Hongzhen Lin

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.

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.

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.

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.

Spectroscopic characteristics of hyperbranched conjugated polymers studied by one- and two-photon excitations

Spectroscopic properties of new hyperbranched conjugated polymers functionalized in periphery with N,N-dimethylaniline and tert-butyl-benzene as terminal groups are investigated by one- and two-photon excitations. The absorption, fluorescence excitation and emission spectra are examined in chloroform and N,N-dimethylformamide. The two-photon excitation measurements show that the new hyperbranched conjugated polymer possesses large two-photon excitation cross section which makes it a very attractive candidate for the potential application as nonlinear optical materials. As an example, the two-photon induced three-dimensional data storage is also demonstrated.