Study On The Luminescence Behavior And Mechanism Of Atypical Compounds Containing Nitrogen/oxygen Atoms

Luminescent materials,especially nonconventional luminophores,have attracted more and more attention due to their simple preparation and good hydrophilicity.Based on the earlier exploration of aggregation-induced emission(AIE)mechanism of conventional luminophores and clustering-triggered emission(CTE)mechanism,scientists generally believe that compounds with oxygen atom(O),nitrogen atom(N)and other heteroatoms,double bond(C=C),carbonyl groups(C=O)and other non conjugated groups can form a 3D space electron interaction channel.Since,visible light can be emitted by enhancing spin orbit coupling(SOC)and intersystem crossing(ISC).However,with the development of the research on this kind of luminescent compounds,maleic anhydride(MAH),as a molecule with both O atom and unsaturated subunit,was found that its pure crystal can't emit light at room temperature,but have dual emission of fluorescence and phosphorescence at low temperature,which promoted further study.From the aspect of vibrational rotation of the bond and conformational rigidity of molecules,the photophysical properties,including prompt and delayed spectrum,lifetime and ultraviolet absorption,and CTE mechanism of succinic anhydride(SA),maleimide(MA)and their dimers(BMA,BSU)made up of O/N atoms and C=O group were studied respectively.The quenching effect of bond vibration and insufficient rigid conformation on molecular luminescence can be further confirmed by single crystal X-ray diffraction,which explained the importance of effective inter/intra molecular force,3D electron interaction channel and rigidity of molecular conformation for fluorescence and phosphorescence emission.This study provides a new way to explain the reason of non luminescent behavior of some molecules and a new design concept for building luminescent molecules.Subsequently,in order to study the effect of through-space conjugation on phosphorescence emission,and design effective and persistent room temperature phosphorescence(p-RTP)compounds,two kinds of adducts of Diels-Alder reaction(D-A reaction)were synthesized based on MA,N-Methylmaleimide and anthracene.The results of spectrum,single crystal diffraction and theoretical calculation confirm that the single crystal of this kind of adduct benefits from through space conjugation and inter/intra molecular force,which ensures the dual,strong emission of fluorescence/phosphorescence.Furthermore,the study of homomorphic polycrystals obtained by diffusion method shows that the strong space conjugation and electron delocalization can increase the phosphorescence,especially the phosphorescence lifetime.After introducing hydrogen bonds,the enhanced luminescent intensity and longer lifetime prove that hydrogen bond can promote the conformational rigidity and ISC process,reduce the energy level difference between singlet and triplet,and fluorescence/phosphorescence dual emission.This research has paved a new way for the molecular design of pure organic p-RTP materials,specially such luminescent materials with heteroatoms as O/N and C=O groups,and been expected to be applied in the fields of anti-counterfeiting,biological imaging,etc.