Photoswitchable Rhodamine‐Based Multianalyte Sensors for Metal Ion Detection

Abstract

We have developed three azobenzene‐core‐based molecular systems decorated with different numbers of rhodamine units as photoswitchable multianalyte sensors. Exploiting the ring‐opening of the spirolactam part of the rhodamine unit, the resulting fluorescence response, and modulation of it through the photoswitching of azobenzene by light, we utilized them in the detection of multiple metal ions (Fe3+, Fe2+, Sn2+ and Al3+). The binding sites, stoichiometry, binding constants, fluorescent lifetimes and limit of detection (LOD) for each probe have been deduced using appropriate spectroscopic techniques. The limit of detection (LOD) of 5 a, 5 b and 5 c for Fe3+ are found to be 4.2×10−7±7.8×10−9 M, 2.2×10−7±4.6×10−9 M and 1.2×10−7±4.6×10−9 M, respectively. The fluorescence response of the metal‐chelated complex can be manipulated effectively by employing the photoswitching ability of azobenzene that makes them useful as chemosensors for various individual metal ions.

Recent Advances in Photoswitchable Fluorescent and Colorimetric Probes

“…By utilizing various ligands combined with diarylethene, the Pu group has also developed additional photoswitchable fluorescent probes for detecting Hg 2+ [154], Cd 2+ [155][156][157], Cr 3+ [158], and Sn 2+ [159]. Through meticulous molecular design, combining photo-responsive azobenzene moieties with other reactive fluorescent groups, it is possible to develop photoswitchable fluorescent probes for detecting metal ions [160,161]. Raman et al have successfully synthesized a novel molecular dyad that cleverly integrates fluorescent rhodamine with photochromic azobenzene, connected via a phenylene bridge (Figure 10) [160].…”

“…Additionally, further light exposure to the 1-Fe 3+ complex did not induce azobenzene isomerization but did result in an increased absorption at 556 nm, suggesting the formation of more open-ring amide forms of rhodamine. This observed behavior is believed to be due to energy transfer from the photoexcited azobenzene to the rhodamine, Through meticulous molecular design, combining photo-responsive azobenzene moieties with other reactive fluorescent groups, it is possible to develop photoswitchable fluorescent probes for detecting metal ions [160,161]. Raman et al have successfully synthesized a novel molecular dyad that cleverly integrates fluorescent rhodamine with photochromic azobenzene, connected via a phenylene bridge (Figure 10) [160].…”

“…Through meticulous molecular design, combining photo-responsive azobenzene moieties with other reactive fluorescent groups, it is possible to develop photoswitchable fluorescent probes for detecting metal ions [ 160 , 161 ]. Raman et al have successfully synthesized a novel molecular dyad that cleverly integrates fluorescent rhodamine with photochromic azobenzene, connected via a phenylene bridge ( Figure 10 ) [ 160 ].…”