Synthesis And Properties Of Carbazole Derivatives With Stimuli–Responsive Luminescence Properties

In recent years,the development of stimuli-responsive luminescent materials has been witnessed for their exceptional applications in photodynamic conversion,monitoring environment,and life sciences.Organic stimuli-responsive luminescent materials have been attracting much attention due to their flexible molecular structures,adjustable luminescent color,low cost,as well as good biocompatibility.D-A typed molecules are a kind of important candidates for the OFF-ON switched stimuli-responsive luminescent material due to the intramolecular charge-transfer effect.In this paper,carbazole or triphenylamine was chosen as the electron-donating group,benzene ring as the ?-bridge,dicyanovinyl group or 4-nitrile phenyl group as the electron acceptors,and octyl or isooctyl was the N-substituents.3-Bromocarbazole,3,6-dibromocarbazole or 1,3,6,8-tetrabromocarbazole was selected as the starting materials and a series of carbazole derivatives(o-CPSM/o-CPDM/o-CPTM,i-CPSM/i-CPTM,TTPA-CZ-PN/DTPA-CZ-DPN)were designed and synthesized.By varying the number of he electron-acceptor units in the molecule,the photophysical characteristics and the stimuli-responsive luminescence properties of the compounds were regulated correspondingly.The structure-property relationship of the above compounds was studied by means of photoluminescence spectra,UV-vis absorption spectra and Transient fluorescence spectra,X-ray diffraction patterns,Differential Scanning Calorimetry and scanning electron microscope.The results are listed as follows:1.For the molecules with octyl N-substituents and malononitrile electron acceptors,with the increase of the number of electron-acceptor units,the fluorescence quantum yield in toluene was increased from 13.6% of single-armed o-CPSM to 35.7% of the tetra-armed o-CPTM,with the emission wavelength maintaining at around 500 nm.All of the compounds showed mechanoresponsive luminescence enhancement properties upon grinding and thermoresponsive luminescence decrease properties upon heating,of which the di-armed o-CPDM/the tetra-armed o-CPTM exhibited the highest increased/decreased ratio,respectively.XRD,DSC,SEM characterization results revealed that the thermoresponsive luminescence decrease properties derived from phase transition,while the thermoresponsive luminescence decrease properties was attributed to different stacked forms.2.For the counterparts with a branched N-substitution(isooctyl group)the contract ratio of mechanoresponsive luminescence was reduced(the photoluminescence quantum yields was increased by 2.16 times upon grinding for i-CPDM),while that of thermoresponsive luminescence was increased(the photoluminescence quantum yields is decreased to 0.29 times upon heating for i-CPTM.Single crystal X-ray diffraction results showed that the suppressed intermolecular interactions by the isoctyl groups with larger steric hindrance might be the reason for the results above.3.For the tetra-armed carbazole derivatives with 4-nitrile phenyl group as an electron-acceptor and triphenylamine as the electron-donor,the fluorescence quantum yield in toluene solution was increased from 39.82% of DTPA-CZ-DPN to 45.68 of TTPA-CZ-PN with the increased number of the donors.The contract ratio of thermoresponsive luminescence was increased by increasing the number of the electron-acceptors with planar structures.