Role of ball milling during Cs/X catalyst preparation and effects on catalytic performance in side-chain alkylation of toluene with methanol

Ball milling modification was performed on Cs/X catalysts before or after cesium ion exchange.Multiple characterization results(such as pyridine-FTIR,XPS,and solid-state NMR)demonstrated that ball milling played a distinct role in these two different preparation procedures of the catalyst.Ball milling performed after the cesium modification has a strong influence on the Cs/X structure and acid-base properties,which results in the enhancement of the catalytic performance for side-chain methylation of toluene with methanol.Detailed studies revealed that ball milling intensified the interactions between oxides and molecular sieves,which not only increased the dispersion of the Cs species but also generated some weaker basic centers.It is proposed that the new basic centers could be Si-O-Cs and Al-O-Cs,which are produced by breaking of the Si-O-Al bonds of the zeolite framework under the synergetic effect of ball milling and alkali treatment.These new active sites may help to promote the side-chain methylation reaction.However,excessive ball milling will lead to the vanishing of zeolite micropores,thus deactivating side-chain methylation activity,which indicates that microporosity plays a key role in side-chain methylation and individual basic centers cannot catalyze this reaction.

Enhancing the side-chain alkylation of toluene with methanol to styrene over the Cs-modified X zeolite by the assistance of basic picoline as a co-catalyst

Side-chain alkylation of toluene with methanol is a green pathway to realize the one-step production of styrene under mild conditions,but the low selectivity of styrene is difficult to be improved with by-products of ethylbenzene and xylene.In this study,a new way is introduced to improve the catalytic performance by means of assisting basic compounds as co-catalysts during the toluene side-chain alkylation with methanol to styrene.As a result,high activity of side-chain alkylation appears over the basic Cs-modified zeolite catalysts prepared by ion exchange and impregnation methods.This high performance should be mainly attributed to two co-catalysis actions:(1)the promotion of basic compounds for methanol dehydrogenation to formaldehyde as the intermediate for side-chain alkylation;(2)the suppression of the styrene transfer hydrogenation on basic Cs-modified zeolites to avoid the formation of ethylbenzene.Especially for Cs_(2)O/CsX-ex catalyst,the addition of 2%mol/mol 2-picoline in reaction mixture could achieve both 12.3%toluene conversion and 84.1%styrene selectivity.Whereas the higher concentration of 2-picoline(>6%mol/mol)caused an inhibition to the catalytic activity because the excessive basic compound poisoned the combined acid-base pathway required for the side-chain alkylation process.In addition,two possible side-chain alkylation reaction routes on Cs-modified zeolite under the different 2-picoline absorption were described.

Efficient small-molecule donor with improved structural order and molecular aggregation enabled by side-chain modification

Side-chain modification is a proven effective approach for morphology manipulation in organic solar cells(OSCs).However,in-depth analysis and investigation involving side-chain modification towards morphology improvement,including molecular microstructure,orientating packing and aggregation are urgent for all-small-molecule(ASM)systems.Herein,employing a fluorine-modified two-dimension benzodithiophene(BDT)as central unit,we contrastively synthesized two small-molecule donors,namely BDT-F-SR and BDT-F-R,each welding alkylthio side-chains on thienyl of central BDT unit and the other grafted non-sulfuric alkyl side-chains.As predicted,the synergetic side-chain modification of fluorination and alkyl changeover triggers diverse molecular dipole moments and orientations,resulting in different molecular energy levels,thermal stabilities,molecular planarity and order.Eventually,together with the preeminent small-molecule acceptor Y6,BDT-F-R-based ASM OSCs obtain enhanced power conversion efficiency(PCE)of 13.88%compared to BDT-F-SR-based devices(PCE of 12.75%)with more suitable phase-separation and balanced carrier mobilities.The contrast results reveal that alkyl sidechains seem to be a more satisfactory partner for fluorine-modified 2D BDT-based small-molecule donors compared to alkylthio pendants,and highlight the significance of subtle side-chain modification for molecular structural order fun-tuning and morphology control,laying the foundation for efficient ASM OSCs.

