title: Squaraine-derived rotaxanes: sterically protected fluorescent near-IR dyes.
abstract: A squaraine dye with bulky end groups is employed as the thread component in two Leigh-type amide rotaxanes. The rotaxanes are synthesized in a simple two-step process. X-ray crystal structures of the rotaxanes show that the pyridyl-containing macrocycle is more rigid and wraps more tightly around the cyclobutene core of the squaraine thread compared to the isophthalamide-containing macrocycle. The rotaxanes exhibit photophysical properties that are similar to the precursor squaraine. The encapsulating macrocycle greatly increases the chemical stability of the squaraine thread and inhibits aggregation-induced broadening of its absorption spectrum. It should be possible to prepare squaraine-derived rotaxanes with improved properties for a wide range of photophysical, photochemical, and biomedical applications.
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: Easwaran
authors.initials: E
authors.lastname: Arunkumar
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Forbes
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Noll
authors.forename: Bradley D
authors.initials: BD
authors.lastname: Smith
mesh_terms: D018360:Crystallography, X-Ray; D003503:Cyclobutanes / Q000737:chemistry*; D003505:Cyclodextrins / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry*; D010777:Photochemistry; D043862:Rotaxanes / Q000737:chemistry*; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
chemical_list: D003503:Cyclobutanes; D003505:Cyclodextrins; D005456:Fluorescent Dyes; D010636:Phenols; D043862:Rotaxanes; C480596:squaraine