Noncovalent conformational locks in organic semiconductors

Highly planar conformation is considered to be one of the most important properties for high performance organic semiconductors. Among all kinds strategies for designing highly performing materials, noncovalent conformational locks(NCLs)have been widely used to increase the planarity and rigidity for π-conjugated systems. This review summarizes π-conjugated small molecules and polymers by employing various NCLs for controlling molecular conformation in the past two years. The optoelectronic properties of the conjugated materials, together with their applications on organic field-effect transistors(OFETs)and organic photovoltaics(OPVs) are discussed. Besides, the outlook and challenges in this field are also presented. It is obvious that NCLs play an important role in the design and synthesis of high-performance organic semiconductors.     

Bowl-shaped conjugated polycycles

The conjugated polycycles show excellent optical and electrical properties that are suitable for application in various organic electronics.While most of attentions have been paid to polycycles having planar π-conjugated system,the curved polycycles seem amazing due to their unique physical and chemical features.The non-planar conjugated polycycles have been created with the geometries of bracelet,saddle,bowl,Mobius band,helicenes,etc.Among them,the bowl-shaped one is of growing interest owing to the multidiscipline applications such as synthetic intermediates for end-cap of carbon nanotube,coordination with metal ions,encapsulation of fullerenes,and fabrication of electronic devices.In this paper,we summarize the recent advances on the chemistry of the bowl-shaped conjugated polycycles,particularly on their synthesis and the further chemical modifications toward organic functional materials.     

Second-order Nonlinear Optical Properties of a Series of Benzothiazole Derivatives

The second-order nonlinear optical (NLO) properties of a series of benzothiazole derivatives were studied by use of the ZINDO-SOS method.These chromophores are formed by a donor- π- bridge-acceptor system,based on a nitro group connected with benzothiazole as the acceptor and a hydroxyl-functional amino group as the donor.For the purpose of comparison,we also designed molecules in which nitrobenzene is an acceptor,The calculation results indicate that benzothiazole derivatives exhibit larger second-odrder polarizabilities than nitrobenzene derivatives.In order to clarify the origin of the NLO response of these chromophores,their electron properties were investigated as well.The benzothiazole derivatives are good candidates for application in electro-optical device due to their high optical nonlinearities,good thermal and photonic stability.     

Role of carbon matrix heteroatoms at synthesis of carbons for catalysis and energy applications

The conceptual ideas about the positive effects of N- and O-heteroatoms on the reactivity of carbons in gasification processes, their catalytic activity in electron transfer reactions, as well as the performance of the electrode double-layer supercapacitors due to their electron-donating influence on the π-conjugated system of graphene layers have been developed. This influence decreases both work function and band gap of carbons, and also significantly affects their electron-donating properties. As a result of our investigations based on quantum chemical calculations of model graphene clusters with N- and O-heteroatoms in different positions, prognostic data have been obtained. These data have been confirmed by our experimental results of catalytic activity of corresponding carbons in H2O2 decomposition reaction, their reactivity in gasification processes, and also their performance as electrodes in supercapacitors.     

Theoretical Study on One- and Two-Photon Absorption Properties of PPV Derivative with Electron-Donor Phenylanthracene as Pendent Group

Based on the equilibrium structures from quantum mechanics AM1 method, employing INDO/CI method and the sum-over-state （SOS） formula, the one-photon absorption （OPA） and two-photon absorption （TPA） properties as well as the second hyperpolarizabilities were discussed in detail for a kind of PPV derivative poly 2-（9-phenylanthracen-10-yl）-1,4-phenylenevinylene （P1）. The results indicate that the two-photon cross section （3） increases with the increasing of the number of repeating segment （n）, however only a slight increase corresponds to the increasing of molecular weight when the repeating unit number arrives at a certain number. From this point of view, the TPA cross section values of P1 were extrapolated through the linear fit of 3 value vs. 1/n. The δ value of P1 is as high as 181 GM （1 GM=10^-50 cm^4·s·photon^-1）. Concerning the influence of pendent group and extension of π-conjugation on 3 values, another four oligomers P2, PPV, P1-1, and P2-1 were investigated for comparison. The calculation results reveal that the position and property of pendent group have great influence on the OPA and TPA properties. A most crucial role for relatively larger 3 value was played by the extension of π-conjugation.     

