Studies On Fluorescent Materials Based On Benzofuran Or Benzothiadiazole

Since Tang's group put forward the concept of aggregation induced emission(AIE)in 2001,AIE has become one of the new research fields and developed rapidly.The number of molecules with AIE character continues to expand,making the AIE mechanism more and more clear.On the other hand,by changing the traditional aggregation causing quenching(ACQ)molecules into AIE-active molecules,the application of AIE has been further broadened.In the part of introduction,we briefly reviewed the discovery and the mechanism of AIE phenomenon as well as the newly discovered AIE molecules.Several strategies for changing ACQ molecules into AIE molecules have also been discussed.Although the research field of AIE has been developed rapidly,some experimental phenomena still could not been fully understood.Based on the synthesis of organic compounds and the investigation of the photophysical properties,it is possible for organic chemists to develop new AIE-active molecules and elucidate some AIE's structure-property relationships that might be utilized back to guide the design and preparation of new AIE-active compounds with the optimized properties.Secondly,if the traditional ACQ molecules can be converted into AIE-active molecules by simple methods,the number of AIE-active molecules would be increased fast.Thirdly,introduction of cage compounds into the AIE molecules would make molecules unique and might present unexpected results.Based on these aspects,three parts of work have been done and some interesting results have been obtained.Firstly,three green-emitting compounds based on 2-aryl-3-cyanobenzofuran fluorophore tethered with AIE-active tetraphenylethene(TPE)were designed and synthesized.p-Methoxyphenyl(PMP)was respectively installed on 5-,6-,and 7-position of 2-aryl-3-cyanobenzofuran for systematically investigating the substituent effect on their photophysical properties in solutions,nanoparticles,films,crystalline,as well as powders.The ACQ problem arising from the ?-? stacking between 2-aryl-3-cyanobenzofurans was surmounted by covalently bonding TPE unit Thus,these compounds emitted green light in solids and the film quantum yield approached 50.1%.Red-shifted mechanochromism was observed for the cry'stalline state with a small crystal density.The best OLED performance was achieved by using the compound with PMP occupied on 6-position which possessed the longest efficient conj ugation lengthSecondly,various amino substitute benzothiadiazoles(Am-BTDs)are synthesized and their photophy'sical properties in different states(solution,film,crystal,and powder)are investigated.The unusual anti-Kasha's emission is observed for those compounds with strong electronic coupling effect between donor and acceptor which directly results in the white emission of those compounds in dilute solutions.Among these Am-BTDs,some of them can be utilized as fluorescent chemosensors in sensing gaseous ammonia,and some of them can be developed for detecting fluoride anion with high selectivity and high sensitivity.Moreover,ACQ is not observed for these compounds in solids.They are emissive in films,crystals and powders with high color purity and moderate efficiencies.The emission color could be tuned from yellow to red according to the varied amino groups.Furthermore,they can be used as emissive layer in organic light emitting diodesFinally,a fluorescent D-A-D' triad,composed of monocarbaborane,benzothiadiazole and triphenylamine,was synthesized.By replacing the monocarbaborane with phenyl,p-methoxyphenyl or 4-pyridinyl,three analogs were prepared for comparison.The monocarbaborane is an electron donating group based on the comparative analysis of NMR spectra and the systematic investigation of their photophysical properties.The triad emits bright-yellow light in THF solution with the highest quantum yield and the longest decay time among these compounds.It tends to form nanoparticles in aqueous THF solution.The in situ generated nanoparticles might be used to detect silver ion with high sensitivity and high selectivity.By holding the molecules via multiple C-H…? interactions as well as electrostatic forces between the tetraethylammonium cation and the cage,a sheet-like arrangement of the triad is formed in the solid state with the smallest crystal density that provides the maximal possibility of mechanofluorochromism from crystalline to ground form.Moreover,by doping the triad in PVK,a white OLED is approached.