Fluorescent Molecular Rotors Based on Hinged Anthracene Carboxyimides

Abstract

Temperature and viscosity are essential parameters in medicine, environmental science, smart materials, and biology. However, few fluorescent sensor publications mention the direct relationship between temperature and viscosity. Three anthracene carboxyimide-based fluorescent molecular rotors, 1DiAC∙Cl, 2DiAC∙Cl, and 9DiAC∙Cl, were designed and synthesized. Their photophysical properties were studied in various solvents, such as N, N-dimethylacetamide, N, N-dimethylformamide, 1-propanol, ethanol, dimethyl sulfoxide, methanol, and water. Solvent polarizability resulted in a solvatochromism effect for all three rotors and their absorption and emission spectra were analyzed via the Lippert–Mataga equation and multilinear analysis using Kamlet–Taft and Catalán parameters. The rotors exhibited red-shifted absorption and emission bands in solution on account of differences in their torsion angle. The three rotors demonstrated strong fluorescence in a high-viscosity environment due to restricted intramolecular rotation. Investigations carried out under varying ratios of water to glycerol were explored to probe the viscosity-based changes in their optical properties. A good linear correlation between the logarithms of fluorescence intensity and solution viscosity for two rotors, namely 2DiAC∙Cl and 9DiAC∙Cl, was observed as the percentage of glycerol increased. Excellent exponential regression between the viscosity-related temperature and emission intensity was observed for all three investigated rotors.

Rational Design of Near-Infrared Fluorescent Probes for Accurately Tracking Lysosomal Viscosity with Allyl Snchoring Si-Rhodamine

“…To solve these issues, it was found that the nonradiative decay of the excited state of the fluorescent molecular rotors can be changed by the environmental viscosity, which has become a new method to determine the microviscosity changes in a biological environment. 22,23 Additionally, fluorescence imaging was wellknown for high spatiotemporal resolution, invasiveness, and sensitivity. 24−26 Especially, the near-infrared (NIR) region (>650 nm) fluorescent dyes with large Stokes shifts have better penetration depth and antibackground interference ability and therefore are widely applied in biomedical analysis and diagnosis caused by changes in the microenvironment.…”

“…Because of the limitations of detection methods, there are few studies on viscosity as an important marker of microenvironments in biological processes and disease diagnosis. To solve these issues, it was found that the nonradiative decay of the excited state of the fluorescent molecular rotors can be changed by the environmental viscosity, which has become a new method to determine the microviscosity changes in a biological environment. , Additionally, fluorescence imaging was well-known for high spatiotemporal resolution, invasiveness, and sensitivity. − Especially, the near-infrared (NIR) region (>650 nm) fluorescent dyes with large Stokes shifts have better penetration depth and antibackground interference ability and therefore are widely applied in biomedical analysis and diagnosis caused by changes in the microenvironment. − Up to now, the rotors and fluorophores of most viscosity-responsive probes were connected with double bonds or single bonds . In a low-viscosity environment, the probe releases weak fluorescence resulting from the free rotation of rotor-connected single or double bonds, while as viscosity increases their rotation was inhibited by forming a large conjugated system, and result in strong fluorescence in a tall-viscosity environment. , Interestingly, most rhodamine and other fluorophores-based viscosity probes, their rotors are composed of aromatic ring: benzo-indole, polyaniline group, benzo-thiophene, pyridine salt, quinoline, imidazole, azobenzene, etc.…”