Junlin Yang

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.

Composites of C60 based poly(phenylene vinylene) dyad and conjugated polymer for polymer light-emitting devices

A C60-based poly(phenylene vinylene) (PPV) dyad poly{(2,5-di-pentoxyl-phenylene)-4diylvinylene-3,6-[9-(1-azafulleroid-propyl)-carbazolenevinylene]} (PPV–AFCAR) and an emissive conjugated polymer poly{1,4[2-(3,7-dimethyloctyloxy)-3,5,6-trimethoxy]phenylene vinylene} (POMPV) were prepared to investigate the role of [60]fullerene in conjugated polymer composites. Multilayer organic light-emitting devices with the configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/blends/2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(Bu-PBD)/LiF/Al were fabricated using PPV–AFCAR as a dopant and POMPV as an emissive material.

The new approaches to light emitting conjugated polymers - Alternating copolymers with hole transport chromophores and hyperbranched polymers

The alternating copolymers with hole transport chromophores and arylene vinylenes were designed and synthesized. A series of polyfunctional hyperbranched polymers with a dendrimer-like structure were also obtained. The photoluminescence properties have been studied. The luminescence efficiency and the processibility of the above polymers have been improved. It was found that these polymers are promising for light emitting materials.

Direct Evidence of Photoinduced Charge Transfer from Alternating Copolymer to Buckminsterfullerene

Fluorescence quenching of the alternating copolymer (TPA-PAV) obtained from triphenylamine dialdehyde and the 1,10-anthrylene di-ylide Wittig reagent has revealed exciplex formation by intramolecular charge transfer state of TPA-PAV and C60 in benzene solution. The formation of the exciplex may result in an irreversible photochemical reaction. The photoinduced charge transfer from TPA-PAV to C60 was investigated. Furthermore, ESR signals of the C60 anion radical were observed.

Photoinduced Intramolecular Charge Separation at the Repetition Units of Light‐Emitting Alternating Copolymers

Light-emitting nitrogen-containing poly(phenylene vinylene) PPV-related copolymers are synthesized by the weel-known Wittig-Horner reaction. The alternating copolymers have hole-transporting moieties such as triphenylamine (TPA) and conjugated aromatic units such as 1,4-phenylene, 1,4- or 1,5-naphthylene and 9, 10-anthrylene. The dipole moments within the repetition units of the copolymers in the excited state are estimated by measuring the solvent effect on absorption and fluorescense emission spectra, indicating that charge separation is present. The dipole moment values are in agreement with the electron affinities of aceptors, i.e. aromatic units. The evidence can help to elucidate the phtophysical behavior, particularly the fluorescence quantum efficiencies.

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.

Synthesis and Characterization of a Water-soluble Hyperbranched Poly(p-phenylene vinylene) (WHPV)

A water-soluble hyperbranched poly(p-phenylene vinylene)(WHPV) was synthesized through Wittig reaction. The polymer bore a -SO 3 -group in each connecting module, which makes the polymer water-soluble. The fluorescence emission band of the resulting polymer is located around 460 nm. Molecular dynamics simulation shows that the branches of the WHPV may construct many cavities and the -SO 3 -groups are located around the cavity walls. The interaction between WHPV and CdS nanoparticles should be fairly strong and the composite of WHPV with CdS nanoparticles can be obtained.

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.

Carbazole-containing light-emitting polymers: Properties of excited states

A series of light-emitting conjugated polymers alternatively involving carbazole and bivinylene arylene moieties in the main chain were synthesized via Wittig-Horner type copolymerization. The photoinduced charge transfer process relating to these polymers was investigated by using the technique of fluorescence spectroscopy. The interaction between excited copolymers and C60 in benzene solution was studied. The fluorescence quenching can be well described by the “sphere-of-action” mechanism. It is believed that two basic steps are involved in the quenching process, i.e. the diffusion of excitation within the conjugated polymers and the dissociation of the exctions trapped by fullerene. The radius of the sphere-of-action can be related to the excitation diffusion length, which depends on the lifetime of the exciton. The dynamic fluorescence quenching of the copolymers by another quencher, 1,4-dicyanobenzene (DCB) was also surveyed. Copolymers with different chain conformations show different temperature effects in the dynamic quenching. A planar conformation is beneficial for the quenching via bimolecular collision.