Design And Applications Of Room Temperature Phosphorescence(RTP) Materials Based On Small Molecules Doped Polymers

Due to the exotic optical properties including long luminescence lifetimes,large stokes shifts,and high exciton utilization,organic room temperature phosphorescence(RTP)materials exhibit great superiority and prospect in applications of data encryption,environmental sensing,information storage,bioimaging and diagnostics,and colorful display,etc.,and become one of the hotspots in the field of organic optoelectronic materials.In general,the challenge to generate RTP for organic chromophores lies in the insufficient intersystem crossing(ISC)caused by weak spin-orbit coupling(SOC),ultrafast nonradiative decays,and oxygen quenching.A variety of strategies have been proposed to promote ISC processes by inclusion of heavy-and/or hetero-atoms and deuteration,and to suppress nonradiative relaxations by using crystal engineering,host-guest doping,crosslinking,polymerization,and many other methods.As the result,a surging number of organic RTP materials with long-lived lifetimes and high quantum yields under ambient conditions have been reported during the recent years.However,to realize practical use of the organic RTP materials in the above-mentioned applications,all-round demands must be satisfied for the materials.That is,besides the key criteria for optical properties of an organic RTP material,the material should also be processable,scalable,stable,cost-affordable.On the other hand,the polymer-based RTP materials,which normally bear amorphous morphology,have attracted special attentions due to their features in large-scale production and accessible processability.Quite a few polymer-based RTP materials have been prepared by chemical modification of traditional polymers and doping of organic chromophores into the polymer matrices.However,to create all-round players with long-lived RTP lifetimes,high quantum yields,and acceptable capacities in producibility and processability,most of the polymer-based materials are still unsatisfactory.The contradiction is even severe for the fullcolor and tunable-color phosphorescent materials,because most of the reported RTP strategies can only earn a train of long-lived RTP materials with similar phosphorescent colors in the blue or green regions.Phosphorescence color tuning to longer wavelength via molecular structure modification is a hard task in most cases,making RTP polymers with multicolored and colortunable phosphorescence still rare.Herein,we introduce some effective strategies to boost ultralong lifetime,high quantum yield and color-tunable phosphorescence in polymer-based RTP materials by adjusting the molecular structures and aggregate states of the doped phosphorescent chromophores.The main innovations and advances are as follows:(1)By employment of a selected series of hetero-or heavy-atom free polycyclic aromatic hydrocarbons(PAHs)as dopants and PMMA or PC as polymeric matrices,a family of Polymer-PAHs RTP materials was constructed.The T1 energy levels of PAHs could be tuned effectively from blue to orange through increasement of the conjugation degree;and upon codoping with a fluorescent dye,the RTP wavelength further extended to 650 nm,realizing fullcolor afterglows.Due to the weak SOC of the pure hydrocarbon PAHs,a slow radiative ISC transition from T1 to S0 leads to the blue,green,orange and red RTP possessing long-lived phosphorescence with lifetimes of 5500 ms under ambient conditions,among the champion values ever reported for the polymer-based RTP materials.Most importantly,the PolymerPAHs could be produced through various ways(solution,fibers,films,and complex 3D architectures).Application as anti-counterfeiting ink,information storage films,and as oxygen sensors were demonstrated showing the wide potential of the Polymer-PAHs.This study provides a family of all-round players with long-lived RTP lifetimes,high brightness afterglow,color-tunability,high productivity and diverse applications,as well as environmental(aqueous)stability-which we believe will facilitate practical applications of the widely-studied RTP materials.(2)By adoption of a selected series of isophthalonitrile derivatives(INs)as dopants and PMMA as polymeric matrix,a family of excitation-&concentration-dependent color-tunable ultra-long RTP materials(PMMA-INs)were constructed.Photophysical analyzation and theoretical calculation indicate that the color-tunability arises from the different existing forms of INs in PMMA,wherein the isolated molecules in the low doping concentration and the multiple aggregate state in the high concentration correspond to different triplet energy-levels and result in blue or green phosphorescence,respectively.By variation of the excitation wavelength from 200 to 400 nm,different doping content PMMA-INs exhibited distinct colortunable RTP response with a ultralong lifetime(up to 1077 ms).By using PMMA-4AIN with different doping concentrations to print different parts of encrypted patterns,multi-level encryption upon different UV source irradiation was demonstrated.The color-tunable and ultralong RTP plus the low-cost and nice processability,these features may provide PMMA-INs with more chances in high-level anticounterfeiting and security applications.(3)By adoption of 4-Methoxybenzonitrile(4MOBN)as dopants and PMMA as polymeric matrix,a RTP material(PMMA-4MOBN)with high quantum yield was constructed.PMMA4MOBN not only processed long phosphorescence lifetime(～580 ms),but also obtained the ultra-high phosphorescence efficiency(up to 56.08%).