Biaryl Derivatives With Amorphous Room-Temperature Phosphorescence/Solvent-Driven Sign Inversion Of Circularly Polarized Luminescence

The emissive small organic molecules are one important class of emissive materials owing to their significant advantages,such as light weight,facile structure modification and easy processing.The room temperature phosphorescence in the amorphous state and the circularly polarized luminescence switching under the external stimuli are two interesting but challenging properties for the emissive small organic molecules.The research in this thesis mainly focuses on these two topics.(1)Room-temperature phosphorescence(RTP)has attracted remarkable research interest due to its unique properties,such as long lifetime,the involvement of triplet states,and oxygen sensitivity,which have been applied in the fields of organic light-emitting diodes(OLEDs),chemical sensors,bioimaging,and anti counterfeiting technology.Although it has become possible to achieve RTP for small organic molecules through incorporation of heavy atoms,heteroatoms(e.g.,B,O,N,S),or carbonyls to promote the intersystem crossing(ISC)or through crystal formation,embedding into rigid host matrix,assistance of polymerization,and metal-organic framework(MOF)coordination to retard the molecular motion and thus to suppress the nonradiative decay pathways.However,the difficulties in the special processing have greatly impeded their practical utility.Ideally,the pure organic molecules could show RTP with high efficiency in the amorphous state without any special treatments.In this research,we found that a triarylborane-based biphenyl,4,4'-dibromo-2-dimesitylboryl-2'-(N,N-dimethylamino)biphenyl(Br2-BN-BPh)shows efficient RTP in the amorphous state.The phosphorescence quantum yields of vigorously ground powder and drop-cast film are 0.36 and 0.22,respectively.Owing to the presence of two bulky substituents at the lateral positions,the existence of the intramolecular ?-? interaction and the B…N electronic interaction,this compound is intramolecularly rigid,which is helpful to retard the vibrational motions and thus suppress the nonradiative decay in the solid state.In addition,this compound has a very small ?ES-T owing to the well separation of HOMO and LUMO as a result of the significant twisting of the biphenyl skeleton.The small ?ES-T together with the heavy atom eff ect of the bromo substituent is expected to increase ISC.Thus,both the steric and electronic effects of the dimesitylboryl group are important for the efficient RTP property of Br2-BN-BPh,especially in the amorphous state.This is the first example of RTP from meta-free organic triarylboranes.The current results would definitely lay the groundwork for the further rational design of metal-free organic molecules with improved RTP property.(2)The circularly polarized luminescence-active small organic molecules(CPL-SOMs)have recently attracted rapidly increasing interest owing to the broad application of CPL in 3D,information storage and processing,CPL laser,biological probes and signatures.At the same time,the CPL switching,which can be triggered by the external stimuli is becoming an important topic.Previously,our group has a triarylborane-based a class of binaphthyl derivatives with triarylborane,2,2'-bis(diphenlyamino)-6,6'-bis(dimesitylboryl)1,1'-binapthyl(BNPh2-BNaph),which shows intense CPL with both high quantum yield and high luminescence dissymmetry factor(glum).In addition,the CPL sign of this compound is inverted from cyclohexane to acetonitrile.In this research,we designed and synthesized 2,2'-bis(diphenlyamino)-6-dimesitylboryl-1,1'-binapthyl(MBNPh2-BNaph)to explore the influence of the unique structure consisting of two donor(D)-design-?-acceptor(A)subunits on the CPL properties.In addition,we also designed and synthesized other electron-acceptor-substituted 1,1'-binaphthyls,which are also characteristic of the composition of two D-?-A subunits with Mes2B replaced by other electron acceptors,such as formyl(CHO)(CHONPh2-BNaph),cyano(CN)(CNNPh2-BNaph),and 4-pyridy(PyNPh2-BNaph).It was found MBNPh2-BNaph shows much smaller glum although its CPL sign is also inverted from cyclohexane to acetonitrile,suggesting the importance of the structure consisting of two D-?-A subunits to achieve intense CPL.For other binaphthyl derivatives CHONPh2-BNaph,CNNPh2-BNaph,PyNPh2-BNap,which also consist of two D-?-A subunits,display similar CPL properties with BNPh2-BNaph,such as high quantum yield,high glum and solvent-driven CPL sign inversion,suggesting the general utility of the current molecular design for the solvent-driven CPL sign inversion.The obtained results in this research are expected to provide important basis for the design of CPL-SOMs with high quantum yield,high glum and switchable CPL under external stimuli.In the addition,the current results are also important for the practical applications of CPL-SOMs in 3D display,spintronics-based devices,biological probes and signatures.