Carbon Dots-Stimulated Amplification of Aggregation-Induced Emission of Size-Tunable Organic Nanoparticles.

Carbon dots (CDs)-induced microstructural modulation and amplification of emission intensity of self-aggregated fluorescent organic nanoparticles (FONPs) is a challenging task since CD is a well-known fluorescence quencher. In the present study, we have designed l-tyrosine-tagged hydrophobically (C-10) tailored naphthalene diimide derivative (NDI-), which formed FONPs in tetrahydrofuran (THF)-water binary solvent mixture. NDI- exhibited aggregation-induced emission (AIE) at 580 nm (orange) up to = 70 vol % of water in THF via excimer formation in combination with intramolecular charge transfer (ICT) upon excitation at 350 nm. Beyond = 70 vol %, the emission intensity gradually reduced up to = 99 vol % due to poor water dispersibility of NDI- FONPs. Doping of hydrophobically (C-2 to C-11 alkyl chain) surface-functionalized CDs (CD--) within self-aggregates of NDI- FONPs at = 99 vol % resulted in the modulation of both morphology and emission intensity of resulting self-assembled nanoconjugate. In the presence of C-2 alkyl chain tethered CD, the emission intensity of FONP-CD nanohybrid got quenched compared to that of native NDI- FONPs. The emission intensity of NDI- FONPs markedly enhanced by 3.6- to 5.0-fold upon inclusion of C-6 and C-11 alkyl chain containing CDs, respectively. Increasing the alkyl chain length on CD surface facilitated the interchain hydrophobic interaction between the organic nanoparticles and surface-functionalized CDs to form larger CD-doped fused FONPs. The extent of ICT between π-donor and π-acceptor residues became more efficient to exhibit enhanced AIE due to the accumulation of more NDI- around CD surface through interchain hydrophobic interaction. The C-11 alkyl chain containing CD-integrated FONPs showed the brightest orange emission with superior aqueous stability. These water-dispersible, orange-emitting, cytocompatible NDI--CD- FONPs were explored for long-term bioimaging of mammalian cells.