title: Reversible chemistry of CO2 in the preparation of fluorescent supramolecular polymers.
abstract: The chemistry between CO(2) and primary amines was used to construct novel types of supramolecular polymers and networks. Fluorescent self-assembling gel 2 was prepared, which employs both hydrogen bonding and dynamic, thermally reversible carbamate bonds. As precursors, biscalixarenes 1, 3, 4, 6, and 7 were synthesized, which strongly aggregate (K(D) > or = 10(6) M(-1) per capsule) in apolar solution with the formation of linear self-assembling polymers. Polymer 1n possesses CO(2)-philic primary amino groups on the periphery. CO(2) rapidly reacts with chains 1n in apolar solvents and cross-links them with the formation of multiple carbamate salt bridges. Three-dimensional polymeric network 2 was characterized by (13)C NMR spectroscopy and SEM. Addition of competitive solvent breaks hydrogen bonding in 2 but does not influence the carbamate linkers. Carbamate salt 9 was obtained. On the other hand, thermal release of CO(2) from 2 and 9 was easily accomplished (1 h, 100 degrees C) with retaining the hydrogen-bonding capsules. Thus, three-dimensional polymeric networks 2 were transformed back to linear polymeric chains 1n without their breakup. Multiple pyrene fluorophores, attached on the periphery of 2, cause strong fluorescence of the gel with benzene. When approximately 5% nitrobenzene was gelated together with benzene, fluorescence strongly decreases due to the energy transfer from the pyrene donors in gel 2 to trapped nitrobenzene molecules. This opens a way to switchable fluorescent materials.
authors.affiliation: Department of Chemistry & Biochemistry, University of Texas at Arlington, Arlington, TX 76019-0065, USA.
authors.forename: Heng
authors.initials: H
authors.lastname: Xu
authors.forename: Dmitry M
authors.initials: DM
authors.lastname: Rudkevich
mesh_terms: D000588:Amines / Q000737:chemistry; D047250:Calixarenes / Q000138:chemical synthesis* / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D005453:Fluorescence; D005782:Gels / Q000138:chemical synthesis; D006860:Hydrogen Bonding; D046911:Macromolecular Substances; D008968:Molecular Conformation; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000588:Amines; D005782:Gels; D046911:Macromolecular Substances; D011108:Polymers; D047250:Calixarenes; D002245:Carbon Dioxide