Carbon Dots with Continuously Tunable Full-Color Emission and Their Application in Ratiometric pH Sensing

We present a new strategy of selectively preparing two types of carbon dots with either excitation-independent blue emission or distinctive excitation-dependent full-color emissions from chloroform and diethylamine by varying the reaction conditions

Hui Nie; Minjie Li; Quanshun Li; Shaojun Liang; Yingying Tan; Lan Sheng; Wei Shi; Sean Xiao-An Zhang

2014

Scholarcy highlights

  • Carbon dots represent an important class of photoluminescent nanomaterials due to their attractive properties, including less toxicity, good compatibility, and relatively easy surface modification, etc. Until now, carbon dots have been prepared by a variety of approaches ranging from top-down to bottom-up strategies and have been applied widely in fields of bioimaging, printing inks, photocatalysis, and sensors. Among these works, one of the most studied properties is the excitation-dependent vs the excitation-independent features of emission for C dots. understanding and engineering the unique excitation-dependent emission is very hard, and most of the known C dots have emissions centered in the blue and green regions without using color filters, which is not preferred for biological applications because of the harm of their short wavelength excitation light to living cells or biosystems. It is ideal that the C dots can exhibit continuously adjustable excitation-dependent full-color emission with comparable intensities, because it will realize any visible color by selecting different excitation wavelengths without changing the chemical structure
  • carbon dots have been reported to be prepared from an abundance of resources, such as resols, carbohydrates, citrate acid, and others. Here, by refluxing CHCl3 and DEA for different times, C dots with distinct fluorescent properties can be obtained
  • In the UV–vis spectra, the B-C dots exhibit two shoulder absorption peaks at 228 and 282 nm, which have been observed in a wide range of C dots prepared by other methods. Differently, F-C dots exhibit two shoulder absorption peaks at 300 and 421 nm
  • The detailed emission properties of F-C dots including emission wavelengths at different excitation wavelengths, Δλ, emission intensity, and bandwidth are illustrated in Table S1 in the Supporting Information
  • By a great amount of detailed work, it is found that the surface functional groups of C═O and C═N have efficiently introduced new energy levels for electron transitions and resulted in the continuously adjustable excitation-dependent full-color emissions within a single C dot
  • MTT assays of cell viability studies show greater than 80% cell viability rate for F-C dots with concentrations up to 0.2 mg/mL for 24 h
  • What’s more, the excitation-dependent full-color emission properties of C dots will open the door to a host of new applications, such as a multistates logic gate, by tuning the emission states with a combination of different excitation wavelengths, which is underway in our lab

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