) constructed from tetraphenylethene and oxadiazole were utilized as fluorescence host materials in sky-blue doped OLEDs and exhibited high efficiencies with L(max), η(C,max), η(P,max) and η(ext,max) of 10,070 cd m(-2), 9.79 cd A(-1), 9.92 Im W(-1) and 5.0%, respectively, broadening the scope for the utilization of AIE materials in the optoelectronic field.