title: Trifluoromethyl-substituted conjugated oligoelectrolytes.
abstract: Conjugated oligoelectrolytes (COEs) are being introduced into a variety of optical and electronic technologies, yet the dependence of their properties as a function of molecular structure remains poorly understood. In response, we designed, synthesized, and examined a new tetracationic COE, namely, 1,4-bis{9',9'-bis[6''-(N,N,N-trimethylammonium)hexyl]-2'-fluorenyl}-2,5-bis(trifluoromethyl)benzene tetrabromide (FPF-F6), which contains bulky electron-withdrawing trifluoromethyl groups, and compared its properties with the unsubstituted counterpart 1,4-bis{9',9'-bis[6''-(N,N,N-trimethylammonium)hexyl]-2'-fluorenyl}benzene tetrabromide (FPF). The ground-state geometry of FPF-F6 is primarily twisted with little electronic communication between the aromatic units, as confirmed by single-crystal X-ray diffraction studies of the neutral precursor. However, absorption and photoluminescence spectroscopies reveal that the excited state of FPF-F6 displays strong intramolecular charge-transfer characteristics. Solution AFM in aqueous media shows that introduction of trifluoromethyl groups changes the size and aspect ratio of supramolecular aggregates that are brought together as a result of hydrophobic interactions. Furthermore, addition of ssDNA to FPF-F6 leads to interoligoelectrolyte complexes wherein the backbone is more planar; the environment the chromophore experiences under these conditions is also considerably less polar. These findings provide considerable insight into the complex photophysics of electronically conjugated materials in aqueous media.
authors: Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, California 93106, USA.
authors: Yan
authors: Y
authors: Ren
authors: Guillermo C
authors: GC
authors: Bazan