Synthesis,Photophysical Properties And Stimulus Response Of Difluoroboron Complexes Containing Tert-butylcarbazole

The development and application of organic luminous materials had been attracted much more attentions in recent year.To be notice,organic difluoroboron compounds as a kind of fluorescent dyes with unique optical performance,such as high quantum yields,high electron affinities,superior stimulus response performance,occupies broad markets in organic photoelectric materials’field.This paper was based on D-π-A difluoroboron compounds and intended to discuss the influence of functional group replacement for molecule’s properties,which contains the electronic structures,photophysical properties and the response for stimulus such as mechanical force,acid and amine vapors.The following creative results have been obtained:We synthesizedβ-diketone difluoroboron complexes HPC,BrPC,MeOPC and Me2NPC,which contains tert-butylcarbazole.These four complexes exhibited revisable mechanoluminescence（ML）under the operation of grinding and fuming with CH₂Cl₂and heating by machine.It is worth mentioning that the Me2NPC showed the opposite ML properties compare to HPC,BrPC and MeOPC,i.e.the Me2NPC sample’s emission exhibited weak blue-shift with 14 nm while HPC,BrPC and MeOPC showed obvious red-shift emission with 49 nm,38 nm and 30 nm to visible-light region.Thus,the introduce of electron-absorbing substituents and electron-giving substituents might be helpful for theβ-diketone difluoroboron complexes’ML behavior.Analysising the phenomenon,we think during the grinding of samples,HPC and BrPC changing from single molecule state to J-aggreates,MeOPC going through the relative intensity ofπ-πinteraction,while Me2NPC partly assembling to J-aggregates.P-XRD spectra showed that the reason for ML is the transformation between crystalline and amorphous states.Thus,HPC,BrPC,MeOPC and Me2NPC showed interesting turn-on fluorescent which was visible to the naked eye during the MLprocess.To be notice,electron-withdrawing substituents drove theseβ-diketone difluoroboron complexes express higher contrast performance.We synthesizedβ-diketone difluoroboron complexes 1HNC,2HNC and 6MeONC,which contains tert-butylcarbazole.We found that the replacement of naphthalene ring drove theβ-diketone difluoroboron complexes expressed higher contrast performance compared to the replacement of benzene ring.These three complexes exhibited sensitive and revisable ML under the operation of grinding and fuming with CH₂Cl₂and heating by machine.The emission spectra of 1HNC,2HNC and 6MeONC showed great red-shift with 44 nm,43 nm and 64 nm respectively,thus the introduce of methoxy may play an importane role in high-contrast ML performance.We think it is because methoxy that makes the loosely stacked complexes more untight so that the interaction of molecules become easily to change under external mechanical stimulus thus the higher contrast ML performance achieved.Through the UV-visible absorption spectra of different solid states test,we found the ML for 2HNC and 6MeONC originate from the transition of isolated molecule state to J-aggreates,which means that the as-synthesized sample existed in the crystalline state and then formed J-aggreate with the crystalline was broaken when they were being grind.1HNC formedπ-aggreates under different solid states with loose stacking,and it exhibited outstanding ML after grinding with the interaction within the molecule evidently enhanced.P-XRD test revealed the transition from crystalline to amorphous states during the ML process.These ML dyes based onβ-diketone difluoroboron complexes might have potential application value in fileds like mechanical sensors,secure printing and data storage.We synthesized N,O-cheated difluoroboron complexes QXC and QUC,which contains tert-butylcarbazole.Interestingly,these two complexes’coated film showed double response to both volatile acid vapors and organic amine vapors.The absorption spectrum and ¹H NMR before and after adding the TFA gave the reason for the quenching of the luminous of coated-film as following:the quenching of the luminous by volatile acid vapors was due to the protonation of complexes and the intramolecular photoinduced electron transfer（PET）in turn;the quenchment by organic amine vapors was through the weak molecule interactions between amine and the BF₂ unit of complexes which was electron-deficient.QXC and QUC exhibited excellent selectivity to acid and amine vapors when compared to the ordinary organic solvent vapors.For example,the coated-film of QXC in the detection of trifluoroacetic acid（TFA）and benylaniline vapors showed the decay time and the detection limit are 0.86 s,1.32 ppb and 1.78 s,67.2 ppb respectively;the coated-film of QUC in the detection of trifluoroacetic acid（TFA）and benylaniline vapors showed the decay time and the detection limit are 1.29 s,78.8 ppb and 2.95 s,0.218 ppm respectively.By contrast,the coated-film of QXC showed the more sensitive response to strong acid and aromatic amine vapors.