A Novel Diamine,4'-Phenyiphenyi 4-(3",5"-Diaminobenzoyioxy)-benzoate and Longer Side-chain Polyimide

This is a part of our systematic research work on polyimides with mesogenic unit side chain. In this study, a new 4＇-phenylpbenyl 4-（3＂,5＂-diaminobenzoyloxy）benzoate and polyimide were synthesized, and characterized by FTIR, ^1H-NMR, inherent viscosity, mechanical properties, and solubility measurements. The diamine composed with mesogenic unit aryl ester groups and bipbenyl group with longer L/D ratio, was synthesized by two key steps. Firstly, the hydroxy group of 4-hydroxybenzoic acid was protected by acetoxy group for avoiding self- polymerization of 4-hydroxybenzoic acid, and then selectively hydrolyzed after esterification of carboxyl. Secondly, a selective catalysis hydrogenation was adopted to prevent the aryl ester from deoxidation. Based on this diamine, a novel polyimide was prepared by polycondensation of 4＇-phenylphenyl 4-（3＂, 5＂-diaminobenzoyloxy）benzoate and 4-aminophenyl ether（ODA） with 4, 4＇-oxydiphthalic anhydride（ODPA） in N-methyl-2-pyrrolidone （NMP）. The resulting polyimide with longer side chain showed better solubility and more regular structure. Its inherent viscosity is lower than that without side chains, but its modulus and strength not only maintained, even improved.

MORPHOLOGICAL AND KINETIC STUDIES OF PHASE TRANSITIONS OF A SIDE-CHAIN LIQUID CRYSTALLINE POLYMER

The morphological changes of a side-chain liquid-crystalline polymethacrylate during isotropization and liquid-crystallization transitions were studied by means of polarizing microscopy. These transitions were found to be composed of the initiation of a new phase at local places of the old phase matrix and the growth of the new phase: domains. The kinetics of the liquid-crystallization of the polymer from an isotropic melt to a smectic mesophase was also investigated. The isothermal process of the transition can be described by the Avrami equation. The values of the Avrami exponent were found to be around 2.6. which is lower than the value usually obtained for crystallization transition of polymers, but larger than that reported for liquid-crystallization transition of main-chain polymers. These results may indicate the difference in growth geometry of new phase during transition between crystallization and liquid-crystallization in general and between liquid-crystallization of main-chain and side-chain polymers. It was found that the liquid-crystallization of the used side-chain polymethacrylate may occur at small undercoolings with high transformation rate similar to that of main-chain polymers and small-molecule liquid crystals, while the crystallization of polymers can only proceed at large undercoolings. These phenomena can be explained by the idea that the surface free energy of nucleus during liquid-crystallization transition is less than that for crystallization, and evidence was obtained from analysis of the temperature dependence of the transformation rate.

MECHANICAL PERTURBATION INDUCED MOLECULAR ALIGNMENTS IN A SIDE-CHAIN LIQUID CRYSTALLINE POLYACETYLENE, POLY{10-[4-(4'-METHOXYPHENOXY-CARBOML)PHENOXYCARBONYL]-1-DECYNE}

A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily 'tunab1e' by simple mechanical perturbation. Thepolymerization of 10- [ 4 - (4' -methoxyphenoxycarbonyl )phenoxycarbonyl] - 1 -decyne (4 ) in itiated by theWCl_6-Ph_4Sn/dioxane complex yields polymer 5 with a M_w of 28400. The molecular structure of 5 ischaracterized by NMR, IR, and UV spectroscopy and its liquid crystalline behavior is investigated by DSC,POM, and XRD analysis. Upon mechanical perturbation, 5 exhibits unusual agitation-induced high-strengthdisclinations, shear-induced inversion walls, and solidification-induced banded textures. Such phenomenahave been observed in the main-chain liquid crystalline polymers with rigid backbones, but have seldom beenreported for the side-chain liquid crystalline polymers with flexible backbones, suggesting that the rigidpolyacetylene backbone of 5 plays a constructive role in inducing the novel molecular alignments.

