Study On Room Temperature Phosphorescence Of Polylactide Based On Naphthalimide Derivatives

Room temperature phosphorescence(RTP)materials are characterized by their long-lived triple excitons and larger Stokes shift,and are widely used in sensing,imag-ing,display,data encryption,and so forth.The inorganic and organometallic complexes currently mainly used in phosphorescent materials have the disadvantages of high cost,limited resources and high toxicity,thus spawning relatively environmentally friendly and easily modif-ied metal-free organic RTP materials.Polymer materials have more application value than small molecules because of their excellent flexibility,easy pro-cessing,and high thermal stability,and the unique rigid matrix can limit the vibration and rotation of molecules and thermal decay pathways.The chromophore is chemically connected to the polymer,and the resulting polymer material has the advantages of photoluminescence and processing performance.Therefore,the polymer RTP material is an ideal substitute for low molecular weight organic RTP compounds.1.The molecules of 4 naphthalimide derivatives and 3 naphthalene tetracarb oxylic diimide(NTCDI)derivatives were designed and synthesized:2-butyl-6-(2-hy droxyethoxy)-1H-benzo[de]isoquinoline-1,3(2H)-dione(NI-OH),2-butyl-6-((2-hydro xyethyl)thio)-1H-benzo[de]isoquinoline-1,3(2H)-dione(NI-SH),2-(9-ethyl-9H-carbaz ol-3-yl)-6-(2-hydroxyethoxy)-1Hbenzo[de]isoquinoline-1,3(2H)-dione(CZ-NI-OH),2-(9-ethyl-9H-carbazol-3-yl)-6-((2-hydroxyethyl)thio)-1H-benzo[de]isoquino-line-1,3(2 H)-dione(CZ-NI-SH),2,7-bis(2-hydroxyethyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone(NEG),2,7-bis(4-(2-hydroxyethoxy)phenyl)benzo[lmn][3,8]phenan throline-1,3,6,8(2H,7H)-tetraone(NBOH)and 2,7-bis(4-((2-hydroxyethyl)t-hio)phen yl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone(NBSH).The nuclear ma gnetic resonance(NMR)spectra were used to verify the correctness of these struc tures.Electrochemical methods were used to compare the electron donating ability of these small molecules.Among them,the molecules of CZ-NI-OH,CZ-NI-SH and NBOH and NBSH have intramolecular charge transfer state.2.NI-OH,NI-SH,CZ-NI-OH and CZ-NI-SH were used to initiate the polymeri-zation of D-L-lactide,respectively,and a series of PLA materials with photolumines-cence properties were synthesized:NI-O-PLA,NI-S-PLA,CZ-NI-O-PLA and CZ-NI-S-PLA.Among them,NI-O-PLA and NI-S-PLA are mainly fluorescence emission.By contrast,CZ-NI-O-PLA and CZ-NI-S-PLA with donor-acceptor structure are mainly phosphorescent emission at room temperature.CZ-NI-O-PLA has a long-lived phos-phorescence emission lifetime(maximum lifetime ?=407ms),and CZ-NI-S-PLA has a brighter red phosphorescence emission with a lifetime of 54.3ms.we also found that O and S will have different effects on the phosphorescence emission of this system.3.The dihydroxy chromophores NEG,NBOH and NBSH are connected to the L-polylactide chain,respectively,to obtain NEG-PLA,NBO-PLA and NBS-PLA.NEG-PLA is a dual-emission material,mainly blue-green fluorescent emission,while the fluorescent emission of NBO-PLA and NBS-PLA is weak or even invisible to the naked eye,and red phosphorescence emission will appear in vacuum,the lifetime is about 30 ms,which is slightly longer than the phosphorescence lifetime(<10 ms)of conventional pure organic RTP,new red phosphorescent units are prepared;by chang-ing different substituent groups,the fluorescence/phosphorescence emission ratio of such luminescent materials can be adjusted.The phosphorescence emission ratio is in-creased from 0.95:0.05 in NEG-PLA to 0.20:0.80(NBO-PLA)to 0.12:0.88(NBS-PLA).The influence of D,L-PLA and L-PLA on RTP emission were compared quali-tatively.The RTP emission brightness of D,L-PLA was brighter,while the emission wavelength of L-PLA was relatively longer.