Wide emission shifts and high quantum yields of solvatochromic carbon dots with rich pyrrolic nitrogen

Carbon dots (CDs) with solvatochromic emission colors in different solvents have attracted much attention as a new class of luminescent nanomaterial owing to their facile synthesis and low production cost. In this work, we prepared two kinds of CDs with solvatochromic emissions: green emission CDs (G-CDs) and multicolor emission CDs (M-CDs). G-CDs synthesized from o-phenylenediamine exhibited weak photoluminescence emission (quantum yield 2.8%-6.1%) and 39 nm solvatochromic shifts (492-531 nm). In contrast, M-CDs prepared from o-phenylenediamine and 4-aminophenol showed 87 nm solvatochromic shift range (505-592 nm) and much higher photoluminescence quantum yield (18.4%-32.5%). The two CDs exhibited different emission, absorption, and photoluminescence lifetime. The origin of solvatochromic shifts and the formation mechanism of CDs were demonstrated by analyzing the structures and compositions of two CDs. High percentages of pyrrolic nitrogen and amino nitrogen make wider solvatochromic shifts and higher quantum yields. The results were well supported by density functional theory calculations. This effective strategy to expand solvatochromic shift range and improve quantum yields could open a new window to prepare satisfied solvatochromic carbon dots.