The effect of intermolecular interactions on photoluminescence of a porphyrin side-chain polymer

Photoluminescence properties and exciton decay dynamics in a porphyrin side-chain polymer, poly[porphyrin acrylate- acrylonitrile （abbreviated p[（por）A-AN]）, have been investigated by femtosecond time-resolved photoluminescence spectroscopy. All the luminescences of p[（por）A-AN] films are due to the emissive decay of the photoexcited singlet excitons in the porphyrins. The luminescence efficiencies and lifetimes are increased for samples from pure films to dilute blend films. However, they are increased as the intrachain concentration of the porphyrin sidechain groups is decreased. The intrachain rotation motions of porphyrin sidechain groups result in the initial ultrafast luminescence decays, which are much faster than those due to the interchain interactions. All the samples show no significant red-shift and broadening of the transient luminescence spectra. The interchain and intrachain nonradiative exciton relaxation processes may play an important role in the luminescence dynamics in the p[（por）A-AN] films. The possible origin of different intrachain and interchain dynamic behaviours in p[（por）A-AN] films is discussed.

MORPHOLOGICAL STUDIES OF A THERMOTROPIC SIDE-CHAIN LIQUID CRYSTALLINE POLYMER DURING MESOPHASE TRANSITIONS

The morphological features of a side-chain liquid crystalline polymer during the mesophase transitions were investigated by using the DSC technique. The polymer used was polyacrylate with mesogens of three benzene rings attached to the main chain through a flexible spacer. A special two-phase texture was observed in the transition temperature range. Similar to main-chain liquid crystalline polymers the transition process of the side-chain liquid crystalline polymer was composed of an initiation of the new phase at local places of the old phase matrix and a growth process of the new phase domains.

Methylthio side-chain modified quinoidal benzo-[1,2-b:4,5-b']dithiophene derivatives for high-performance ambipolar organic field-effect transistors

Quinoidal small molecule semiconductors hold huge potential in ambipolar organic field-effect transistors(OFETs)and organic spintronic devices.Here,two quinoidal molecules with methylthio side chains were synthesized to develop molecular semiconductors with high ambipolar mobility,designated QBDTS and QTBDTS.The theoretical calculation results reveal that QBDTS has a closed-shell structure while QTBDTS showed an open-shell structure with a biradical character(y0)of 0.46 and its magnetic properties were further investigated using electron paramagnetic resonance(EPR)and superconducting quantum interference device(SQUID)methods.The methyl side chains showed a large impact on the molecular orbital levels.The HOMO/LUMO levels of QBDTS and QTBDTS were measured to be-5.66/-4.56 and-5.27/-4.48 eV,respectively,which are favorable for ambipolar charge transport in OFETs.Importantly,the spin-coated QBDTS displayed hole and electron mobilities of 0.01 and 0.5 cm^(2)V^(-1)s^(-1)while QTBDTS showed a record high hole mobility of 1.8 cm^(2)V^(-1)s^(-1)and electron mobility of 0.3 cm^(2)V^(-1)s^(-1).Moreover,comparative studies of the thin film morphologies also manifested the beneficial influence of methyl side chains on film crystallinity and molecule orientation.These results strongly proved that methyl side chain engineering can be a simple but efficient strategy for modulating electronic properties and molecular stacking behaviors.This work also represents a big advancement for quinoidal molecular semiconductors in ambipolar OFET applications.

