Tuning Emission Behavior Of A-?-D-?-A Type Of Red/Near-infrared Fluorescent Dyes Based On Carbazole

In recent years,red and near-infrared(NIR)fluorescent dyes have great application interests in photoelectric materials,biological imaging,fluorescent probe and information encryption.Developing red/NIR fluorescent dyes with a good luminous performance has become an urgent task for current scientific research.In this work,a series of A-?-D-?-A carbazole derivatives using dicyanovinyl groups,1,3-Indandione groups and tricyanofuran derivative(TCF)as the electron-accepting moieties,respectively,and differing in the N-hexyl(h-)and N-isooctyl substitute(i-)carbozale were designed and synthesized(h-CPDM / i-CPDM?h-CPBI / i-CPBI and h-CPBT / i-CPBT).Their UV-vis absorption spectra,photoluminescence spectra and fluorescence quantum yields in solutions,aggregations and solid states were systemly investigated,such as solvatochromism effect,aggregation caused quenching(ACQ),aggregationinduced emission(AIE)and mechanoresponsive luminescence(MRL).1.With the increasing of the electron-withdrawing ability of the acceptors,HOMO energy levels of the compounds were almost the same,but energy gaps(Egs)and LUMO energy levels decreased gradully.As a result,the emission wavelength red-shifted.2.h-CPDM / i-CPDM and h-CPBI / i-CPBI had remarkable solvatochromism effect,with emission color tuning from blue to orange-red for h-CPDM / i-CPDM and from blue to red for h-CPBI / i-CPBI by changing the solvent from nonpolar hexane to polar dimethyl sulfoxide,which could be ascribed to their intrinsic intramolecular charge chansfer characteristics(ICT).3.Compounds h-CPDM / i-CPDM and h-CPBI in THF and water mixture exhibited ACQ effect,which could be attributable to the unfavorable ?-? interactions between the molecules in the J-aggregates.Compound i-CPBI showed AIE effect in their J-aggregates,which can be attributed to the restrained the ?-? stacking interactions and limited the intramolecular rotation by the branched N-isooctyl substituent.4.All compounds exihibited remarkable MRL turn-on behaviors.After being ground,?Fs of h-CPDM and i-CPDM increased from 0.9%(?max 678 nm)and 0.3%(?max 661 nm)to 8.7%(?max 610 nm)and 25.6%(?max 596 nm),?Fs of hCPBI and i-CPBI increased from 0.6%(?max 713 nm)and 0.3%(?max 648 nm)to 18.6%(?max 625 nm)and 29.4%(?max 628 nm),?Fs of h-CPBI and i-CPBI increased from 0.82%(714 nm)and 0.85%(717 nm)to 5.41%(729 nm)and 5.27%(731 nm).The XRD,DSC and time-resolved emission-decay investigations revealed this mechanoreponsive luminescence turn-on could be ascribed to the disturbance of the ?-? stacking interactions in the non/weakly emissive Jaggregates by mechanical force.