Molecular Fluorophores Self-Organize into C-Dot Seeds and Incorporate into C-Dot Structures

Abstract

Various molecular fluorophores have been identified to be present during carbon-dot (C-dot) syntheses. However, the organization of such fluorophores in C-dots is still unknown. We study the self-assembly of 5-oxo-1,2,3,5-tetrahydroimidazo-[1,2-α]-pyridine-7-carboxylic acid (IPCA), a molecular fluorophore present during the synthesis of C-dots from citric acid and ethylenediamine. Both forms of IPCA (neutral and anionic) show a tendency to self-assemble into stacked systems, forming seeds of C-dots during their synthesis. IPCA also interacts with graphitic C-dot building blocks, and fragments easily incorporates into their structures via π-π stacking.Both IPCA forms are able to create ad-layers internally stabilized by an extensive hydrogen bonding network, with an arrangement of layers similar to that in ordinary graphitic C-dots. The results show the tendency of molecular fluorophores to form organized stacked seeds of C-dots and incorporate into C-dot structures. Such noncovalent structures can be further covalently interlinked via the carbonization process during C-dot growth.

Carbon nano-dot for cancer studies as dual nano-sensor for imaging intracellular temperature or pH variation

“…S12 B). Similar results were also derived by Langer et al 36 from their theoretical studies on citric acid based CNDs.…”

Absorption and emission of light in red emissive carbon nanodots

“…Recently, self-assembly of a molecular uorophore, namely 5-oxo-1,2,3,5-tetrahydroimidazo-[1,2-a]-pyridine-7carboxylic acid (IPCA), has been shown to form an organized stacked blue emissive CND like structure. 53 It is interesting to point out here that, although the QY of red emission is much lower ($9.1%) than the blue emission ($54.7%), the emission spectral behavior and the QY of the as-synthesized crude sample is largely dictated by the large amount of the red emissive uorophore ($80%) present in the synthesis mixture in comparison to the very small amount of the blue component ($7%).…”

Contribution of the Molecular Fluorophore IPCA to Excitation-Independent Photoluminescence of Carbon Dots

“…22,23 Molecular dynamics (MD) simulations of noncovalent coassembly of IPCAs and CD fragments revealed that the MF molecules were not only stacked on solvent- exposed aromatic carbons of CDs but also incorporated into the CDs' structure. 15 The PL of CA-based CDs may therefore depend strongly on changes in the electronic structure of MFs induced by interactions with the local environment within the CD as well as interactions between luminescent centers. The diameters of complete CD/MF systems are typically around 2.8 nm, making them too large to be studied using highly accurate quantum mechanical (QM) methods.…”

“…3 Here, we study the PL of a CD-embedded IPCA molecules using a computationally affordable hybrid quantum mechanical/ molecular mechanical (QM/MM) 24,25 approach together with reliable CD structural models obtained from MD simulations probing the self-assembly of MFs and CD fragments. 15 Our QM/MM approach applying density functional theory (DFT) to describe the QM region was carefully benchmarked against more accurate theoretical approaches as well as experimental data on hydrated IPCA molecule. After being validated in this way, it was used to calculate the excitation and emission spectra of IPCA in various structural configurations within CD models.…”