Side-Chain Engineering of Non-Fullerene Acceptors with Trialkylsilyloxy Groups for Enhanced Photovoltaic Performancet

Side-chain engineering has emerged as a highly effective strategy for tailoring the aggregation behavior and charge transport properties of non-fullerene small molecule acceptors(SMAs).In this study,we designed and synthesized two SMAs,namely BTPSi-Bu and BTPSi-Pr,respectively incorporating tributylsilyloxy and trisopropylsilyloxy groups in their outer positions.Notably,BTPSi-Bu exhibited better planarity,crystallization,and favorable phase separation when paired with PM6 donor polymer compared to its counterpart,BTPSi-Pr.The resulting organic solar cells,utilizing the PM6:BTPSi-Bu blend,demonstrated a remarkable power conversion efficiency of 17.41%and a high open-circuit voltage of 0.859 V.These findings underscore the significance of integrating trialkylsilyloxy side chains into SMAs as a rational design approach for enhancing the performance of photovoltaic systems.

Side-chain symmetry-breaking strategy on porphyrin donors enables high-efficiency binary all-small-molecule organic solar cells

Side-chain symmetry-breaking strategy plays an important role in developing photovoltaic materials for high-efficiency all-small-molecule organic solar cells(ASM OSCs).However,the power conversion efficiencies(PCEs)of ASM OSCs still lag behind their polymer-based counterparts,which can be attributed to the difficulties in achieving favorable morphology.Herein,two asymmetric porphyrin-based donors named DAPor-DPP and DDPor-DPP were synthesized,presenting stronger intermolecular interaction and closer molecular stacking compared to the symmetric ZnP-TEH.The DAPor-DPP:6TIC blend afforded a favorablemorphologywith nanoscale phase separation and more ordered molecular packing,thus achievingmore efficient charge transportation and suppressed charge recombination.Consequently,the DAPor-DPP:6TIC-based device exhibited superior photovoltaic parameters,yielding a champion PCE of 16.62%higher than that of the DDPor-DPP-based device(14.96%).To our knowledge,16.62%can be ranked as one of the highest PCE values among the binary ASM OSC filed.Thiswork provides a prospective approach to address the challenge ofASM OSCs in improving film morphology and further achieving high efficiency via side-chain symmetry-breaking strategy,exhibiting great potential in constructing efficient ASM OSCs.

Polymer donors with hydrophilic side-chains enabling efficient and thermally-stable polymer solar cells by non-halogenated solvent processing

Polymer solar cells(PSCs)with high power conversion efficiency(PCE)and environment-friendly fabrication are the main requirements enabling their production in industrial scale.While the use of non-halogenated solvent processing is inevitable for the PSC fabrication,it significantly reduces the processability of polymer donors(PDS)and small-molecule acceptors(SMAs).This often results in unoptimized blend morphology and limits the device performance.To address this issue,hydrophilic oligoethylene glycol(OEG)side-chains are introduced into a PD(2EG)to enhance the molecular compatibility between the PD and L8-BO SMA.The 2EG PD induces higher crystallinity and alleviates phase separation with the SMA compared to the reference PD(PM7)with hydrocarbon side-chains.Consequently,the 2EG-based PSCs exhibit a higher PCE(15.8%)than the PM7-based PSCs(PCE=14.4%)in the ortho-xylene based processing.Importantly,benefitted from the reduced phase separation and increased crystallinity of 2EG PDS,the 2EG-based PSCs show enhanced thermal stability(84%of initial PCE after 120 h heating)compared to that of the PM7-based PSCs(60%of initial PCE after 120 h heating).This study demonstrates the potential of OEG side-chain-incorporated materials in developing efficient,stable,and eco-friendly PSCs.

