Mesoporous collapsing encapsulated carbon dots: Direct evidence for the effect of multiple-confined interactions of silica on efficient long-lived phosphorescence

Coupling with a matrix is the common strategy to improve the phosphorescence performance of carbon dots (CDs). However, there is a lack of clear and direct evidence about the formation mechanism of the inner relationship between CDs and matrix, and the specific effect of matrix on the phosphorescence performance. Mesoporous silica nanospheres (MSNs) were used as the research model to provide the direct evidence of the dense structure formation process and to construct a quantum chemical theoretical computational model of the effect of dense matrix on phosphorescence performance. Due to the multiple domain-limiting effects of rigid Si-C covalent bonds and SiO2 dense structure, the calcined-carbonized polymer dots-mesoporous silica nanospheres (C-CPDs-MSNs) can exhibit thermally activated delayed fluorescence (TADF) by tuning the HOMO-LUMO gap and enriching the electrons in the surface region. With a long lifetime of 3.07 s, the composite can also maintain stable phosphorescence performance under harsh conditions and has been successfully applied in multilevel information encryption, fingerprint identification, and cellular imaging. This work provides the direct evidence for the process of dense SiO2 structure enhancing the phosphorescence performance of CDs and offers a general strategy and method for the design and preparation of efficient and practical CDs-based phosphorescent materials.