Qingguo He

Improving the efficiency of solution processable organic photovoltaic devices by a star-shaped molecular geometry

A new solution processable star-shaped organic molecule S(TPA-BT) has been synthesized for application in organic solar cells (OSCs). The properties and structures of S(TPA-BT) and a related linear molecule L(TPA-BT) were studied, including UV-visible spectroscopy, hole charge mobility, and theoretical calculated geometry and electronic properties. S(TPA-BT) film shows a broader and stronger absorption band in the range of 440–670 nm, lower band gap of 1.86 eV, higher hole mobility of 4.71 × 10−5 cm2V−1 s−1 and better film-forming properties compared with those of L(TPA-BT) film. ITO/PEDOT:PSS/S(TPA-BT) or L(TPA-BT):PCBM/Ba/Al bulk-heterojunction OSCs were fabricated with S(TPA-BT) or L(TPA-BT) as donor material. The power conversion efficiency (PCE) of an OSC based on a blend of S(TPA-BT) and PCBM (1 : 3, w/w) reached 1.33% under A.M. 1.5 illumination, 100 mW cm−2, with a short-circuit current density (JSC) of 4.18 mA cm−2, an open circuit voltage of 0.81 V, and a fill factor of 39%. The PCE of 1.33% and Jsc of 4.18 mA cm−2 are among the highest values reported so far for solution processable OSCs.

High performance aniline vapor detection based on multi-branched fluorescent triphenylamine-benzothiadiazole derivatives: branch effect and aggregation control of the sensing performance

A series of benzothiadiazole-pyridine branched triphenylamine derivatives TPA1BP, TPA2BP and TPA3BP have been designed and synthesized to sense aniline vapor with distinguished sensitivity, selectivity and repeatability via photoinduced electron transfer (PET). Suitable energy levels ensure the high selectivity to aniline for all three sensory materials. However, the aggregations of the three materials in the film state on a quartz substrate increase along with the branches, which highly deteriorate the sensing performance for less efficient fluorescence, lower contact area and inferior vapor penetration. The oriented ZnO nanorod array is introduced as the substrate to eliminate the aggregation and enhance the sensing performance, because of its high surface-to-volume ratio and 3D structure. Therefore, the cooperative effect that the sensing performance of TPAnBP increases with the number of branches could be observed; fluorescence intensities of the films on the nano-substrate are 34%, 45% and 54% quenched for TPA1BP, TPA2BP and TPA3BP, respectively, after exposure to 300 ppm aniline vapor for less than 5 s. Moreover, the fluorescences of all three sensory materials are almost 100% recovered by eluting with fresh air for 20 s and could be reused immediately. The detection limits are predicted to be 1 ppm for TPA1BP, 100 ppb for TPA2BP and 1 ppb for TPA3BP according to the fitted plot, demonstrating a significant cooperative effect of the molecular branches.

Localized Emitting State and Energy Transfer Properties of Quadrupolar Chromophores and (Multi)Branched Derivatives

In order to better understand the nature of intramolecular charge and energy transfer in multibranched molecules, we have synthesized and studied the photophysical properties of a monomer quadrupolar chromophore with donor-acceptor-donor (D-A-D) electronic push-pull structure, together with its V-shaped dimer and star-shaped trimers. The comparison of steady-state absorption spectra and fluorescence excitation anisotropy spectra of these chromophores show evidence of weak interaction (such as charge and energy transfer) among the branches. Moreover, similar fluorescence and solvation behavior of monomer and branched chromophores (dimer and trimer) implies that the interaction among the branches is not strong enough to make a significant distinction between these molecules, due to the weak interaction and intrinsic structural disorder in branched molecules. Furthermore, the interaction between the branches can be enhanced by inserting π bridge spacers (-C═C- or -C≡C-) between the core donor and the acceptor. This improvement leads to a remarkable enhancement of two-photon cross-sections, indicating that the interbranch interaction results in the amplification of transition dipole moments between ground states and excited states. The interpretations of the observed photophysical properties are further supported by theoretical investigation, which reveal that the changes of the transition dipole moments of the branched quadrupolar chromophores play a critical role in observed the two-photon absorption (2PA) cross-section for an intramolecular charge transfer (ICT) state interaction in the multibranched quadrupolar chromophores.

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.

Design, synthesis and photophysical properties of a hyperbranched conjugated polymer

Abstract The conjugated dendrimer, poly(3,5-bisvinylic)benzene (HS1), was synthesized by two routes. Elementary analysis, FTIR, NMR and GPC spectra were used to characterize the dendrimer. HS1 has good solubility in common organic solvents although it does not contain long alkyl side chain. The photophysical properties in solution and net solid film are inspected. Absorption maxima were determined at 290 and 310 nm with a molar absorption coefficient in the order of 104, and the emission maxima were at 359 and 369 nm. The excitation spectrum is similar to that of the absorption. A mirror image relationship existed between the absorption and emission spectra characteristic of the rigid structure of the polymer. The Stokes shift (70 nm) is large, which means the large difference in the energy level between the ground and singlet excited state. The fluorescence quantum yield is about 36%. The net film of HS1 has a broad emission at 446 nm. The marked difference between the solution and net solid film in photophysical properties suggested the large change in intermolecular interaction from solution to the solid film state. Molecular mechanical calculations are used to aid the design and simulation of the structure of HS1. In generation 1–2, the optimized geometry shows a relatively good planarity. While the torsion appeared at the interference of the branches in generation 3 and the optimized geometry feels a zeolite structure. The calculation result is used to explain the experimental observation. The good photophysical properties and processing ability could make HS1 an ideal candidate in electroluminecence device as a blue emitter.