Chlorination strategy on polymer donors toward efficient solar conversions

Bulk heterojunction(BHJ)polymer solar cells(PSCs)are promising candidates for next-generation solar cells.Benefitting from the persistent efforts in material design and synthesis,systematic device engineering and fundamental understanding of the device physics,the power conversion efficiency(PCE)of single PSC has been pushed to surpass 15%,and that of the tandem PSCs is over 17%.Recently,chlorination has drawn much interest and the chlorinated PSCs have been frequently reported in donor-acceptor(D-A)type conjugated polymers.This review summarizes the recent progress of the chlorinated strategy for highly efficient photovoltaic applications.We firstly discuss the chlorination on the acceptor units in D-A type donor polymers,emphasizing the 4 widely used acceptor units with their improved PCE.secondly,the chlorination on the donor units will be discussed,mainly focusing on the chlorination of benzo[1,2-b:4,b]dithiophene(BDT)unit and 2,2-bithiophene unit.Remarkably,the PCE of the chlorinated BDT-based device has been improved to over 14%.Overall,this review discusses the structure-property correlations of these chlorinated polymers in photovoltaic study,which could further provide guidance on the chlorinated strategy and the molecular design for high-performance photovoltaic devices.

N-alkyl chain modification in dithienobenzotriazole unit enabled efficient polymer donor for high-performance non-fullerene solar cells

Molecular design of either polymer donors or acceptors is a promising strategy to tune the morphology of the active layer of organic solar cells,enabling a high-performance device.Thereinto,developing novel polymer donors is an alternative method to obtain high photovoltaic performance.Herein,we present a facile side-chain engineering on the dithiophenobenzotriazole(DTBTz)unit of newly-designed polymer donors(named p BDT-DTBTz-EH and p BDT-DTBTz-Me)to boost the performance of non-fullerene solar cells.Compared with p BDT-DTBTz-EH with long N-alkyl side chains,p BDT-DTBTz-Me with a short methyl exhibits stronger molecular aggregation,higher absorption coefficient,and preferred face-on orientation packing.As a consequence,p BDT-DTBTz-Me based devices achieve an optimal power conversion efficiency of 15.31%when donors are paired with the narrow bandgap acceptor Y6,which is superior to that of p BDT-DTBTz-EH based devices(9.17%).Additionally,the p BDT-DTBTz-Me based devices manifest more effective charge separation and transfer than p BDT-DTBTz-EH based devices.These results indicate that fine-tuning side chains of polymer donors provide new insights for the design of high-performance polymer donors in non-fullerene solar cells.

POLYMER SCAFFOLDS BEARING AZOBENZENE-POTENTIAL FOR OPTICAL INFORMATION STORAGE

The fundamental optical storage mechanism of the laser light eddressable azobenzene moiety is briefly introduced.A modular and flexible synthesis design furnishes polyester matrices covalently integrating cyanoazobenzene in regularlyspaced side chains. Thin films of these materials are particularly well suited for holographic storape. Notable figures of meritsof liquid crystalline polyesters are response time to blue-green laser light of the order of nanoseconds, storage capacityexpressed as 5000 lines/mm, and high, permanent (almost nine years) diffraction efficiency of the order of 50% or greater,and erasability, The implications of the main chain nature for polyester morphology and for the permanency of the inducedanisotropy are discussed, The design and methods of preparation of other significantly different polymer scaffolds supportingcyanoazobenzene are elaborated. Oligopeptides always result in amorphous materials, whereas copolymethacrylates anddendritic or hyperbranched polyesters provide some materials that exhibit liquid crystallinity. However, none of these scaffolds affords materials that result in permanent anisotropy when exposed to interfering laser light.

Gradually modulating the three parts of D-π-A type polymers for high-performance organic solar cells

Organic solar cells(OSCs)have received great attention for the prominent advantage of low-cost,light-weight and potential for fabricating flexible and semi-transparent device via roll-to-roll printing toward making better use of inexhaustible renewable clean energy during the past years[1-4].

