Mild bottom-up synthesis of carbon dots with temperature-dependent fluorescence

Bottom-up methods allowing the preparation of carbon dots (CDs) with favorable attributes are highly desirable. Herein, we report the mild bottom-up synthesis of CDs towards temperature sensing. Five kinds of CDs with blue or green fluorescence were synthesized in water or tetrahydrofuran (THF) under moderate conditions (normal pressure, 50~95 °C), with use of carbonyl compounds as carbon sources, such as acetylacetone (AA), cyclohexanone (CH), 2-hydroxy-2-methylpropiophenone (HM), glutaric dialdehyde (GD), and salicylaldehyde (SA). Typically, with use of acetylacetone (AA) as carbon sources, CDs were synthesized at 95 °C in water in the presence of zinc chloride and 1, 2-dichloroethane. The synthesis, characterizations, and optical properties of AA-derived CDs were thoroughly investigated. The resultant CDs exhibit green photoluminescence (PL) at 520 nm with absolute PL quantum yield (QY) of 21%. Moreover, the PL intensity proportionally depends on temperature in the range 150–360 K, which makes AA-derived CDs potentially useful for temperature sensing.