Solvent-Type Passivation Strategy Controls Solid-State Self-Quenching-Resistant Behavior in Sulfur Dots

Abstract

Treatment of sulfur dots with polyethylene glycol (PEG) has been an efficient way to achieve a high luminescence quantum yield, and such a PEG-related quantum dot (QD)-synthesis strategy has been well documented. However, the polymeric insulating capping layer acting as the “thick shell” will significantly slow down the electron-transfer efficiency and severely hamper its practical application in an optoelectric field. Especially, the employment of synthetic polymers with long alkyl chains or large molecular weights may lead to structural complexity or even unexpected changes of physical characteristics for QDs. Therefore, in sulfur dot preparation, it is a breakthrough to use short-chain molecular species to replace PEG for better control and reproducibility. In this article, a solvent-type passivation (STP) strategy has been reported, and no PEG or any other capping agent is required. The main role of the solvent, ethanol, is to directly react with NaOH, and the generated sodium ethoxide passivates the surface defects. The afforded STP-enhanced emission sulfur dots (STPEE-SDs) possess not only the self-quenching-resistant feature in the solid state but also the extension of fluorescence band toward the wavelength as long as 645 nm. The realization of sulfur dot emission in the deep-red region with a decent yield (8.7%) has never been reported. Moreover, a super large Stokes shift (300 nm, λex = 345 nm, λem = 645 nm) and a much longer decay lifetime (109 μs) have been found, and such values can facilitate to suppress the negative influence from background signals. Density functional theory demonstrates that the surface passivation via sodium ethoxide is dynamically favorable, and the spectroscopic insights into emission behavior could be derived from the passivation effect of the sulfur vacancy as well as the charge-transfer process dominated by the highly electronegative ethoxide layer.

Efficient Mechanochemical Conversion of Elemental Sulfur to Circularly Polarized Luminescent Sulfur Quantum Dots

“…Further, we performed electron paramagnetic spectroscopic (EPR) experiments on a powder l -Sdots sample and recorded the spectrum to know the existence of defects at room temperature. The EPR spectrum shows a broad signal located at g = 2.1 and indicates the sulfur vacancies in l -Sdots (Figure b) . The defect species is designated by vacancy sites or dangling bonds on the edge state of the sulfur core. − Additionally, the EPR spectrum of sulfur was recorded as a control (Figure S5).…”

“…The EPR spectrum shows a broad signal located at g = 2.1 and indicates the sulfur vacancies in L-Sdots (Figure 2b). 31 The defect species is designated by vacancy sites or dangling bonds on the edge state of the sulfur core. 32−35 Additionally, the EPR spectrum of sulfur was recorded as a control (Figure S5).…”

Shaping Sulfur Precursors to Low Dimensional (0D, 1D and 2D) Sulfur Nanomaterials: Synthesis, Characterization, Mechanism, Functionalization, and Applications

“…The performance of SQDs depends largely on their surface functionalization or composition which are influenced by different capping agent (e.g., PVA, Hep, CMC, HP-β-CD, PSS etc). [59,60,[92][93][94]105] For instance, by using poly (4-styrene sodium sulfonate) (PSS) as a capping agent, Wang et al designed a negatively charged SQDs (PSS-SQDs). The negatively charged PSS covers the surface of SQDs and prevents SQDs from aggregation due to strong electrostatic repulsion (Figure 21a).…”

“…The performance of SQDs depends largely on their surface functionalization or composition which are influenced by different capping agent (e.g., PVA, Hep, CMC, HP‐β‐CD, PSS etc). [ 59,60,92–94,105 ] For instance, by using poly (4‐styrene sodium sulfonate) (PSS) as a capping agent, Wang et al. designed a negatively charged SQDs (PSS‐SQDs).…”

Rapid and scalable synthesis of sulfur quantum dots through ozone etching: photoluminescence and FRET-mediated Co2+ sensing

“…However, some efforts have been made to shorten the reaction time through novel methods such as hydrothermal treatment, [28][29][30] an ethylenediamine-assisted acceleration strategy, 31 ethylenediamine-assisted solvothermal treatment, 32 and a solvent-type passivation strategy. 33 Meanwhile, ultrasoundmicrowave-assisted etching, 34 a dielectric barrier discharge-accelerated H 2 O 2 etching strategy, 35 and mechanical grinding assisted synthesis 36 have drastically reduced the reaction time to almost 2 h. Such progress in the synthesis strategies has not only deepened our understanding regarding the growth dynamics and photophysical properties of SQDs but also expanded their scope in various applications, including fluorescent polymer composites, 32 sensing 26,37,38 two-photon fluorescence imaging, 27 anticounterfeiting 36 and food packaging. 39 Nonetheless, the rapid and facile synthesis of highly luminescent SQDs from elemental sulfur continues to be challenging.…”