S2(A) Synthesis and photophysical data for the intermediates and sensitizers: General: 1 H NMR Spectra were recorded with a Varian INOVA 400NMR instrument.MS data were obtained with GCT CA156 (UK) high resolution mass spectrometer (HRMS) or HP1100 LC/MSD (USA) mass spectrometer. UV-vis spectra of the dyes in solutions were recorded in a quartz cell with 1 cm path length on a HP 8453 spectraphotometer. Melting-points were measured with a X-4 melting-point apparatus with microscope.The several of π-conjugating spacers 5a-8a were prepared using known procedures. 5a and 6a were prepared by Suzuki coupling of 2-thienylboronic acid with corresponding 2-bromothiophene and 2,5-dibromothiophene, respectively. 7a was obtained in 3 steps from 3-bromothiophene according to the already reported procedures. [1,2] 8a of E-configuration was prepared by McMurry coupling of 2-thiophenecarboxaldehyde. [3] 2,2,4-Trimethyl-1,2-dihydro-quinoline(1a)To a solution of aniline (18.7 g, 0.2 mol) and toluenesulfonic acid (1.9 g) in cyclohexane (20 mL), acetone (42 mL, 0.57 mol) was added dropwise at 80~90 ºC for 8~10 h. The resulted water was removed by co-boiling with cyclohexane. Sodium carbonate (0.55 g) in water (20 mL) was poured into the reaction mixture after complete addition of acetone at 70 ºC. The reaction mixture was stirred overnight at r.t. The organic layer was washed with water and dried over magnesium sulfate. The unreacted acetone and solvent was romoved by rotary evaporation. The residue was distilled in vacuo to give 1a as colorless oil (130 ºC/10 mmHg, 17 g, 49%). 1 H NMR
The desired control of size, structure, and optical properties of fluorescent carbon dots (CDs) is critical for understanding the fluorescence mechanism and exploring their potential application. Herein, a top-down strategy to chemically tailor the inexpensive coal to fluorescent CDs by a combined method of carbonization and acidic oxidation etching is reported. The size and optical properties of the as-made CDs are tuned by controlling the structures of graphitic crystallites in the starting precursor. The coal-derived CDs exhibit two different distinctive emission modes, where the intensity of the short-wavelength emission is significantly enhanced by partial reduction treatment. The evolution of the electronic structure and the surface states analysis show that two different types of fluorescence centers, nano-sized sp(2) carbon domains and surface defects, are responsible for the observed emission characteristics. The reduced CDs are demonstrated as an effective fluorescent sensing material for label-free and selective detection of Cu(II) ions with a detection limit as low as 2.0 nM, showing a great promise for real-world sensor applications.
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