Supramolecular interactions via hydrogen bonding contributing to citric-acid derived carbon dots with high quantum yield and sensitive photoluminescence

Zhang, Wenkai; Shi, Lijuan; Liu, Yingqiu; Meng, Xianghui; Xu, Hao; Xu, Yuanqing; Liu, Baoying; Fang, Xiaomin; Li, Hai‐Bei; Ding, Tao

doi:10.1039/c7ra02160g

Cited by 53 publications

(36 citation statements)

References 46 publications

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“…There is a lot of evidence supporting these ideas, as the similarity of the blue emission of cytrazinic acid at 420-440 nm to the blue fluorescence of many CDs obtained from citric acid [88,188], theoretical simulations [103,183], and the lack of tunability of the emission band of these CDs, in striking contrast with the behaviour of CD fluorescence excited at lower energies, which is strongly tunable [161].…”

Section: Emission Mechanismsmentioning

confidence: 99%

“…Among the amorphous varieties, another possible core structure has been recently proposed for some CDs synthesized by bottom-up procedures. This core structure involves the aggregation of small molecules which are formed usually during the carbonization of citric acid (a very popular precursos for CDs) [102,103], and kept together in a quasi-spherical shape by comparatively weak interactions, like π − π, H-bonds, Van der Waals.…”

Section: The Structure Of Cdsmentioning

confidence: 99%

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Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

2018

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Carbon dots (CDs) are an emerging family of nanosystems displaying a range of fascinating properties. Broadly speaking, they can be described as small, surface-functionalized carbonaceous nanoparticles characterized by an intense and tunable fluorescence, a marked sensitivity to the environment and a range of interesting photochemical properties. CDs are currently the subject of very intense research, motivated by their possible applications in many fields, including bioimaging, solar energy harvesting, nanosensing, light-emitting devices and photocatalyis. This review covers the latest advancements in the field of CDs, with a focus on the fundamental understanding of their key photophysical behaviour, which is still very debated. The photoluminescence mechanism, the origin of their peculiar fluorescence tunability, and their photo-chemical interactions with coupled systems are discussed in light of the latest developments in the field, such as the most recent results obtained by femtosecond time-resolved experiments, which have led to important steps forward in the fundamental understanding of CDs. The optical response of CDs appears to stem from a very complex interplay between the electronic states related to the core structure and those introduced by surface functionalization. In addition, the structure of CD energy levels and the electronic dynamics triggered by photo-excitation finely depend on the microscopic structure of any specific sub-type of CD. On the other hand, this remarkable variability makes CDs extremely versatile, a key benefit in view of their very wide range of applications.

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Section: Emission Mechanismsmentioning

confidence: 99%

Section: The Structure Of Cdsmentioning

confidence: 99%

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

2018

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“…Following precedent, we refer to these materials as CA carbon dots, or CACDs. [20] Several groups have tried to elucidate the structure of CACDs and understand the mechanism for their superior PL quantum yields. Some have conjectured that nitrogendoped polycyclic aromatic hydrocarbons or graphitized carbons are formed during synthesis and account for the enhanced PL compared with undoped carbon dots.…”

Section: Introductionmentioning

confidence: 99%

A molecular fluorophore in citric acid/ethylenediamine carbon dots identified and quantified by multinuclear solid‐state nuclear magnetic resonance

Duan

Zhi

Coburn

et al. 2020

Magnetic Reson in Chemistry

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The composition of fluorescent polymer nanoparticles, commonly referred to as carbon dots, synthesized by microwave-assisted reaction of citric acid and ethylenediamine was investigated by 13 C, 13 C{ 1 H}, 1 H─ 13 C, 13 C{ 14 N}, and 15 N solid-state nuclear magnetic resonance (NMR) experiments. 13 C NMR with spectral editing provided no evidence for significant condensed aromatic or diamondoid carbon phases. 15 N NMR showed that the nanoparticle matrix has been polymerized by amide and some imide formation. Five small, resolved 13 C NMR peaks, including an unusual ═CH signal at 84 ppm (1 H chemical shift of 5.8 ppm) and ═CN 2 at 155 ppm, and two distinctive 15 N NMR resonances near 80 and 160 ppm proved the presence of 5-oxo-1,-2,3,5-tetrahydroimidazo[1,2-a]pyridine-7-carboxylic acid (IPCA) or its derivatives. This molecular fluorophore with conjugated double bonds, formed by a double cyclization reaction of citric acid and ethylenediamine as first shown by Y. Song, B. Yang, and coworkers in 2015, accounts for the fluorescence of the carbon dots. Cross-peaks in a 1 H─ 13 C HETCOR spectrum with brief 1 H spin diffusion proved that IPCA is finely dispersed in the polyamide matrix. From quantitative 13 C and 15 N NMR spectra, a high concentration (18 ± 2 wt %) of IPCA in the carbon dots was determined. A pronounced gradient in 13 C chemical-shift perturbations and peak widths, with the broadest lines near the COO group of IPCA, indicated at least partial transformation of the carboxylic acid of IPCA by amide or ester formation.

