Design,Synthesis And Photophysical Study Of Light Emitting Materials Based On Bodipy And B-N Coordination Chelates

Organic emitting materials are widely used in the fields of dye,laser,photo sensor,bio-imaging and organic electronic devices with characteristics such as:innumerable molecular structures,fasile design and synthesis,and easy control of emission spectra.Thus,it is very important for us to study the photophysical properties of organic emitting materials,and new materials are in crying needs.BODIPY?boron-dipyrromethene?are classic organic dyes,which show properties of intense absorption,narrow full width at half maximum of absorption and emission spectra and highly fluorescence efficiency in solution.However,solid emission of BODIPY dyes in solid state are always dramatically quenched.Two reasons are contributed to the quenched fluorescence,one is the intense?-?stacking,and another one is self-absorption.Thus,BODIPY dyes with efficient solid emission need us to discover.Replace the fluorine atoms of BODIPY with other substituents will alternate the conjugation and electron-withdrawing properties of the BODIPY core,and for sure change the packing modes in solid state.Therefore,we introduce phenyls and bisphenyl to the BODIPYcore to obtain three derivatives.When the substituents are flexible phenyls,electron-withdrawing ability of BODIPY core is weakened,and the BODIPY plane is seriously distorted,then we could observe decreased molar absorbance and fluorescence efficiency.When the substituents are biphenyl,the electron-withdawing ability,planarity of the BODIPY core,molar absorbance and fluorescence all are increased.Though packing modes of the derivatives are alternated,aggregation caused quenching are still existing,and we need further decoration.D-A molecules with triphenylamine?TPA?groups as electron donors usually exhibit efficient emission in solid state.Therefore,based on the three BODIPY cores,we introduce TPA groups to different positions of BODIPY respectively.When there are large steric hindrance between TPA and BODIPY core,electron transition between donor and acceptor is forbidden.However,we found that if the interaction between donor and acceptor is strong enough,it will induce the distortion of the excited states in polar solvents,as a result,the forbidden transition becomes partially allowed.Materials of this kind show duel emission in polar solvents,one is local excited emission and another is charge transfer emission.These two emission are different in energy and lifetimes,which shows a phenomenon against Kasha rules.Only when the acceptor of the D-A system exhibits strong electron-withdrawing ability,could we observe this special phenomenon.Crystal structrues and solid fluorescence show that the introduction of TPA is benefit for the solid emission of these materials,and the highest efficiency reaches above 30%.When torsion angles between donor and acceptor are flexible,TPA groups in these molecules will exhibit electron-donating properties as well as conjugation effect.Though theoretical simulation and photophysical research,we recognize that radiative transition process of these materials in solutions are determined by the combined effect of S₀?S₁ transition and S₀?S₂ transition,the dominating transition process depends on the electron-withdrawing ability of the acceptors and the polarity of the solvents.Strong electron acceptor leads the molecule to charge transfer state,weak acceptor result in local excited state.If the donor and acceptor match with each other,we could observe an extraordinary stable hybrid local charge transfer?HLCT?state.The material with HLCT state emit brilliantly in crystalline state?38%?,which is the top level of D-A materials based on BODIPY.On the basis of BODIPY research,a series of conjugated heterocyclic chelates with multi B-N coordination bonds are designed and synthesized by us.These chelates are easy to synthesize,and facile to be modified.These materials are special in molecular structures,there are at least nine nitrogen atoms,three boron atoms,three B-N covalent bonds,three B-N coordination bonds and up to seven six-member heterocycles.The multi B-N coordination bonds lead the chelate to extremely low lying HOMO/LUMO energy levels as well as large energy gaps?3 eV?.The addition of conjugated donors to the chelate is benefit for the emission enhancement.Although there are quite a lot flexible aromatic rings,the fluorescence efficiency of the chelates can reach as high as 47%in solution and 32%in solid state,which is exceptionally anomalous.The convenient synthesis and abnormal photophysical properties make the brand-new chelates with high value in research and application.