Two luminescent metal–organic frameworks with multifunctional properties for nitroaromatic compounds sensing and photocatalysis

Two new luminescent metal–organic frameworks (MOFs), [Zn(L)0.5(1,10-phen)(H2O)]·2H2O (1) and [Cd(L)0.5(1,10-phen)(H2O)]·2H2O (2), have been successfully synthesized using bis-(3,5-dicarboxyphenyl)terephthalamide(H4L) as organic linkers and 1,10-phen as auxiliary ligand under solvothermal conditions. The two complexes are isostructural and they both have 1D ladder chain structures. For the two complexes, the participation of the fluorescent ligand H4L not only gives rise to a strong photoluminescence emission as expected, but more interestingly, that ligand originated characteristic band could be quenched selectively by nitroaniline with a low detection limit. The results show that 1 and 2 can be promising fluorescence sensors for selective detecting and recognizing nitroaromatic compounds via fluorescence quenching mechanism. Meanwhile, the photocatalytic activities were also determined by UV light induced photodegradation of Rhodamine B (RhB) experiments. The obtained results indicate that 1 and 2 can be stable and good UV light driving heterogeneous photocatalyst, which can be used to treat effectively wastewater of organic dyes in the future.

Conjugated polymer-titania nanoparticle hybrid films: random lasing action and ultrasensitive detection of explosive vapors.

We have first demonstrated that a random laser action generated by a hybrid film composed of a semiconducting organic polymer (SOP) and TiO(2) nanoparticles can be used to detect 2,4,6-trinitrotoluene (TNT) vapors. The hybrid film was fabricated by spin-casting SOP solution dispersed with nanosized TiO(2) particles on quartz glass. The SOP in the hybrid film functioned as both the gain medium and the sensory transducer. A random lasing action was observed with a certain pump power when the size (diameter of 50 nm) and concentration (8.9 x 10(12)/cm(3)) of TiO(2) nanoparticles were optimized. Measurements of fluorescence quenching behavior of the hybrid film in TNT vapor atmosphere (10 ppb) showed that attenuated lasing in optically pumped hybrid film displayed a sensitivity to vapors of explosives more than 20 times higher than was observed from spontaneous emission. This phenomenon has been explained with the four-level laser model. Since the sensory transducer used in the hybrid polymer/nanoparticles system could be replaced by other functional materials, the concept developed could be extended to more general domains of chemical or environment detection.

Sensitivity gains in chemosensing by optical and structural modulation of ordered assembly arrays of ZnO nanorods.

Nanomaterials and -structures have attracted much attention owing to their applications to ultrasensitive nanodevices. In this work, ordered assembly arrays of ZnO nanorods have been hydrothermally fabricated and used as optical substrates of fluorescence sensors for toxic vapors. The unique fastigiate nanorod assembly combines merits of single fibers and clusters, possessing identical orientation, large surface-to-volume ratio, evanescent transmission, and evanescent coupling. As coated on the assembly arrays, different sensing materials all generated amplified spontaneous emission (ASE) action such that the fluorescence intensity of the narrowed spectrum was 52.4-fold enhanced. Results of sensing experiments indicate that sensors based on the assembly arrays displayed 100% elevated normalized quenching rate and several times longer full-load time compared with reference sensors. This work provides a facile method to fabricate secondary structures of 1D rigid material and presents a new way to design highly sensitive optic sensors. Furthermore, evanescent excitation caused ASE action of fluorescent organics, and the correlative sensitivity gain is of interest in both theoretical research and the applications field.

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.

Concise and Efficient Fluorescent Probe via an Intromolecular Charge Transfer for the Chemical Warfare Agent Mimic Diethylchlorophosphate Vapor Detection

Sarin, used as chemical warfare agents (CWAs) for terrorist attacks, can induce a number of virulent effects. Therefore, countermeasures which could realize robust and convenient detection of sarin are in exigent need. A concise charge-transfer colorimetric and fluorescent probe (4-(6-(tert-butyl)pyridine-2-yl)-N,N-diphenylaniline, TBPY-TPA) that could be capable of real-time and on-site monitoring of DCP vapor was reported in this contribution. Upon contact with DCP, the emission band red-shifted from 410 to 522 nm upon exposure to DCP vapor. And the quenching rate of TBPY-TPA reached up to 98% within 25 s. Chemical substances such as acetic acid (HAc), dimethyl methylphosphonate (DMMP), pinacolyl methylphosphonate (PAMP), and triethyl phosphate (TEP) do not interfere with the detection. A detection limit for DCP down to 2.6 ppb level is remarkably achieved which is below the Immediately Dangerous to Life or Health concentration. NMR data suggested that a transformation of the pyridine group into pyridinium salt via a cascade reaction is responsible for the sensing process which induced the dramatic fluorescent red shift. All of these data suggest TBPY-TPA is a promising fluorescent sensor for a rapid, simple, and low-cost method for DCP detection, which could be easy to prepare as a portable chemosensor kit for its practical application in real-time and on-site monitoring.