Showing papers by "Vincent M. Rotello published in 1999"

Recognition-Mediated Unfolding of a Self-Assembled Polymeric Globule

Abstract: Diaminotriazine-functionalized polystyrene folds into a highly compact micelle-like structure in nonpolar solvents, as established by gel permeation chromatography. Folding of this polymer arises from intramolecular hydrogen bonding between the triazine moieties, allowing the unfolding process to be effected through competitive intermolecular host−guest interactions. Variable-temperature NMR titrations of this polymer with a complementary host were used to quantify the thermodynamics of this unfolding process.

Control of Polymer Solution Structure via Intra- and Intermolecular Aromatic Stacking

Abstract: Anthracene-functionalized polymer 1 folds into a compact globular structure in nonpolar media. This folding arises from intramolecular aromatic−aromatic interactions of the anthracene side chains. Polymer 1 binds strongly to picric acid (2), through donor−acceptor electrostatic interactions between the electron-rich anthracene side chains and the electron-deficient picric acid guests. This binding stabilizes the thermally labile folded conformation of polymer 1, dramatically altering the temperature dependence of polymer unfolding.

Thermoreversible Polymerization. Formation of Fullerene-Diene Oligomers and Copolymers.

Abstract: Diels−Alder reaction of C60 with bis-anthracene 3 provides linear copolymer 4. This material is stable at room temperature but undergoes reversion to the monomeric species upon heating. This thermal depolymerization process was observed at temperatures above 60 °C, with an activation energy of 17.1 kcal/mol. This process can be cycled multiply without degradation of the reactive functionalities. In addition to its thermal properties, this polymer retains the rich redox chemistry of the fulleroids. Electrochemical and EPR studies demonstrate copolymer 4 undergoes multiple reductions without decomposition to monomeric species.

4-Ethoxycarbonyl-4′,5,5′-trimethyltetrathiafulvalene and its radical cation: Langmuir–Blodgett film studies, EPR spectra and the X-ray crystal structure of (Me3TTF-CO2Et)2·TCNQ complex

Abstract: Langmuir–Blodgett films of the title trimethyltetrathiafulvalene derivative 10 have been assembled without the need for added fatty acid: room temperature, in-plane, dc conductivity values of the films before and after doping with iodine vapour were σrt = 10–5 S cm–1 and 10–1 S cm–1, respectively. Over the temperature range 300–100 K the films exhibited a linear current versus voltage relationship, with an activation energy for conductivity Ea = 0.11 eV. Cyclic voltammetric data were obtained for LB films of 10 and the best response was recorded for a 2-layer film; electroactivity gradually disappeared after a few cycles, which is consistent with film desorption from the electrode. UV–vis and IR spectra of the LB films are consistent with a conjugative intramolecular charge-transfer interaction between the triMe-TTF (donor) and ester (acceptor) moieties of 10 (see structure 10′). This increases the amphiphilic nature of 10 and is believed to play an important role in stabilising the LB film structure. Iodine doping of the LB films leads to the formation of radical cations 10·+, and polarised spectra show that the molecules are aligned at a high angle to the substrate surface. Simultaneous electrochemistry and EPR (SEEPR) studies provide insight into the electronic structure of the radical cation species 10·+ in solution; the ethoxycarbonyl group strongly polarises the spin density, and these data are supported by ab initio UHF and B3LYP calculations. The single crystal X-ray structure of the complex (10)2·TCNQ (TCNQ = tetracyano-p-quinodimethane) reveals a mixed ⋯ADDADD⋯ stacking motif with a low degree of charge transfer between the D and A moieties. Analysis of the bond lengths in the donor moiety confirms a contribution from the zwitterionic structure 10′.