Hongmin Huang

Synthesis and spectroscopic properties of a series of hyperbranched conjugated molecules with 1,3,5-triphenylbenzene as cores

A series of conjugated hyperbranched molecules with 1,3,5-triphenylbenzene rings as cores and with different connecting groups have been synthesized. Their structures were characterized by FTIR, 1H-NMR and 13C-NMR. These molecules exhibit good solubility and film-forming ability. In particular, they have high thermal stability (TID > 350 °C). The spectroscopic properties of these molecules were studied both in solution and as spin-coated films. The twisted intramolecular charge transfer (TICT) state was observed in hyperbranched molecules containing triphenylamine as the connecting unit. Light emitting devices (ITO/PEDOT/hyperbranched molecule/Ba/Al) have been fabricated.

Synthesis and properties of high efficiency light emitting hyperbranched conjugated polymers

A novel kind of hyperbranched conjugated light emitting polymers with 2,5-dimethyloxyl substituted phenylene vinylene as the connecting units and different hole or electron transporting groups such as dimethylaniline phenylene or pyridyl phenylene as the terminal groups were synthesized by modified one step Wittig polymerization reaction. The photophysical properties in solution and in films of hyperbranched conjugated polymers were studied in details. The oxidation potentials were measured by cyclic voltammetry. It was found that the hyperbranched conjugated polymers were highly soluble in common organic solvents, with good film-forming properties. In particular, the thermal stability of HPVs is extremely higher than that of linear polyphenylene vinylene derivatives. In addition, the LED, LEC devices using hyperbranched polymer as active layer were investigated. All results show that these novel hyperbranched conjugated polymers could be good candidates for the fabrication of high performance LED and other optoelectronic devices.

Photoinduced partial charge transfer between conjugated polymer and fullerene in solutions

Photoinduced charge transfer between a conjugated polymer and C60 and the related processes were investigated in dilute solutions. The substantial fluorescence quenching is correlated with the efficient exciton diffusion within the polymer chains, according to which a sphere-of-action mechanism is proposed. An emissive exciplex was found formed between the conjugated polymer and fullerene in a nonpolar solvent, indicating the occurrence of a photoinduced partial charge transfer process. The low-energy sites in the polymer are believed to play a crucial role in the partial charge transfer. The asymmetry of the exciplex provides a method for evaluating the tendency of photoinduced charge separation between the donor and the acceptor. This method allows screening candidates for photovoltaic applications.

Synthesis and Characterization of a Novel Hyperbranched Oligomer with 1,3,5-trisphenylbenzene as Cores

A novel hyperbranched oligomer with 1,3,5-trisphenyl benzene ring as cores and trisphenyl amino moieties as connecting groups was synthesized. It was characterized by FTIR, 1 H-NMR and 13 C-NMR, The intramolecular charge transfer phenomenon was found in its excited state, its emission color could be tuned by changing only the ratio of the mixed solvent.

β phase instability in poly(vinylidene fluoride/trifluoroethylene) thin films near β relaxation temperature

The β phase stability in poly(vinylidene fluoride/trifluoroethylene) [P(VDF-TrFE)] thin films was studied below 300 K using X-ray diffraction and polarization-electric-field (P-E) hysteresis loops measurements. On as-grown samples, an irreversible partial order-disorder transformation at Tβ ∼ 250 K, namely, the β relaxation temperature, was evidenced by the appearance of an additional X-Ray diffraction peak above Tβ as well as changes on the P-E loops on heating after the first cooling. This order-disorder-like transformation which is attributed to an all-trans order to helical disorder transition is suggested to take place in defect-rich regions like crystal-amorphous interphases and/or crystalline areas with randomly distributed TrFE defect-like units.

A Hyperbranched Dendritic Sensory Oligomer Based on Dibenzo-18-Crown-6 Receptors

A hyperbranched dendritic oligomer (CR-HPV) based on dibenzo-18-crown-6 as receptors was synthesized and characterized. The interaction of CR-HPV with metal ions in solution and film was studied by absorption, fluorescence spectra. LB films of CR-HPV with and without K + ions were fabricated and investigated by AFM and spectroscopy. The emission intensity was increased drastically as K + incorporated in CR-HPV both in solution and in LB film.

Photophysics and Applications in Plastic Solar Cells of Conjugated Polymer/Fullerene Composites

The photovoltaic applications of conjugated polymer/fullerene composites have attracted much attention from the scientific community. The photoinduced electron transfer and other related photophysical processes occurred in the composites are the central issues. Several kinds of conjugated polymers have been synthesized in our laboratory. Studies of their composites with fullerene are reviewed. We observed strong fluorescence quenching of these conjugated polymers on mixing them with C60 in dilute solution. Anion radical species of C60 were observed in ESR measurements as a result of photoinduced charge separation. The quenching constants vary with different conjugated polymers and thus provide a quantum measurement for the interaction between the donor and acceptor. Solar cells have been fabricated from these conjugated polymer/fullerene composites. Energy conversion efficiency up to 1.1% has been achieved.

Electroluminescent and photovoltaic properties of an alternating copolymer containing hole transporting moieties

An alternating copolymer with hole transport chromophores and arylene vinylenes, poly [triphenylamine-alt-2, 5-dimethoxy-1, 4-phenylene vinylene] (TPA-DMOPPV) was synthesized through Wittig reaction. The polymer has good solubility, thermal stability and excellent film-forming property. The photophysical properties of TPA-DMOPPV were investigated systematically. Light emitting diodes (LEDs) and photovoltaic cells (PVCs) with the polymer as active layers were fabricated and characterized. It was found that the polymer is promising for ap plication in LEDs and PVCs.