Conjugated Wide-bandgap Polygridarenes: Synthesis,Characterizations And Blue-emitting Stability

Deep blue-emitting materials are significant to the commercialization of full-color OLEDs,but most of them suffer from poor spectral stability,low color purity and evident incompatibility between the high-efficient performance and accessible solution/printing processing.Wide-bandgap polyfluorene derivatives can be flexibly designed for above requirements,whereas the main-chains are unavoidably subjected to interchain aggregation,fluorenone defects and intra-chain bending/torsion.As a result,the intrinsic deep blue emission is transformed into the excitonic g-band behaviors.To circumvent such green emission,covalent ladderization,steric hind-rance/capping,and cross-linking copolymerization have been applied to deactivate the free radical reaction sites(9-position of fluorene moieties)and thus suppress the interchain lumine-scence/exciton/polaron annihilation.Even so,it is difficult to explore the fluorenyl deep-blue emitting polymers with high stability and excellent performance.Based on the four-element principles and multi-steric hindrance strategy,we have developed gridarene-based covalent nanotechnologies and nanopolymers that evidently constrain conformational transitions and main-chain relaxations for strengthening thermal and optical stabilities.On this basis,as the synergistically molecular attractor–repulsor theory(SMART)plays a key role in improving conformational planarization,the fluorescence quantum yield and carrier mobility,we introduced PODPF repeat units into the nanogrid backbones and then designed a novel conjugated polygridarene chain PG-DPF.The work enables to inherit an even amplify the gridarenes’advantages including wide-bandgap semiconductors,strong optical/thermal stability and multi-steric characteristics,and use this material as light the layer is expected to realize OLED without film thickness dependence.First,we performed Yamamoto polymerization of nano-monomer G-DPF,obtained from Friedel-Crafts gridization of U-shaped and I-shaped nanosynthons in 80%yields,to afford conjugated polygridarenes PGDPF with the number-average molecular weight M_n of 21785,the polydispersity of 1.43 and the average degree of polymerization of 8.Then,we examined the comprehensive stability of PG-DPF(versus other conjugated polyfluorenyl derivatives)via thermal annealing,humid placement,and ultra-violet radiation.We observed that PG-DPF has excellent thermal stability in which the generated g-band has the weakest intensity under the conditions of high temperature(260 ~oC)in 8 hours.Meanwhile,we also observed the stable blue emission(without excitonic g-band behaviors)and the maintained photoluminescence intensity under the humid environment(75%).In contrast,through ultra-violet radiation(the wavelength of 365 nm),the PG-DPF unexpectedly generated the strongest g-band emissions,which indicates the crippled emission stability.We deduced that the pore structures on the PG-DPF backbones presumably influence the microscopic dynamics of oxygen molecules in which their diffusional motions are resctricted into the nanogrid backbones.Thus,the optical reduction reaction pathway is enhanced under the ultra-violet radiation.Finally,we applied PG-DPF as the light-emitting material of PLED in which the film thickness has negligible effect on the luminous efficiency,brightness and spectral stabilities.We believe that this work provides essential guidance for the flexbile electronics including the molecular design,film processing and device preparations,as well as the model building blocks for optical catalyst.