Polymerization‐Driven Photoluminescence in Alkanolamine‐Based C‐Dots

Abstract

Carbonized polymer dots (CPDs), a peculiar type of carbon dots, show extremely high quantum yields, making them very attractive nanostructures for application in optics and biophotonics. The origin of the strong photoluminescence of CPDs resides in a complicated interplay of several radiative mechanisms. To understand the correlation between CPD processing and properties, the early stage formation of carbonized polymer dots has been studied. In the synthesis, citric acid monohydrate and 2‐amino‐2‐(hydroxymethyl)propane‐1,3‐diol have been thermally degraded at 180 °C. The use of an oil bath instead of a more traditional hydrothermal reactor has allowed the CPD properties to be monitored at different reactions times. Transmission electron microscopy, time‐resolved photoluminescence, nuclear magnetic resonance, infrared, and Raman spectroscopy have revealed the formation of polymeric species with amide and ester bonds. Quantum chemistry calculations have been employed to investigate the origin of CPD electronic transitions. At short reaction times, amorphous C‐dots with 80 % quantum yield, have been obtained.

Thermal Induced Polymerization of l‐Lysine forms Branched Particles with Blue Fluorescence

“…[ 29,30 ] In the light of this, the new band between 320 and 360 nm is barely explainable by the formation of the amide groups after dehydration and polymerization of l ‐lysine units. Similar absorption features are identifiable in the polymeric condensation of citric acid and amino rich molecules, such as tris(hydroxymethyl)aminomethane (Tris) [ 31 ] or ethylenediamine (EDA). [ 32 ] In these works, the polymeric structure is supported by the formation of amino groups units.…”

Towards N–N-Doped Carbon Dots: A Combined Computational and Experimental Investigation

“…Among bottom-up approaches, the hydrothermal method provides an efficient and scalable route to synthesize carbon particles at milder conditions from organic acids, amines, saccharides and their derivatives [26,27]. In this case, the proposed formation mechanism of CD is related to polymerization, aromatization, nucleation and growth of precursors in the water medium [27][28][29][30][31][32][33][34]. A comparable mechanism was also reported for other bottom-up synthesis [35].…”

Highly Photostable Carbon Dots from Citric Acid for Bioimaging

“…Both the CAArg and CATris dots, however, were synthesized by a hydrothermal synthesis that involves the carbonization of N-source precursors. Thermally synthesized CATris dots show a molecular-like fluorescence, which has been already correlated to the formation of polymeric species bearing amide and ester bonds [ 12 ]. Correspondingly, the formation of polymeric species assisted by arginine is the origin of the fluorescence in CAArg [ 21 ].…”

“…C-dots were synthesized from citric acid following two known routes with some modifications: one reacting citric acid with tris (hydroxymethyl) methyl aminomethane (CATris) [ 12 , 13 , 14 ] and a second one reacting citric acid with arginine methyl ester (CAArg) [ 15 ] in a stainless-steel hydrothermal reactor (25 mL volume) with a Teflon reaction vessel. The reactants were sonicated up to complete dissolution in 10 mL of deionized water, transferred in the autoclave, and then placed in a muffle (Ney, Vulcan 3-550) at 200 °C for 14 h for CATris and 6 h for CAArg ( Figure 1 ).…”