Unveiling the Effects of Interchain Hydrogen Bonds on Solution Gelation and Mechanical Properties of Diarylfluorene-Based Semiconductor Polymers

The intrinsically rigid and limited strain of most conjugated polymers has encouraged us to optimize the extensible properties of conjugated polymers.Herein,learning from the hydrogen bonds in glucose,which were facilitated to the toughness enhancement of cellulose,we introduced interchain hydrogen bonds to polydiarylfluorene by amide-containing side chains.Through tuning the copolymerization ratio,we systematically investigated their influence on the hierarchical condensed structures,rheology behavior,tensile performances,and optoelectronic properties of conjugated polymers.Compared to the reference copolymers with a low ratio of amide units,copolymers with 30%and 40%amide units present a feature of the shearthinning process that resembled the non-Newtonian fluid,which was enabled by the interchain dynamic hydrogen bonds.Besides,we developed a practical and universal method for measuring the intrinsic mechanical properties of conjugated polymers.We demonstrated the significant impact of hydrogen bonds in solution gelation,material crystallization,and thin film stretchability.Impressively,the breaking elongation for P4 was even up to~30%,which confirmed the partially enhanced film ductility and toughness due to the increased amide groups.Furthermore,polymer light-emitting devices(PLEDs)based on these copolymers presented comparable performances and stable electroluminescence(EL).Thin films of these copolymers also exhibited random laser emission with the threshold as low as 0.52μJ/cm^(2),suggesting the wide prospective application in the field of flexible optoelectronic devices.

Enhancement of morphological and emission stability of deep-blue small molecular emitter via a universal side-chain coupling strategy for optoelectronic device

Film morphology of emissive layers is crucial to the performance and stability of solution-processable organic light-emitting diodes(OLEDs). Compared to the interpenetration of conjugated polymer chain,small molecular emitter with a flexible side chain always presents easily aggregation upon external treatment, and caused π-electronic coupling, which is undesirable for the efficiency and stability of deep-blue OLEDs. Herein, we proposed a side-chain coupling strategy to enhance the film morphological an emission stability of solution-processable small molecular deep-blue emitter. In contrary to “parent” MC8 TPA,the crosslinkable styryl and vinyl units were introduced as ended unit at the side-chain of Cm TPA and OEYTPA. Interestingly, Cm TPA and OEYTPA films present a relatively stable morphology and uniform deep-blue emission after thermal annealing(160 ℃) in the atmosphere, different to the discontinuous MC8 TPA annealed film. Besides, compared to the Cm TPA and OEYTPA ones, serious polaron formation in the MC8 TPA annealed film also negative to the deep-blue emission, according to transient absorption analysis. Therefore, both Cm TPA and OEYTPA annealed film obtained at 140 ℃ present an excellent deep-blue ASE behavior with a 445 nm, but absence for MC8 TPA ones, associated with the disruption of annealed films. Finally, enhancement of device performance based on Cm TPA and OEYTPA film(~40%)after thermal annealing with a similar performance curves also confirmed the assumption above. Therefore, these results also supported the effectiveness of our side-chain coupling strategy for optoelectronic applications.

Fluorene pendant-functionalization of poly(N-vinylcarbazole)as deep-blue fluorescent and host materials for polymer light-emitting diodes

π-Electron coupling of pendant conjugated segment inπ-stacked semiconducting polymers always causes the formation of defect trapped sites and further quenched high-band excitons,which is harmful to the performance and stability of deep-blue polymer light-emitting diodes(PLEDs).Herein,considerate of“defect”carbazole(Cz)electromers in poly(N-vinylcarbazole)(PVK),a series of fluorene units are introduced into pendant segments(PVCz-DMeF,PVCz-FMeNPh and PVCz-DFMeNPh)to suppress the strongπ-electron coupling of pendant Cz units and enhance radiative transition toward fabricating sable PLEDs.Compared to PVCz-FMeNPh and PVCz-DFMeNPh,PVCz-DMeF spin-coated films show a relatively efficient deep-blue emission,completely similar to its single pendant chromophore,confirmed an extremely weak charge-transfer and electron coupling between adjacent pendant segments.Therefore,PLEDs based on PVCz-DMeF present stable and deep-blue emission with a high color purity(0.17,0.08),associated with extremely weak defect emission at 600∼700nm(induced by carbazole electromers).Finally,PLEDs based on PVCz-DMeF/F8BT blended films(1:1)also present the high maximum luminance(Lmax)of 6261 cd/m2 and current efficiency(CE_(max))of 2.03 cd/A,confirmed slightly trapped sites formation.Therefore,precisely control the arrangement and packing model of pendant units inπ-stacked polymer is an essential prerequisite for building efficient and stable emitter for optoelectronic devices.

