Thermochromic Fluorophores 2018–2021
The inherent limitations of current thermosensitive dyes motivated Professor Raymo to design thermochromic compounds capable of interconverting spontaneously between two spectrally-resolved emissive states with the ultimate goal of developing a general strategy to probe temperature on the basis of ratiometric fluorescence measurements. Indeed, methods to probe temperature with fluorescence measurements avoid altogether the need of physical contact, essential in conventional thermometry, to enable the determination of this crucial physical parameter noninvasively at the molecular level. However, most thermosensitive fluorescent probes are based on the temperature dependence of a single emission band and suffer from concentration effects and optical artifacts. These complications can be overcome if a second spectrally-resolved emission band is engineered into the thermosensitive system to provide a built-in internal reference.
In search of appropriate structural designs for thermosensitive dual emission, Professor Raymo envisaged the possibility of replacing the oxazine heterocycle of his original photochromic compounds with an oxazole ring. In aqueous environments, the resulting molecular switches equilibrate with fast kinetics between two species with resolved fluorescence (a), as a consequence of the opening and closing of the oxazole heterocycle. On the basis of these unprecedented design principles, his research group developed a family of thermochromic fluorescent switches with support from the National Aeronautics and Space Administration. These studies demonstrated that the two equilibrating compounds can be imaged simultaneously in separate detection channels (b) and that the ratio of their emission intensities varies monotonically with temperature. As a result of this unique behavior, temperature distributions could be mapped in aqueous solutions and hydrogel matrices with spatial resolution at the micrometer level. This protocol for the quantification of temperature at the microscale can evolve into a general method for noninvasive thermometric measurements in a diversity of samples that would otherwise be impossible with conventional thermometers and current thermosensitive fluorophores.
- “Exploring the Ability of Thermo-Fluorescent Dyes to Probe the Near Surface Ocean Structure”: National Aeronautics and Space Administration, 80NSSC18K0774 (PI: P. J. Minnett, Co-PI: F. M. Raymo), $ 346,357, 05/01/18–04/30/21
- “Ratiometric Temperature Sensing with Fluorescent Thermochromic Switches”: M. M. A. Mazza, F. Cardano, J. Cusido, J. D. Baker, S. Giordani, F. M. Raymo, Chem. Commun., 2019, 55, 1112−1115
- “Fluorescence Switching for Temperature Sensing in Water”: Y. Zheng, Y. Meana, M. M. A. Mazza, J. D. Baker, P. J. Minnett, F. M. Raymo, J. Am. Chem. Soc., 2022, 144, 4759–4763
- “Structural Designs for Ratiometric Temperature Sensing with Organic Fluorophores “: M. M. A. Mazza, F. M. Raymo, J. Mater. Chem. C, 2019, 7, 5333–5342