Low-bandgap polymers with quinoid unit as π bridge for high-performance solar cells

To construct efficient low band gap polymers,increasing the Quinone structure of the polymer backbone could be one desirable strategy.In this work,two D–Q–A–Q polymers P1 and P2 were designed and synthesized with thiophenopyrrole diketone(TPD)and benzothiadiazole(BT)unit as the core and ester linked thieno[3,4-b]thiophene(TT)segment as π-bridging,and the main focus is to make a comparative analysis of different cores in the influence of the optical,electrochemical,photochemical and morphological properties.Compared with the reported PBDTTEH–TBTTHD-i,P1 exhibited the decreased HOMO energy level of-5.38 e V and lower bandgap of 1.48 e V.Furthermore,when replaced with BT core,P2 showed a red-shifted absorption profile of polymer but with up-shifted HOMO energy level.When fabricated the photovoltaic devices in conventional structure,just as expected,the introduction of ester substituent made an obvious increase of VOC from 0.63 to 0.74 V for P1.Besides,due to the deep HOMO energy level,higher hole mobility and excellent phase separation with PC71 BM,a superior photovoltaic performance(PCE=7.13%)was obtained with a short-circuit current density(JSC)of 14.9 m A/cm^2,significantly higher than that of P2(PCE=2.23%).Generally,this study highlights that the strategy of inserting quinoid moieties into D–A polymers could be optional in LBG-polymers design and presents the importance and comparison of potentially competent core groups.

Deformation of amorphous azobenzene-containing polymer films induced by polarized light

Photomechanical response of amorphous polymer films containing azobenzene chromophores in side chains is studied. By invoking the trans-cis isomerization mech- anism, the steady-state deformation of the film induced by uniform illumination of linearly polarized light is obtained analytically. The deformation turns out to be of entropic origin,produced to compensate the entropy decrease due to photo-induced redistribution of azobenzene chromophores normal to the polarization direction. The predicted elongation direction of the film is consistent with previous experimental observations.

Highly Fluorescent Semiconducting Two-Dimensional Conjugated Polymer Films Achieved by Side-Chain Engineering Showing Large Exciton Diffusion Length

Semiconducting two-dimensional conjugated polymers(2DCPs)with strong fluorescence emission have great potential for various optoelectronic applications.However,it is enormously challenging to achieve this goal due to the significant compact interlayerπ-πstacking-induced quenching effect in these systems.In this work,we found that highly fluorescent semiconducting 2DCPs can be prepared through an effective side-chain engineering approach in which interlayer spacers are introduced to reduce the fluorescence quenching effect.The obtained two truxene-based 2DCP films that,along with-C6H13 and-C_(12)H_(25)alkyl side chains as interlayer spacers both demonstrate superior fluorescence properties with a high photoluminescence quantum yield of 5.6%and 14.6%,respectively.These are among the highest values currently reported for 2DCP films.Moreover,an ultralong isotropic quasi-twodimensional exciton diffusion length constrained in the plane with its highest value approaching 110 nm was revealed by the transient photoluminescence microscopy technique,suggesting that theπ-conjugated structure in these truxene-based 2DCP films has effectively been extended.This work can enable a broad exploration of highly fluorescent semiconducting 2DCP films for more deeply fundamental properties and optoelectronic device applications.

Improvement of photovoltaic properties of benzo[1,2-b:4,5-b′]difuran-conjugated polymer by side-chain modification

The development of polymer solar cells(PSCs)for the donor materials based on benzo[1,2-b:4,5-b′]dithiophene(BDT)has significantly boosted the power conversion efficiency(PCE).However,the PCE of polymer donor materials for benzo[1,2-b:4,5-b′]difuran(BDF)-based lags far behind that of their BDT analogs.To further explore efficient copolymers based on BDF units,a two-dimensional(2D)side-chain strategy was proposed to investigate the atom-changing effects on the copolymer donors for the properties of electron and optical.In this study,we designed and synthesized three new BDF-based copolymer donor materials,named PBDF-C,PBDF-O,and PBDF-S.Owing to the balanced charge transport and favorable phase separation of PBDF-S:Y6,a high PCE of 13.4%,a short-circuit current(J sc)of 25.48 mA cm−2,an open-circuit voltage(V oc)of 0.721 V,and a fill factor(FF)of 72.6%was obtained.This research demonstrates that the BDF building block has great potential for constructing conjugated copolymer donors for high-performance PSCs and that 2D side-chain modification is a facile approach for designing high-performance BDF-based copolymer materials.