Photoexcitation dynamics and energy engineering in supramolecular doping of organic conjugated molecules

Doping and blending strategies are crucial means to precisely control the excited states and energy level in conjugated molecular systems.However,effective models and platforms are rarely proposed to systematically explore the effects of the formation of trapped doped centers on heterogeneous structures,energy level and ultrafast photophysical process.Herein,for deeply understanding the impact of molecular doping in film energy levels and photoexcitation dynamics,we set a supramolecular N-B coordination composed by the conjugated molecules of pyridine functionalized diarylfluorene(host material),named as ODPF-Phpy and ODPF-(Phpy)2,and the molecule of tris(perfluorophenyl)borane(BCF)(guest material).The generation of the molecular-level coordination bond increased the binding energy of N atoms and tuned the band-gap,leading to a new fluorescent emission center with longer excitation wavelength and emission wavelength.The intermolecular Forster resonance energy transfer(FRET)in blending flms make it present inconsistent fluorescent behaviors compared to that in solution.The charge transfer(CT)state of N-B coordinated compounds and the changed dielectric constant of blending films resulted in a large PL spectra red-shift with the increased dopant ratio,causing a wide-tunable fluorescent color.The excited state behaviors of two compounds in blending system was further investigated by the transient absorption(TA)spectroscopy.Finally,we found supramolecular coordination blending can effectively improve the films'photoluminescence quantum yield(PLQY)and conductivity.We believe this exploration in the internal coordination mechanisms would deepen the insights about doped semiconductors and is helpful in developing novel high-efficient fluorescent systems.

Alkyl-chain branched effect on the aggregation and photophysical behavior of polydiarylfluorenes toward stable deep-blue electroluminescence and efficient amplified spontaneous emission

The control of the condensed superstructure of light-emitting conjugated polymers(LCPs)is a crucial factor to obtain high performance and stable organic optoelectronic devices.Side-chain engineering strategy is an effective platform to tune inter chain aggregation and photophysical behaviour of LCPs.Herein,we systematically investigated the alkyl-chain branched effecton the conformational transition and photophysical behaviour of polydiarylfluorenes toward efficient blue optoelectronic devices.The branched side chain will improve materials solubility to inhibit interchain aggregation in solution according to DLS and optical analysis,which is useful to obtain high quality film.Therefore,our branched PEODPF,POYDPF pristine film present high luminance efficiency of 36.1%and 39.6%,enhanced about 20%relative to that of PODPF.Compared to the liner-type sides'chain,these branched chains also suppress chain planarization and improve film morphological stability effectively.Interestingly,the branched polymer also had excellent stable amplified spontaneous emission(ASE)behaviour with low threshold(4.72μJ/cm2)and a center peak of 465 nm,even thermal annealing at 220℃in the air atmosphere.Therefore,side-chain branched strategy for LCPs is an effective means to control interchain aggregation,film morphology and photophysical property of LCPs.

本征可拉伸共轭聚合物在柔性光电子器件中的应用

Conjugated Polymers(CPs)have been extensively explored in academia and industry since the discovery of conducting polymers in 1977[1],owing to their solution processability,structural tunability,and potential applications in a wide variety of optoelectronic devices,such as organic light-emitting diodes(OLED),organic photovoltatics(OPV)and organic field-effect transistors(OFET).

Intrinsically Viscoelastic Supramolecular Conjugated Polymer toward Suppressing Coffee-Ring Effect

The rational molecular design of light-emitting conjugated polymers that inherently suppress the ubiquitous coffee-ring effect(CRE)is a great challenge and the critical bottleneck for printing displays.Herein,we describe a supramolecular route to construct an intrinsically viscoelastic rigid conjugated polymer(RCP)(PHDPF-Cz)toward avoiding the CRE without sacrificing optoelectronic properties.Theπ-πstacking interactions derived fromthe pendant carbazole(Cz)units enable PHDPF-Cz to self-assemble into criss-cross nanofibers and endow its solutionwith great viscosity.Consequently,a high-quality and continuous PHDPFCz film was obtained by impeding the transport of aggregates to the droplet edge due to outward capillary flow during evaporation,in sharp contrast to the random aggregate migration and rapid precipitation generated fromthe controlled poly[4-(6-(9H-diphenylaniline-9-yl)hexyloxy)-9,9-diphenylfluorene]-co-[5-(6-(9H-diphenylaniline-9-yl)hexyloxy)-9,9-diphenylfluorene]and poly(9,9-dioctylfluorene)solutions.Finally,an efficient random laser is also achieved based on these cross-linked films with ultrastable single-chain excitonic behavior,confirming the effectiveness of our design strategy.