| The conjugated polymers have the advantages of lower cost,solution processing,excellent flexibility and simpler preparation procedure,which attract massive attention and have been widely used in organic-field effect transistors as the active layer.Conjugated polymers with high charge carrier mobility usually require high crystallinity.However,the high crystallinity in conjugated polymers often correlates with poor mechanical resilience,which is unsuitable for flexible devices.Therefore,to obtain conjugated polymers in low crystallinity while still possessing a high carrier mobility is crucial for constructing flexible transistors.In this study,a special connecting mode between the functional units is realized by introducing multiple vinyl into the repeated unit,and a series of D-A conjugated polymers with multi-vinyl linked system have been constructed.The configurational and conformational isomerization effect from the vinyl linkages are utilized to maintaining the low crystallinity for the polymers in the solid state,while the carrier mobility is still improved.Moreover,the molecular structure is adjusted by changing the substituting position of the side alkyl chain,introducing F atoms and developing the expanded conjugated acceptor core,to find method on modulating the crystallinity and semiconductor characteristic of the thin film,as well as understand the relationship between molecular structure and charge carrier mobility of conjugated polymer.The details as follow:(1)A D-A conjugated polymer PTBTV based on benzothiadiazole(BT)and dithiophene with multiple vinyl as linkers was synthesized and characterized,the LUMO and HOMO energies of the polymer were characterized as-3.60 e V and-5.39 e V.Theoretical calculation with DFT suggested an enhanced planarity of the oligomer backbone for PTBTV.Bottom contact bottom gate organic field effect transistor devices based on PTBTV were fabricated and examined in air.After annealing at 160 oC,the devices exhibited excellent p-type performance of?h=3.2 cm2 V-1s-1,Ion/off=106,VT=-7 V.Such is among the highest performances of the BT–oligothiophene based polymers.The GIXRD pattern and AFM image(annealed at 160?)revealed a relatively low crystallinity.The feasibility of multiple vinyl linkage system to construct conjugated polymers with low crystallinity and high mobility was partially verified by this example.(2)A D-A conjugated polymer PTSBTV was synthesized,in which the substitution position of alkyl chains are the altered from polymer PTBTV.The LUMO and HOMO energies of the polymer were estimated to be-3.63 e V and-5.33 e V.Bottom contact bottom gate organic field effect transistor devices based on PTSBTV were fabricated and examined in air.After annealing at 160 oC,the devices exhibited fine p-type performance of?h=0.62 cm2 V-1s-1,Ion/off=106,VT=-7 V.The GIXRD pattern of the annealing optimized film revealed higher crystallinity than PTBTV.However,PTSBTV showed relatively lower performance,which might due to the low molecular weight of PTSBTV.DFT calculation also showed that the backbone of the polymer has a comparatively larger fluctuation and a low degree of linearity,which might affect the intra-chain charge transportation.(3)A D-A conjugated polymer PTFBTV based on difluorobenzothiadiazole(DFBT)and dithiophene with multiple vinyl as linkers was synthesized and characterized.The LUMO and HOMO energies of the polymer were estimated to be-3.60 e V and-5.59 e V.Single crystals of the corresponding monomer DVFBT and DVBT of conjugated polymers PTFBTV and PTBTV were obtained to investigate the role of fluorine in molecular packing,which suggested that the short non-covalent contact between the fluorine and the proton in the neighboring vinyl forms the C–H...F hydrogen bond and strengthens the backbone co-planarity as well as the intermolecular?-?interactions.However,the F...F intermolecular contact might be also be one of the reasons for the“face on”orientation of PTFBTV in the solid state.The optimized organic field effect transistor devices based on PTFBTV exhibited excellent p-type performance of?h=2.0 cm2 V-1s-1,Ion/off=105,VT=-5 V,Which is among the highest performances of the DFBT–oligothiophene based polymers,though slightly lower than that of the corresponding non-fluorine PTBTV.The GIXRD pattern and AFM image also revealed a relatively low crystallinity,proving PTFBTV a fine material with low crystallinity and high mobility.(4)A conjugated polymer PTNTV based on naphthobishiadiazole(NT)and dithiophene with multiple vinyl as linkers was synthesized and characterized.The LUMO and HOMO energies of the polymer are-3.70 e V and-5.30 e V,of which the LUMO energy level is slightly lower than those of PTBTV and PTFBTV.Top contact bottom gate organic field effect transistor devices based on PTNTV were fabricated and examined in air.After annealing at 160 oC,the devices exhibited outstanding ambipolar performance of?h=1.0 cm2 V-1s-1,Ion/off=103,VT=30 V and?e=0.4 cm2 V-1s-1,Ion/off=104,VT=100 V.Similar to PTBTV,the results of GIWAXS and AFM also showed low crystallinity of the thin films.The low energy barrier between each the conformational isomer fragment was verified by DFT calculation,indicating that the configurational isomerization of the vinyl linkage still contributes to the low crystallinity of PTNTV thin film.(5)A conjugated polymer PTFNTV based on difluoronaphthobishiadiazole(DFNT)and dithiophene with multiple vinyl as linker was synthesized.In summary,conjugated polymer materials with low crystallization and high mobility containing multiple vinyl linkage were successfully constructed.In this system containing thiadiazole units,the alternating of side alkyl chain position might influence the crystallinity largely;the introduction of F atom with the acceptor unit and the proton in the neighbouring vinyl forms the C–H...F hydrogen bond and strengthens the backbone co-planarity and intermolecular?-?interactions;the expansion of acceptor units is beneficial to form the inter-chain stacking between the conjugated polymer backbones,and reduce the band gap and LUMO level of the polymer,which is beneficial for the stability of the n-type properties.These results provide potential modification methods for further improve the properties of multi-vinyl link conjugated polymer system,which showed new molecular designing pathway on constructing organic semiconducting materials with low crystallization and high mobility. |
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