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DOI: 10.1002/adma. 201604436 well-developed polymer hole transport layer (HTL) commonly used in optoelectronic devices has been used in CD-based electroluminescent LEDs.[20–23] However, a clear physical mechanism underlying the electroluminescence (EL) emission from CDs in the device or the origin of the EL emission has not been directly demonstrated due to the interference of the EL from HTL. In addition, the performance of these LEDs such as the maximum luminance (Lmax) and current efficiency (ηc) is still too low. There is no doubt that the best approach for realizing CDs-based electroluminescent LEDs is to achieve high-quality bandgap fluorescent carbon quantum dots (BF-CQDs). In this work, we report the first demonstration of bright multicolor bandgap fluorescent CQDs (MCBF-CQDs) from blue to red with a QY up to 75% for blue fluorescence. This was achieved by the successful solvothermal synthesis of the MCBF-CQDs by simply controlling the fusion and carbonization of citric acid (CA) and diaminonaphthalene (DAN) with a unique amino-substituted rigid carbon skeleton structure. Significantly, as-prepared MCBF-CQDs are nitrogen doped, highly surface-passivated, and have a high degree of crystallinity. As a direct benefit of the bandgap emission, the first example of monochrome electroluminescent LEDs with stable emission color from blue to red based on MCBF-CQDs directly used as an active emission layer without HTL has been realized. The LEDs show very stable and voltage-independent emission color. The Lmax reached 136 cd m− 2 for blue LEDs, which represents the best performance for CQDs …