Roles of nitrogen functionalities in enhancing the excitation-independent green-color photoluminescence of graphene oxide dots

Abstract

Fluorescent graphene oxide dots (GODs) are environmentally friendly and biocompatible materials for photoluminescence (PL) applications. In this study, we employed annealing and hydrothermal ammonia treatments at 500 and 140 °C, respectively, to introduce nitrogen functionalities into GODs for enhancing their green-color PL emissions. The hydrothermal treatment preferentially produces pyridinic and amino groups, whereas the annealing treatment produces pyrrolic and amide groups. The hydrothermally treated GODs (A-GODs) present a high conjugation of the nonbonding electrons of nitrogen in pyridinic and amino groups with the aromatic π orbital. This conjugation introduces a nitrogen nonbonding (n) state 0.3 eV above the oxygen nonbonding state (n state; the valence band maximum of the GODs). The GODs exhibit excitation-independent green-PL emissions at 530 nm with a maximum quantum yield (QY) of 12% at 470 nm excitation, whereas the A-GODs exhibit a maximum QY of 63%. The transformation of the solvent relaxation-governed π* → n transition in the GODs to the direct π* → n transition in the A-GODs possibly accounts for the substantial QY enhancement in the PL emissions. This study elucidates the role of nitrogen functionalities in the PL emissions of graphitic materials and proposes a strategy for designing the electronic structure to promote the PL performance.

<p>Amino-Functionalized Nitrogen-Doped Graphene Quantum Dots for Efficient Enhancement of Two-Photon-Excitation Photodynamic Therapy: Functionalized Nitrogen as a Bactericidal and Contrast Agent</p>

“…To verify that ROS were involved in the PDT effect of the amino-N-GQDs, we used α-tocopherol for ROS neutralization. 13 This step reduced the quantity of the generated ROS, and we discovered an increase in cell viability, as expected. Inadvertent exposure of the amino-N-GQDs to white light would have led to the production of 1 O 2 and O 2 .…”

“…Moreover, the values observed for the amino-N-GQDs are consistent with those reported in the literature (0.340-0.403 nm). 12,13 The XRD results also indicated that the basal plane was not considerably functionalized. This finding is in agreement with the theories that graphene has considerably more active edges than in-plane carbons do and that functional groups are present at the amino-N-GQD edges.…”

“…This finding is in agreement with the theories that graphene has considerably more active edges than in-plane carbons do and that functional groups are present at the amino-N-GQD edges. 13 The large basal spacing of the amino-N-GQD material can be attributed to the accommodation of several oxygen species, such as epoxy, hydroxyl, and amino groups, and the alteration of the carbon hexahedron grid plane, which resulted in increased graphene layer spacing. Raman spectroscopy was conducted for the GQDs.…”

Effect of nitrogen atom positioning on the trade-off between emissive and photocatalytic properties of carbon dots

“…In all cases, the nitrogen incorporation leads to substantial changes in the electronic properties of the CDs 38 – 43 . Similar effects were also seen in graphene oxide-based dots 44 , 45 . In particular, graphitic N atoms have a strong n-doping effect due to the additional π ∗ electrons, while pyridinic and pyrrolic N atoms have a weak p-doping character 46 .…”

Amino-Functionalized Nitrogen-Doped Graphene-Quantum-Dot-Based Nanomaterials with Nitrogen and Amino-Functionalized Group Content Dependence for Highly Efficient Two-Photon Bioimaging

“…Graphene oxide was prepared from a natural graphite powder (Bay carbon Inc., Bay City, MI, USA) using a modified Hummers' method [10,[37][38][39][40]. Graphite (8.5 M) and NaNO 3 (0.6 M) (Merck & Co., Kenilworth, NJ, USA) were mixed with H 2 SO 4 (FUJIFILM Wako Chemicals USA Inc., Richmond, VA, USA).…”