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Even after several years of research, controlled synthesis of photoluminescent carbon nanodots (C-dots) still constitutes a major challenge, and investigation of their photoluminescence (PL) mechanism remains elusive. Various top-down and bottom-up approaches have been reported lately. However, these methods usually suffer from limited control over the major factors that dictate the PL behaviour of these fascinating carbon materials. To this end, we discover a new approach to prepare C-dots from size-tunable single chain polymeric nanoparticles. Taking advantage of the state of the art living radical polymerization technique and unique features of Bergman cyclization, narrowly dispersed C-dots are prepared in a straightforward manner. PL study shows that the optimal emission wavelength of C-dots red-shifts when the size of C-dots decreases, which is different from the trends typically found in semiconductor quantum dots and C-dots prepared from graphitized materials. To clarify the PL mechanism of C-dots prepared from different sources, a theoretical study based on density functional theory is performed. Two series of model compounds, fused aromatic rings and cyclo-1,4-naphthylenes, are chosen for C-dots with different microstructures. The calculation data indicate that PL energy of C-dots is dictated by the size and microstructure of the sp2 carbon core. For a C-dot with a graphitized core, the smaller the size of the core, the higher the PL energy, while for a C-dot with an amorphous core, an inverse trend is revealed. Surface reduction experiments further show that the quantum yield of C-dots is controlled by the surface chemistry.

Hydrophilic polymeric nanoparticles are synthesized through a Bergman cyclization- mediated intramolecular chain collapse of structurally well-defined linear polymers, and then used as size-tunable nanoreactors to fabricate and encapsulate quantum dots in a one-pot reaction. Crystalline quantum dots are formed in all of these nanoreactors and visualized by transmission electron microscopy. Smaller nanoreactors produce one quantum dot each while larger nanoreactors form a number, resulting in fluorescence quenching. By controlling the molecular weight of the linear polymer precursor, a variable number of nanocrystals are fabricated and assembled in a single nanoreactor.

Polymeric nanoparticles were synthesized through Bergman cyclization mediated intramolecular chain collapse. Enediyne moieties were incorporated into linear polymers through copolymerization or post-polymerization modification. The resulted enediyne containing copolymers were then subjected to intramolecular chain collapse under ultra-dilute condition or applying a continuous addition technique. The occurrence of Bergman cyclization was confirmed with IR, NMR and DSC analysis. The intramolecular chain collapse was characterized with GPC, DSC, and AFM. Dramatic decreases of apparent molecular weights of linear copolymers were observed after Bergman cyclization. The structural diversity of enediyne precursors and mild chain collapse condition allow wide monomer selection, which facilitates preparation of a broad range of polymeric nanoparticles. Low-k dielectric thin films were prepared using polymeric nanoparticles through “porogen” approach. The packing tightness of polymeric nanoparticles showed strong influence on film formation behavior with MSSQ matrix. With tightly packed polymeric nanoparticles as sacrificial pore generators, thin films with dielectric constants of as low as 2.1 were obtained.