Achieving Color‐Tunable Solid‐State Fluorescence by Adjusting the Molecular‐State Chromophores on Carbonized Polymer Dots

Carbon dots (CDs) have attracted great interest in recent years due to their excellent fluorescent properties, convenient synthetic methods, and wide availability of source materials. However, although most CDs exhibit excellent luminescent properties in solution, achieving solid‐state fluorescence (SSF) CDs is still difficult due to aggregation‐caused quenching, and realizing color‐tunable SSF‐CDs remains a serious challenge. Herein, the SSF‐carbonized polymer dots (CPDs) are successfully obtained by one‐step hydrothermal of polyethyleneimine (PEI) and citric acid. The photoluminescence centers of these CPDs are molecular‐state chromophores, which are proved as imidazo [1,2‐a] pyridine‐7‐carboxylic acid, 1,2,3,5‐tetrahydro‐5‐oxo‐ (IPCA) derivatives by NMR. Further investigation reveals that the formation and distribution of IPCA derivatives would affect the bandgaps when CPDs particles aggregate, which is also verified by density functional theory calculations. Based on the above conclusion, the blue, green, yellow, and orange SSF CPDs are successfully obtained, and the multicolor and white emission light emitting diodes are effectively fabricated by these CPDs.