Preparation And Properties Of Highly Efficient Organic Fluorescent Nanocrystals

Organic nanocrystals show good application potential in frontier fields such as bioimaging and photodynamic therapy,due to their good stability and excellent luminescence properties.However,organic fluorescence materials often suffer from fluorescence quenching in the aggregated state,which reduces their luminescent properties and severely limits their practical applications.Recently,aggregation-induced emission(AIE)materials have attracted extensive attention of researchers because of their high luminescence efficiency in the aggregated state.Here,we fabricated crystalline and amorphous fluorescent nanoparticles with different morphologies and luminescence properties through using amphiphilic polymer.The luminescence properties of nanoparticles was strongly depended on their morphologies,where the crystalline nanoparticles exhibit higher photoluminescence quantum yield than that of amorphous state.These nanoparticles show the potential application in the fluorescent imaging of Hela cells.The research contents are as follows:1.Preparation and properties of organic fluorescent nanocrystals with high efficiencyA distyryl anthracene derivative(TFMDSA molecule)with AIE properties was designed and synthesized.First,amorphous fluorescent nanoparticles TFMDSA NPs with spherical morphology were prepared by reprecipitation method,and the fluorescence quantum yield was 6.67%.When two amphiphilic polymers,m PEG_5K-PLLA_10K and m PEG_5K-PCL_10K with good biocompatibility,and TFMDSA molecules were used to prepare fluorescent nanoparticles by"one-pot"phacoemulsification,highly fluorescent quantum particles with bulk morphologies were obtained.The yields of fluorescent nanocrystals m PEG_5K-PLLA_10K@TFMDSA NCs and m PEG_5K-PCL_10K@TFMDSA NCs were 40.13%and 10.40%,respectively.Through the study of its photophysical properties,it was found that after the formation of nanocrystals,the radiative transition rate increased significantly,showing bright yellow-green fluorescence.In addition,through the study of their assembly mechanism,it was found that the hydrophobic side chains of the two amphiphilic polymers can effectively enhance the supramolecular interaction with TFMDSA molecules,thereby inducing the formation of stable crystalline arrangements.Cell imaging experiments show that,compared with amorphous fluorescent nanoparticles,highly luminescent fluorescent nanocrystals show better cell imaging effects.2.Preparation and properties of near-infrared emitting organic fluorescentnanocrystalsTB molecules with near-infrared luminescence properties were designed and synthesized.First,amorphous nanoparticles TB NPs with spherical morphology were obtained by reprecipitation method with a fluorescence quantum yield of only 0.75%.Second,the amphiphilic polymers m PEG_5K-PLLA_10K and m PEG_5K-PCL_10K were co-assembled with TB molecules by a"one-pot"phacoemulsification method to obtain near-infrared luminescent nanocrystals(m PEG_5K-PLLA_10K@TB)with bulk morphologies.NCs and m PEG_5K-PCL_10K@TB NCs),the emission wavelengths were602 nm and 642 nm,and the fluorescence quantum yields were 5.04%and 2.73%,respectively.The study of photophysical properties shows that compared with amorphous nanoparticles,molecular crystallization can greatly increase the radiative transition rate,improve the fluorescence quantum yield,and achieve strong near-infrared fluorescence emission.Aiming at the research on the assembly mechanism of nanocrystals,it was found that the hydrophobic side chain of this special amphiphilic polymer can also effectively enhance the supramolecular interaction with TB molecules,thereby inducing the formation of crystalline organic nanocrystals.Compared with almost non-luminescent amorphous nanoparticles,TB fluorescent nanocrystals can emit bright near-infrared fluorescence,showing good cell imaging effect.