480367 Highly Efficient Fluorescence Quenching of Dye By Defect Rich MoS2
Highly efficient fluorescence quenching of dye by defect rich MoS2
Bradley Miller, Swagotom Sarkar, Hongmei Luo, Sanchari Chowdhury
Fluorescence quenching of dye molecules near MoS2 can be used as a probe to investigate the nature of electron or energy transfer between any fluorescent molecules and MoS2. The efficiency of defect rich (DR) and defect free (DF) few-layer MoS2 in terms of quenching were tested using two different dye molecules, with different molecular structures and absorption/emission profiles, a red fluorescent dye 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) and a green fluorescent dye, fluorescein sodium salt, both of which, were in an aqueous solution. The optical absorption spectrum of DF MoS2 exhibits multiple discrete absorption bands as expected from their band structure. However, for DR MoS2 there were not any observable distinct strong absorbance peaks in the wavelength range of 300nm to 900nm. A simple assay that measures the quenching efficiency of these MoS2 on fluorescent dyes was used when both are mixed together in solution at different concentrations. Under these conditions, steady-state measurements revealed that the quenching efficiency of DF MoS2 is higher for fluorescein dye, emitting near the strongest absorption peak of MoS2 around 400 nm. The quenching effects due to DF MoS2 are dynamic in nature, as the fluorescence can be recovered by separating out DF MoS2 from solution.
Most interestingly, the quenching efficiency of DR MoS2 was significantly higher than DF MoS2 for fluorescein. However, DR samples show no discrete absorption features near the emission wavelength of the fluorescein dye. The fluorescence quenching properties of DR MoS2 are, therefore, found to be distinct from few-layer MoS2. It was hypothesized that since defects, such as vacancies, are active centers for molecular adsorption, it may be forming ground state complexes with the dye molecules. The second reason, may be, that hindered electron mobility in DR MoS2 increases dielectric loss in DR MoS2, hence this could increase the fluorescence quenching effect. Further experiments are underway to confirm the hypothesis.
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