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We clarified the chemical structure of typical “bottom-up” CDs and proved that IPCA is the molecular state photoluminescence center.

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Polymer carbon dots (PCDs) are proposed as a new class of room-temperature phosphorescence (RTP) materials. The abundant energy levels in PCDs increase the probability of intersystem crossing (ISC) and their covalently crosslinked framework structures greatly suppress the nonradiative transitions. The efficient methods allow the manufacture of PCDs with unique RTP properties in air without additional metal complexation or complicated matrix composition. They thus provide a route towards the rational design of metal-free RTP materials that may be synthesized easily. Furthermore, we find that RTP is associated with a crosslink-enhanced emission (CEE) effect, which provides further routes to design improved PCDs with diverse RTP performance. Our results show the potential of PCDs as a universal route to achieve effective metal-free RTP.

A new type of fluorescent material is presented, which is called non-conjugated polymer dots (NCPDs). The NCPDs only possess sub-fluorophores (which are groups such as C=O, C=N, N=O) instead of typical conjugated fluorophore groups, and thus these materials should not have strong photoluminescence (PL) in the usual sense. Nevertheless, the PL of these sub-fluorophores can be enhanced by chemical crosslinking or physical immobilization of polymer chains, which is named the crosslink-enhanced emission (CEE) effect. The significant advances achieved by us and other groups on both experimental and theoretical aspects are discussed, and the covalent-bond CEE, rigidity-aggregated CEE, or supramolecular CEE in NCPDs is elaborated. Moreover, synthetic strategies, unique optical properties, and the promise of NCPDs in bio-related fields, such as bioimaging and drug delivery, are systematically discussed.

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The crosslink enhanced emission (CEE) in a new type of non-conjugated polymer dots (PDs) is proved. The enhanced PL originates from the decreased vibration and rotation of amino-based chromophores. Furthermore, the cellular uptake mechanism and internalization of PDs were investigated in detail.