Construction of Pure Organic Room Temperature Phosphorescent and Fluorescent Imaging Dyes Based on Donor-acceptor System

Author:Chen Biao

Supervisor:zhang guo qing


Degree Year:2018





Luminescent materials have broad important application in the fields of photoelectric,lighting,display,chemical sensing,anti-counterfeiting materials and biological imaging.Traditional phosphorescent materials,which are expensive and both toxic to the environment and organisms,are usually complex materials containing transition metals.Pure organic room-temperature phosphor is rare although pure organic small molecule has great application potential in that it has the advantages of easy synthesis,low cost and low toxicity.To effectively obtain pure organic room-temperature phosphorescence,it is necessary to have an effective singlet-triplet intersystem crossing(ISC).For most organic systems,the difference in energy levels between 1π-π*and 3π-π*is often very large,hindering the effective ISC process.In addition,fluorescent probes are very important in biomedicine detection,but outstanding fluorescent probes are rare,so a variety of new excellent probes are needed.During the course of my Ph.D.sdudy,I have been devoting myself to the study of pure organic room-temperature phosphorescent materials,new functional fluorescent probes and their applications.Because of the special photophysical properties of the charge transfer molecules,the design of these new materials is based on the donor-acceptor(D-A)system.Room-temperature phosphorescence(RTP)from purely organic molecules is important in applications such as sensing,imaging and illumination.Herein,we report a general strategy to construct organic phosphors(as solid-state solutes or solids)via attachment of donor and acceptor moieties to the same sp3 carbon atom.For such non-conjugated geminal systems,two distinct photophysical properties arise,in comparison to π-conjugated counterparts:1)a forbidden charge-transfer state normally occurs as the lowest singlet excited state,as a result of the nearly orthogonal molecular orbitals dictated by the sp3 carbon;2)the fluorescence(F)from either the donor or acceptor moiety is weakened to give balanced F/RTP ratios,feasible for luminescence ratiometric sensing and imaging applications.The system thus serves as a general molecular motif for promoting room-temperature phosphorescence as evidenced by spectroscopic data and it broadens the scope for organic phosphor design.A π-conjugated quinoline derivative with an N,N-hydroxyethylamino substituent group was synthesized and characterized via fluorescence spectroscopy.In organic solvents,the dye molecule exhibits solvatochromic fluorescence originated from an intramolecular charge transfer state.In aqueous solution,however,the dye becomes fluorogenic upon contact with biomacromolecular substrates such as cellulose,nuclear acids and proteins.The color of the bound quinoline strongly depends on the properties of the substrates and is sensitive to the pH in the environments.As a cell imaging agent,the quinoline derivative is found to stain differently for various subcellular components.Detailed spectroscopic analysis of the protein-bound quinoline dye suggests that the changes in conformation and protonation state may be responsible for the multicolor emission observed in life cells.The quinoline derivative has demonstrated great potentials as a single-component,multicolor staining agent in fluorescence microscopy for biological systems.