Abstract
The superior optical properties of Silicon Quantum Dots (SQDs) have made them of increasing interest for a variety of biological and opto-electronic applications. The surface functionalization of the SQDs with aromatic ligands plays a key role in controlling their optical properties due to the interaction of the ligands with the electronic wave function of SQDs. However, there is limited reports in literature describing the impact of spacer groups connecting the aromatic chromophore to SQDs on the optical properties of the SQDs. Herein, we report the synthesis of two SQDs assemblies (1.6 nm average diameter) functionalized with perylene-3,4,9,10-tetracarboxylic acid diimide (PDI) chromophore through N-propylurea and propylamine spacers. Depending on the nature of the spacer, the photophysical measurements provide clear evidence for efficient energy and/or electron transfer between the SQDs and PDI. Energy transfer was confirmed to be the operative process when propylurea spacer was used, in which the rate was estimated to be ~2 × 109 s−1. On the other hand, the propylamine spacer was found to facilitate electron transfer process within the SQDs assembly. To illustrate functionality, the water soluble SQD-N-propylurea-PDI assembly was proven to be nontoxic and efficient for fluorescent imaging of embryonic kidney HEK293 cells and human bone cancerous U2OS cells.
Highlights
The size-tuneable PL of Silicon Quantum Dots (SQDs) is assigned to the quantum confinement effect where the PL is blue-shifted when the size of SQDs is more than ~3 nm
It should be noted that the low resolution of the TEM and HR-TEM images is assigned to the ultra-small dimensions of these SQDs and the small atomic weight of the silicon atom compared to the counterpart metallic or semiconductor quantum dots, which is known to provide low-quality visualization[10,24]
Using simple and environmentally friendly chemistry, we were able to synthesize two dyad systems coupling the SQDs of an average size of ~1.6 nm with perylene-3,4,9,10-tetracarboxylic acid diimide (PDI) chromophore through N-propylurea or propylamine spacers
Summary
The size-tuneable PL of SQDs is assigned to the quantum confinement effect where the PL is blue-shifted when the size of SQDs is more than ~3 nm. The surface functionalization would play a crucial role towards controlling the optical properties of SQDs9 It has been shown in previous studies that surface functionalization of SQDs with aromatic ligands helps tune their optical properties including their quantum yield and PL10,11. This strategy potentially can be utilized as a means to control the optical properties of SQDs. the functionalization of SQDs with organic ligands increases their stability towards oxidation and prevents them from agglomeration and aggregation[12]. The products Am-SQD-Per and Urea-SQD-Per were characterized using high-resolution transmission electronic microscopy (HRTEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis absorption spectroscopy, and steady-state and times-resolved emission spectroscopy
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