Solvent Effect on Structural Elucidation of Photoluminescent Graphitic Carbon Nanodots

Abstract

Photoluminescence (PL) of carbon nanodots (CNDs) is proposed to originate from the polycyclic aromatic carbon-core and in situ synthesized molecular fluorophores. This work reports the CNDs prepared by direct pyrolysis of citric acid only at a prolonged time, 40 h, and their fluorescence emission parameters in a variety of solvents by steady-state and time-resolved emission spectroscopies. The response of fluorescence emission lifetime and emission quenching rate constants to changes in solvent parameters such as polarity and tumbling lifetime were essentially independent, unlike molecular fluorophores that display solvent-dependent emission parameters. Fluorescence emission was quenched in nitromethane additionally indicating to the polycyclic aromatic carbon-core as a predominant structural feature of the CNDs. The quenching of CND emission in the presence of benzophenone that has a strong triplet component in the excited state was observed. Quenching demonstrates the Stern–Volmer behavior and reveals the additional nonradiative decay pathways of CNDs. The main photophysical features of CNDs are discussed in terms of fluorescence emission originating from the excited state of the polycyclic aromatic carbon-core where contribution from the potential molecular fluorophores is considered minimal.

Ultrafast Interfacial Electron Transfer from Graphene Quantum Dot to 2,4-Dinitrotoluene

“…However, in our case, since both methanol and water are protic and completely miscible at any ratio, their mixture would behave more like a single component solvent. Unlike organic dye molecules, the band edge energy level of GQDs is not altered by the solvent heterogeneity, solvent local cluster formation, or synergistic effects of the binary solvent, which further confirms that the change of solvent from pure water to the water–methanol mixture would not affect the intrinsic PET rate of the GQD–DNT complex. − Shape, FWHM, and the peak positions of absorption and emission spectra of GQDs do not change much when transferred from neat water to the water–methanol mixture, indicating neither a solvent-induced aggregation of GQDs and thereby change in their respective energy levels, nor any structural change occurs. Like PL (steady state), the fluorescence lifetime of GQDs quenches significantly in the presence of DNT (Figure ).…”

Polarity-dependent emission from hydroxyl-free carbon nanodots

“…This is possibly due to the prevalence of some degree of mixing between the π* of C sp 2 domains with O and N-states. Higher λ ex enhanced the possibility of the excited electron transfer from C sp 2 domains to O, N-states, resulting in an increase in the emission intensity at 468 nm 63 (Fig. 3a and c).…”

Photoluminescent Carbon Nanodots Integrated Polymeric Materials in One Step from Molecular Precursors

“…CNDs were proposed to have composed of the π-conjugated polycyclic aromatic core with the carboxyl and carbonyl-functionalized groups at the edges. [9] It is conjectured that both the CA-EG and CA-PG have gone through the incomplete CA carbonization, at least to the level of CNDs, caused by a competing polymerization of the glycols. Contrarily, in case of both the CA-3EG and CA-3PG, a more efficient polyesterification reaction is demonstrated, which could indicate the carbonization of CA esters to form the ester analogs of the CNDs.…”

“…The CNDs were readily dispersed in a wide range of solvents. [9] The origin of PL emission of those CNDs was shown to originate mainly from the π-conjugated polyaromatic domains, where the contribution in PL emission of the molecular fluorophores that are synthesized at early stages were minimal. This work reports the single-step preparation of CNDs/polymeric materials starting from the citric acid and the ethylene glycol (EG) or propylene glycol (PG) as the only starting precursors.…”