Stratton Brandy-Fey C, Pierre Angelina J, Riser Elizabeth A, Grinalds Nathan J, Edwards Charles W, Wohlwend Anna M, Bauer Jacob S, Spera Rachel J, Pferdmenges Lauren S, Griffith Kaitlyn M, Hunter Brandon W, Bobadova-Parvanova Petia, Day Cynthia S, Lundin Pamela M, Fogarty Keir H
Department of Chemistry, High Point University, High Point, North Carolina 27268, United States.
Department of Chemistry and Fermentation Sciences, Appalachian State University, Boone, North Carolina 28608, United States.
J Phys Chem A. 2022 Jul 7;126(26):4211-4220. doi: 10.1021/acs.jpca.2c02665. Epub 2022 Jun 24.
Amide derivatives of xanthene dyes such as rhodamine B are useful in a variety of sensing applications due to their colorimetric responses to stimuli such as acidity changes and UV light. The optical properties of these molecules can be influenced by intermolecular associations into dimeric structures, but the exact impact can be hard to predict. We have designed a covalently linked intramolecular dimer of the dye rhodamine B utilizing -phenylenediamine to link the two dyes via amide bonds. The doubly closed spirolactam version of this dimer, , is isolated as a colorless solid. Under acidic conditions or UV exposure, solutions develop a pink color that is expected for the ring-opened form of the molecule. However, nuclear magnetic resonance (NMR) and single-crystal diffraction data show that the equilibrium still prefers the closed dimer state. Interestingly, the emission profile of shows solvatochromic blue fluorescence. Control studies of model compounds with similar structural motifs do not display similar blue fluorescence, indicating that this optical behavior is unique to the dimeric form. This behavior may lend itself to applications of such xanthene dimers to more sophisticated sensors beyond those with traditional binary on/off fluorescence profiles.
