Synthesis And Mechanofluorochromic Properties Of Salicylaldimine Difluoroboron Complexes

Mechanofluorochromic(MFC)dyes is a kind of ‘smart’ materials whose solid emission is in response to external forces,including stretching,grinding,pressing and shearing.Meanwhile,the changes of the emitting colours were reversible by the treatment of grinding/fuming or annealing.As we all known,for the materials used for testing purposes,their luminescent spectrums are superior to the absorption spectrums due to less interference,higher sensitivity.They have potential applications in mechanical sensors,fluorescence writing and memory,camouflage and security materials.organoboron compounds is one of important fluorescent dyes,which has many advantages in both luminescence and structure such as high fluorescence quantum yield,coordinated and modified easily.Salicylaldehyde schiff bases are important fine chemicals intermediate as well as ligands,which have been widely used in many fields such as medicine,biology,materials and so on.Therefore,we designed and synthesized carbazole and triphenyl amine modified salicylaldimine difluoroboron complexes with different functional groups.Their MFC properties were also well investigated.We obtained some creative results.Details are outlined below:(1)A series of new salicylaldimine difluoroboron complexes bearing carbazole moieties were synthesized.It was found that the substituent groups on carbazole and in benzene rings of salicylaldimine had effect on their intramolecular charge transfer(ICT)emission.Interestingly,the synthesized difluoroboron complexes could emit strong light in solid states under UV irradiation and exhibited reversible mechanofluorochromism.For instance,the emission at 488 nm for the pristine sample of TCH red-shifted to 571 nm upon grinding,and the ground powder with orange emission could be turned into the solid emitting bluish-green light when fumed with DCM or heated at 200 ?C for 2 min.It should be noted that the shift of 83 nm for the emission band for the dye during MFC process was seldom reported in metallic-free organic compounds.XRD patterns illustrated that the Phase change between crystalline states and amorphous states was reasonable for the mechanofluorochromism.These MFC emitters based on salicylaldimine difluoroboron complexes may have potential applications in mechanical sensors,security printing and data-storage.(2)Triphenylamine functionalized salicylaldimine difluoroboron complexes containing different substituents have been synthesized.Their photophysical properties in the solutions and solids were investigated,it was found that the fluorescence of these complexes can be well-tuned by the introduction of substituents.These complexes exhibited intramolecular charge transfer(ICT)emission and solvatochromism.TH,TB,TT,TO displayed reversible MFC behaviors.For instance,after grinding the emission for the pristine sample of TH red-shifted from 551 nm to 600 nm.While the emission of TB red-shifted from 545 nm to 610 nm upon grinding.However,fumed with DCM or heated at 150 ?C for 1 min,the ground powder with orange emission could be turned into yellow light.The absorbance of solids red-shifted upon grinding,this may be the result of planarization.XRD and DSC demonstrated the transformation between crystal to amorphous state was reasonable for the MFC properties.Nonplanar structure of Triphenylamine and Donor-π-Acceptor electronic structure is important condition for mechanofluorochromic characteristics.