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“…It has been known that hydrothermal reaction between CA and several amines forms highly emissive organic fluorophores such as citrazinic acid . Ding's group identified that a fluorescent organic fluorophore, 1‐(2‐aminoethyl)‐5‐oxo‐1,2,3,5‐tetrahydroimidazo[1,2‐a]‐pyridine‐7‐carboxylic acid (AEIOP) was synthesized during the hydrothermal reaction between CA and DETA . In their work, a mass peak at 224 m z −1 corresponding to [(AEIOP)H] + ion with a chemical formula of C 10 H 14 N 3 O 3 + was observed, and the molecule was a main component of luminescent fraction when they eluted CD product by chromatography.…”

Section: Resultsmentioning

confidence: 99%

Quenching‐Resistant Polymer Carbon Dot Preserving Emission Color Consistency in Solid‐State

Kwak

Yoo

Kim

2019

Advanced Optical Materials

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Recently, Rogach's group realized solidstate-luminescent CD/silica composite, which possessed high quantum yield (QY) and PL output with relatively high CD loading (19.2 wt%) by gelation. [18] However, this process was limited to hydroxyl-rich CD only and still suffered from aggregation in extremely high concentration.Fundamental solution is to develop a selfquenching-resistant CD even without dispersion matrices. Polymer CD (PCD), a polymer-like CD consisting of crosslinked matrix and sub-fluorophores, has been studied for solid-state luminescence because crosslinking may prevent π-π interaction. [20][21][22][23] Several groups synthesized quenching-resistant PCD, but those showed red-shifted emission with noticeable color change compared to solutionstate fluorescence. [24][25][26][27] Such spectral shift in solid-state usually occurs with nonradiative decay competitively, which leads to a decrease of QY. In addition, the emission color change in solidstate needs additional optimization process for the fabrication of optoelectronics, so that the energy transfer as an origin for ACQ and red-shift should be strictly avoided.Herein, we synthesized a blue-emitting PCD with the same emission center at 434 nm in both solution-and solid-state through a hydrothermal reaction. By structural and spectroscopic analysis, the origin of solid-state luminescence was investigated. We further identified a reason for the emission color consistency of PCD from dilute solution to powder form by comparing with CD that showed red-shifted emission in solid-state. We also fabricated LED using PCD as a color-converting layer, and it had a luminous efficacy of 12.03 lm W −1 without significant color change even with extremely high loading fraction of 50 wt%. With the increased loading fraction (20 wt%), we enhanced brightness of our LED up to four times compared to the LED fabricated with conventional low loading fraction (0.1-5 wt%) using PCD. Compared to red-shifted CD (RCD)-based LED with the conventional loading fraction, the luminous flux of PCD-based LED with 20 wt% increased by 3 to 15 times. This result would be a great interest to those who study CD-based LED. Results and DiscussionSolid-state luminescent polymer carbon dot (PCD) was synthesized using citric acid (CA) and diethylenetriamine (DETA) through a hydrothermal reaction at 70 °C (Figure 1a). Product Solid-state luminescent carbon dot without dispersion matrices is studied to overcome aggregation-caused quenching, but it usually shows spectral shift between solution-and solid-state accompanying a dramatic decrease of fluorescence intensity, which hinders a real application. Herein, polymer carbon dot (PCD) showing solid-state luminescence without red-shift is synthesized by low-temperature reaction. The PCD solution and solid have the same emission peaks at 434 nm and similar absolute quantum yields of 68.2% and 62.7%, respectively, which is uncommon feature compared to other carbon dots. The mechanism for solid-state luminescence and emission color consistency is invest...

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Supramolecular interactions via hydrogen bonding contributing to citric-acid derived carbon dots with high quantum yield and sensitive photoluminescence

Abstract: Fluorophores coupled with supramolecules lead to “dot” topologies in citric-acid derived carbon dots under the effect of hydrogen bonding.

Cited by 53 publications

References 46 publications

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

A molecular fluorophore in citric acid/ethylenediamine carbon dots identified and quantified by multinuclear solid‐state nuclear magnetic resonance

Quenching‐Resistant Polymer Carbon Dot Preserving Emission Color Consistency in Solid‐State

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