Cooperative Supramolecular Polymerization of Propeller-Shaped Triphenylamine Cyanostilbenes for Explosive Detection

Self-assembly of π-conjugated compounds into supramolecular polymers has received considerable attention because of their intrinsic scientific interests and technological applications. As compared to π-conjugated rods, discotics, and macrocycles, propeller-shaped π-conjugated molecules have been less exploited to form long-range-ordered supramolecular polymers. Herein a novel type of supramolecular polymers has been constructed on the basis of propeller-shaped triphenylamine cyanostilbenes. The ...     

Triarylborane π-electron systems with intramolecular charge-transfer transitions

The incorporation of B element into π-conjugated system is an efficient strategy to tune the steric and electronic structure and thus optoelectronic properties of π-electron systems.The vacant p orbital on the tricoordinate B center makes it exhibit several electronic and steric features,such as electron-accepting ability through p-π~* conjugation,the high Lewis acidity to coordinate with Lewis bases,as well as the steric bulk arising from the aryl substituent on the B center to get enough kinetic stability.As a result,the boryl group is a very unique electron acceptor.When an electron-donating amino group is present,the triarylboranes would display intense intramolecular charge transfer transitions,which lead to interesting optoelectronic properties and great utilities.This short review summarizes the recent progress in π-electron systems,which contain both B and N elements and thus display intramolecular charge-transfer transitions.The triarylboranes are introduced based on their structural features,including the linear π-system with boryl and amino groups at the terminal positions,the lateral borylsubstituted π-system with amino groups at the terminal positions,the biphenyl π-system with an amino and a boryl groups at o,o'-positions,nonconjugated U- and V-shaped π-system,macrocylcic π-system with B and N embedded in the ring,B,N-bridged ladder-type π-system,as well as the polycyclicπ-system with B embedded in the center.     

两种吩噻嗪衍生物的合成，光学性质及其电化学性质

The synthesis, luminescence and electrochemical properties of two novel phenothiazine derivatives were presented, which exhibit good one-photon fluorescence emission. The quantum yields and solvent effects of them were studied in detail. Compound 3,7-bis（2-4＇-imidazolylbenzylidenehydrazonoethyl）-（0-ethylphenothiazine） （5） was used as an effective initiator, of which two-photon fluorescence spectra were investigated under 800 nm fs laser pulse and the measured two-photon absorption cross-section was 18 × 10^-50 cm^4·s per photon. Two-photon initiated polymerization microfabrication experiments were carried out. X-ray diffraction analyses revealed that the shape of the compound 3,7-bis（2-pyrid-4＇-ylmethylidenehydrazonoethyl）-（0-ethylphenothiazine） （4） looks like a butterfly with nearly planar wings. The dihedral angle of the two benzene rings is 37.6° and there is an obvious π-π stacking interaction between the molecules in the crystal.     

Enhancement of two-photon absorption cross section and singlet-oxygen generation in porphyrin-cored star polymers

We report a newly synthesized polymer of a star-shaped porphyrin compound(TPA-FxP) with four oligofluorene arms at its meso positions with the pronounced enhancement of the two-photon properties and the generation of singlet oxygen by utilizing the two-photon excited fluorescence resonance energy transfer.The steady-state spectra and transient triplet-triplet absorption spectra give evidence that the enhanced two-photon absorption cross section results from not only the through-space energy transfer(Frster...     

QM/MM Study of the Second Harmonic Generation and Two-photon Absorption Properties of a Fluorescent Proteins-Dreiklang

A new reversibly switchable fluorescent protein(RSFP), namely Dreiklang, exhibits prominent feature that the wavelengths for switching and fluorescence are decoupled due to its great different structures between bright and dark states. This feature might also induce some nonlinear optic(NLO) properties changing as switching between two states, which might promote new method of biological science. We employ the QM/MM method to simulate the structures of different states, and study their second harmonic generation(SHG) and two-photon absorption(TPA) properties. And we found different states of Dreiklang have different SHG and TPA responses. The SHG and TPA properties of Dreiklang are correlated to particularly geometrical structures of different states, especially the centrosymmetric or nocentrosymmetric π-stacking structures which are formed by chromophore and beside residue Tyr203, so the SHG and TPA responses could be changed as the light induces switching among different states of Dreiklang. This work would prospectively guide the application of Dreiklang on the NLO technology, and help the development of new RSFP with special NLO function.     

