Synthesis And Multifunctional Applications Of Long Wavelength Fluorescent Carbon Dots

Carbon dots(CDs),as novel carbon-based nanomaterials,have drawn merits owing to their narrow and tunable emission peaks,good biocompatibility,multitudinous application and low cost.Most of reported CDs show high quantum yield(QY)in blue and green spectral regions,but are easily absorbed by the biological tissue and disturbed by background interference,whose practical applications for bio-imaging are strictly limited,while bright long-wavelength(λem>600 nm)CDs are relatively lacked.What’s more,most of CDs undergo aggregation-caused fluorescence quenching(ACQ)effect in powders because of excessive resonance energy transfer(RET)or direct π-π*interactions.To overcome the drawback,the widely used method is to allow CDs to be incorporated into the appropriate solid matrices,like silica xerogel,starch,polymers and so on.But only a few reported CDs could conquer ACQ effect without solid matrices.Therefore,it is very meaningful to synthesize highly efficient longwavelength CDs and novel matrix-free aggregation-induced emission CDs.Here,three kinds of CDs were synthesized,and applied in different field according to the fluorescent characteristics as follows:1.Herein,red-emitting CDs synthesized by p-Phenylenediamine(pPD-CDs)exhibit a weak red band at 635 nm under the excitation at 450 nm.Adding(NH4)2HPO4 and KBr as P and Br precursors,P,Br-doped CDs(P,Br-CDs)show the red emission peak at 610 nm with a peak of blue-shift about 25 nm and a dramatic emission enhancement up to 20-folds compared to pPD-CDs.The QY of P,BrCDs was greatly improved to 11.3%from 0.55%.Furthermore,P,Br-CDs show a remarkable luminescent turn-off response after adding Cu2+.In addition,the quenched luminescence could be recovered by the chelation between Cu2+ and L-cysteine(L-Cys)after adding L-Cys.This fluorescence "ON-OFF-ON" protocol could be applied for sequent Cu2+ and L-Cys detection,and offer a linear range of 0150 μM and 0-100 μM with a limit of detection of 4.4 μM and 2.3 μM,respectively.All results indicate that P,Br-CDs are of great potential for further biological and environmental application.2.A facile one-step hydrothermal synthesis of highly-fluorescent red-emitting CDs(R-CDs)with QY of 37.2%.R-CDs exhibit a maximum emission band at 640 nm under the excitation wavelength of 500 nm.Furthermore,R-CDs show excitationdependent and solvent-engineered fluorescent characteristics that the luminescent properties could be greatly affected by polarity.Due to the sensitivity to polarity,a quick and precise approach for wide-range water detection in organic solvents has been developed.Because of the low autofluorescence background,R-CDs were applied to the zebrafish larvae imaging.Polarity-selective bright red light from R-CDs is seen in the low-polarity organs like yolk sac and eyes that contain abundant lipids and lipoprotein.Our results demonstrate that R-CDs could be used as bio-imaging agents and fluorescent sensors for quantitative and visual water detection in various organic solvents.3.Presently,CDs with aggregation-induced emission(AIE)are relatively rare and being a research hot-spot,since most of conventional CDs suffer severe quenching in solid state.Herein,novel CDs with solution and solid dual-state emission were obtained using dithiosalicylic acid and polyetherimide as precursors by a facile one-step hydrothermal synthesis,i.e yellow solvent-dependent fluorescence in solution state(λem=580 nm)and red AIE emission in solid state(λem=640 nm).CDs powder could be used as LED red phosphor and the fabricated WLEDs exhibit good performance:CRI=89.5,CCT=3876 K,CIE=(0.350,0.331).Furthermore,by using solventdependent phenomenon,AIE-CDs solution can be applied as the fluorescence sensor for sensitive quantitative detection of trace water in various organic solvents with high accuracy and sensitivity in wide linear range,in which R2 varies from 0.853 to 0.994 and a low detection limit is from 0.30%to 3.2%.This work provides a construction of novel dual-state emissive CDs with multi-functional applications in sensing and LED device.