Abstract
The development of fluorescent sensors for Hg2+ has attracted much attention due to the well-known adverse effects of mercury on biological health. In the present work, the optical properties of two newly-synthesized Hg2+ chemosensors based on the coumarin-rhodamine system (named Pro1 and Pro2) were systematically investigated using time-dependent density functional theory. It is shown that Pro1 and Pro2 are effective ratiometric fluorescent Hg2+ probes, which recognize Hg2+ by Förster resonance energy transfer and through bond energy transfer mechanisms, respectively. To further understand the mechanisms of the two probes, we have developed an approach to predict the energy transfer rate between the donor and acceptor. Using this approach, it can be inferred that Pro1 has a six times higher energy transfer rate than Pro2. Thus the influence of spacer group between the donor and acceptor on the sensing performance of the probe is demonstrated. Specifically, two-photon absorption properties of these two probes are calculated. We have found that both probes show significant two-photon responses in the near-infrared light region. However, only the maximum two-photon absorption cross section of Pro1 is greatly enhanced with the presence of Hg2+, indicating that Pro1 can act as a potential two-photon excited fluorescent probe for Hg2+. The theoretical investigations would be helpful to build a relationship between the structure and the optical properties of the probes, providing information on the design of efficient two-photon fluorescent sensors that can be used for biological imaging of Hg2+ in vivo.
Highlights
Mercury is a caustic and carcinogenic element with high cellular toxicity which can pass through biological membranes and cause serious damage to the neurological and endocrine systems [1,2,3], which makes the detection of mercuric ion (Hg2+ ) of great importance in the fields of biology, chemistry and medicine [4,5,6]
One-photon absorption and emission strength between the states i and j can be described by the oscillator strength: 2ωij x,y,z δOPA(OPE) =
The photoabsorption and photoemission properties, recognition mechanisms and energy transfer rates of two newly-synthesized fluorescent Hg2+ chemosensors were studied by theoretical calculations
Summary
Mercury is a caustic and carcinogenic element with high cellular toxicity which can pass through biological membranes and cause serious damage to the neurological and endocrine systems [1,2,3], which makes the detection of mercuric ion (Hg2+ ) of great importance in the fields of biology, chemistry and medicine [4,5,6]. The design of effective fluorescent probes has become a focus of attention in fluorescence microscopy [9,10,11]. Several recognition mechanisms have been employed in probe design [4,12,13]. Srivastava et al synthesized a fluorescent probe by bridging a benzhydryl moiety and a dansyl fluorophore through a piperazine unit to detect Hg2+ [14]. Razi et al designed a fluorescence turn-on ratiometic probe for Hg2+ by bridging imidazole and benzothiazole moieties through a thiophene ring [15]. Even though much success has been achieved in the development of ICT-based fluorescent probes, the shortage of alternatives is evident. It is widely accepted that the detection using ICT-based fluorescent probes depends highly on the intensity of the single characteristic fluorescent band, which
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