Two-photon spectroscopic behaviors and photodynamic effect on the BEL-7402 cancer cells of the new chlorophyll photosensitizer

The spectroscopic properties of a new chlorophyll derivate photosensitizer(CDP) are studied under the excitation wavelengths at 800 and 400 nm using femtosecond pulses from a Ti:sapphire laser.The damaging effect of CDP on the BEL-7402 cancer cells is also investigated upon two-photon illumination at 800 nm.The normalized fluorescence spectra of CDP in tetrahydrofuran(THF) show that two-photon and one-photon spectra have the same distributions and the same emission bands(675 nm).The life-times of two-and one-photon induced fluorescence of this molecule are of the order of 5.0 ns.By comparing the data it is shown that there is some difference between the two lifetimes,but the differ-ence is less than one nanosecond.The two-photon absorption cross section of the molecule is also measured at 800 nm and estimated as about σ′2 ≈ 31.5×10-50 cm4·s·photon-1.The results of two-photon photodynamic therapy(TPPDT) tests show that CDP can kill all of the tested cancer cells according to the usual Eosine assessment.Our results indicate that the two-photon-induced photophysical,photo-chemical and photosensitizing processes of CDP may be basically similar to those of one-photon ex-citation.These behaviors of the sample suggest that one may find other possible methods to estimate some photosensitizers' effects in details such as their distribution in cells and the reactive targets of the sub-cellular parts of some tumor cells via two-photon excitation techniques.     

Appended corrole manganese complexes:Catalysis and axial-ligand effect

A series of N-base appended corroles and their manganese complexes were synthesized and their binding constants with three different nitrogenous ligands, triethylamine, N-methylimidazole and pyridine, were evaluated by spectroscopy. Kinetic studies indicated that the presence of appended N- donor ligands may cause a significant enhancement of the rate of oxygen atom transfers （OAT） from （oxo）manganese（V） corrole to alkene, and the stronger axial ligand binding has impact on the rate of the oxidation reaction. Turnover frequency （TOF） for the catalytic oxidation of alkenes by appended manganese corroles varies with the following ligand order： acetamido 〈 pyridyl 〈 imidazolyl. The influence of the external axial ligands on the catalytic epoxidation was investigated by using appended acetamido manganese corrole as catalyst, with the results revealing that N-methylimidazole gave the best enhancement on the yields of total oxidation products among the investigated nitrogenous ligands.     

Colorimetric and electrochemical Pb~(2+) detection by imine-bridged tetrathiafulvalene-pyridine derivatives

Imine-bridged TTF-π-pyridine derivatives, 2NTTF, 3NTTF and 4NTTF, were synthesized and the cation-binding study was performed. It is noted that with the addition of the micromolar concentration of Pb2+ to the solution, these compounds display remarkable changes in solution color, 1H NMR spectra and electrochemical properties. The nitrogen atom of the imine-bridge in 2NTTF not only serves as a π-conjugated spacer but also participates in the sensing and coordinating properties.     

Synthesis, two-photon absorption and AIE properties of multibranched thiophene-based triphenylamine derivatives with triazine core

Two new multibranched thiophene-based triarylamine derivatives with 1,3,5-triazine core are synthesized and characterized. Their one-and two-photon absorption properties and aggregation-induced emission effect have been investigated. Both the STAPA-based compounds are AIE active. The two-photon absorption (2PA) cross sections measured by the open aperture Z-scan technique are determined to be 620 and 1610 GM for STAPA-a and STAPA-b in chloroform,respectively, which dramatically increase with the introduction of alkyl chains. The relationship between their structures and properties on one-and two-photon absorption and aggregation-induced emission is discussed, which allows us to examine the effect of introducing alkyl chains. In addition, solvent effects also show a significant influence on the 2PA cross section. The two compounds with excellent AIE and 2PA properties provide attractive alternatives for the biophotonic materials.     

