Studies On Photophysical Properties Of Three Series Of Excited State Intramolecular Proton Transfer Fluorescence Molecules

Excited state intramolecular proton transfer?ESIPT?has received extensive attention due to large Stokes shift and facile structural modification.Based on its unique optical properties,ESIPT dyes can be well applied in various fields such as fluorescence imaging,fluorescent probes,electrochemistry,and organic light-emitting diodes,etc.Although ESIPT dyes have been widely used,the relationship between construction and photophysical properties is not clear and needs more in-depth research.The main research contents of this paper include three parts are as follows:1.Four 2-?2-hydroxyphenyl?benzothiazole?HBT?-based disubstituted derivatives,with substitutions at the 4'-and 5'-positions,were readily synthesized by the Suzuki coupling reaction,namely HBT-H-H?HBT-CN-CN?HBT-CN-H?HBT-CN-OMe.The rules of the influences of substituents to the photophysical properties were studied.The research result shows that introduction of an electron-withdrawing group at the 4'-position results in a red shift of the HBT.Thus,the electronic effect of substituents at the 5'-position is opposite to that at the 4'-position.Theoretical calculations demonstrate that the HOMOs is mainly distributed on the 5'-position phenyl,and the LUMOs more on the 4'-position phenyl.This result may provide experimental and theoretical basis for the design of new ESIPT dyes.2.Three pyrene derivatives modified with HBT were synthsized by Sonogashira coupling reaction?HBT-Py,2,6-dimethyl phenyl?DMP?-HBT-Py,and HBT-Py-DMP?.HBT-Py,although highly planar and strong?-?interactions between the pyrene moieties,show strong solid-state fluorescence in the monomeric state and excellent thermal stability.Based on these properties,HBT-Py behaves as an efficient solid emitter in OLEDs with 3%external quantum efficiency and 5.32 cd A^-1 current efficiency.Hence,this study provides an experimental basis for the application of ESIPT dyes in optoelectronic materials.3.In order to further studies the effect of the connecting mode on the optical properties of HBT,three nitrophenyl-modified HBT derivatives?HBT-s-NO₂,HBT-d-NO₂,and HBT-t-NO₂,respectively?,in which HBT and nitrophenyl moiety was connected with C-C,C=C,and C?C bonds between their,were synthesized by Suzuki,Heck,and Sonogashira coupling reaction,respectively.Only HBT-d-NO₂ exhibited strong positive enol-emission solvatochromism,and a solvent-polarity independent keto emission,which could be attributed to consecutive excited state intramolecular charge transfer?ESICT?–ESIPT reactions;however,similar photophysical properties were not observed for HBT-s-NO₂ and HBT-t-NO₂.In addition,although the highly planar HBT-d-NO₂ is H-aggregated,it still exhibits high fluorescence efficiency?40.55%?in the crystalline state due to strong intramolecular H-bonds.This study provides new insight for the design of ESICT/ESIPT coupled systems,and for engendering planar dipolar molecules with excellent emission properties in the solid state.