Highly Efficient Fluorescence Quenching of Dye By Defect Rich MoS2

Abstract:

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 MoS_2.  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.