Enhancement of Two-photon Absorption by Ce^3＋ Sensitization in Organic Dyes

The two-photon absorption(TPA)and TPA-induced frequency upconversion emission properties of the dyes 4-[P-(dicyanoethylamino)crystal]-N-methypyrdinium iodide and the complex of 4-[P-(dicyanoethylamino)crystal]-N-methypyrdinium iodide and Ce(NO3)3 were experimentally studied.It was found that the TPA cross section for the dye sensitized by Ce3 is two factors larger than that of the dye without being sensitized.A three-level system model of the dye molecules was used to analyze the enhancement of TPA by the sensitizer Ce3 ,which indicated that the sensitizer results in the increase of the transition dipole moment from the one-photon allowed excited state(1Bu)to the two-photon allowed excited state(2Ag).     

Synthesis,Characterization, and Linear and Nonlinear Optical Properties of Phenylene-vinylene Based Chromophores for Singlet Oxygen Generation

A series of symmetrical and unsymmetrical phenylene-vinylene （PV） based chro- mophores with the molecular configuration of donor-π-donor （D-g-D） were prepared and characterized. Iodine was first introduced into the Jr-conjugation backbone of the PV based chromophores in order to study the heavy atom effect on their linear absorption, two-photon absorption （TPA） properties, as well as singlet oxygen generation properties. TPA cross-sections of these chromophores were investigated by using the two-photon excited fluorescence method. The unsymmetrical chromophores were found to have larger TPA cross-section values compared to their symmetrical counterparts. For one of the unsymmetrical chromophores with the iodine incorporation, a large TPA cross section value with quenched emission was found. The decreased fluorescence quantum yield of a molecule can be ascribed to the increased intersystem crossing, which is favorable for enhancing the singlet oxygen generation. Therefore, the unsymmetrical PV based chromophores with heavy atom incorporation are promising singlet oxygen sensitizers for the photodynamic therapy application.     

Cationic conjugated polymers for detection and inactivation of pathogens

Conjugated polymers(CPs) are referred to a kind of fluorescent polymer materials with delocalized π-conjugated backbones.For the last decades, cationic CPs(CCPs) have been widely used in biosensor, imaging and biomedical fields due to their good photophysical properties and solubility in water medium resulting from side chain modification with ionized moieties. In this mini-review, we mainly introduced the applications of CCPs in detection and inactivation of pathogen with typical examples, and also briefly discussed the relevant mechanisms. We hold the expectation that this mini-review can offer researchers a general reference and inspire them to construct new systems with high performances of pathogen detection and antimicrobial activity.     

The First-principlies Calculations of the Electronic Structures and Optical properties of Ⅱ-Ⅲ2-Ⅵ4 （Ⅱ=Zn,Cd; Ⅲ= In; Ⅵ=Se,Te）

The electronic structures and optical properties of II-III2-VI4 （II = Zn, Cd; III = In; VI = Se, Te） compounds are studied by the density functional theory （DFT） using the Vienna ab initio simulation package （VASP）. Geometrical optimization of the unit cell is in good agreement with the experimental data. Our calculations show that the valence band maximum （VBM） and conduction band minimum （CBM） are located at G resulting in a direct energy gap. The optical properties are analyzed, and the independent second harmonic generation （SHG） coefficients are determined. By an analysis of the band structure, we can get that SHG response of the system can be attributed to the transitions from the bands near the top of valence band that are derived from the Se/Te p states to the unoccupied bands contributed by the p states of In atoms.     

A new D–D–π–A dye for efficient dye-sensitized solar cells

New metal-free organic dye sensitizers containing mono-triphenylamine or bis-triphenylamine as the electron donor, a thiophene as the π-conjugated system, and a cyanoacrylic acid moiety as the electron acceptor were synthesized. The optical and electrochemical properties of the dyes were investigated,and their performance as sensitizers in solar cells was evaluated. Dye-sensitized solar cells based on dye containing bis-triphenylamine as the electron donor produced a photon-to-current conversion efficiency of 6.06%(Jsc = 14.21 m A/cm~2, Voc = 0.62 V, ff = 0.69) under 100 m W/cm~2 simulated AM 1.5 G solar irradiation(100 m W/cm~2).