Self-assembly of a C(3v) symmetric trisphenanthroline and linear bisterpyridines in the presence of Cu(+) did not furnish the expected supramolecular nanoprisms in quantitative yield. With an accurately sized tripyridine as a stabilizing template, the nanoprism formed exclusively. Furthermore, an adaptive constriction of the nanoprism was seen with C(60) as template: as a result of the smaller size of C(60) the nanoframework wrapped up around the guest like an accordion-type host system.
A homologous series of three molecules containing thiophene, bithiophene and terthiophene bridges between two redox-active tertiary amino-groups was synthesized and explored. Charge-delocalization in the one-electron oxidized forms of these molecules was investigated by a combination of cyclic voltammetry, near-infrared optical absorption spectroscopy, and EPR spectroscopy. All three cation radicals can be described as organic mixed-valence species, and for all of them the experimental data is consistent with strong delocalization of the unpaired electron. Depending on what model is used for 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 analysis of the optical absorption data, estimates for the electronic coupling matrix element (H AB ) range from ∼5000 cm -1 to ∼7000 cm -1 for the shortest member of the homologous series. According to optical absorption and EPR spectroscopy even the terthiophene radical appears to belong either to Robin-Day class III or to a category of radicals commonly denominated as borderline class II / class III systems. The finding of such a large extent of charge delocalization over up to three adjacent thiophene units is remarkable.
The electronic structures of the radical cations of two dithienylperfluorocyclopentene molecules with appended tertiary amine units were investigated by electrochemical and optical spectroscopic methods. The through-bond N-N distances in the photocyclized (closed) forms of the two systems are 9.3 and 17.6 Å, respectively, depending on whether the nitrogen atoms are attached directly to the two thienyl units or whether xylyl spacers are in between. In the case of the radical cation with the longer N-N distance, photocyclization of the dithienylperfluorocyclopentene core induces a changeover from class I to class II mixed valence behavior. In the case of the shorter system, the experimental data is consistent with assignment of the photocyclized form to a class III mixed valence species.
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