Trifluoromethyl-substituted conjugated oligoelectrolytes.
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.
Ren
Yan
Y
Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, California 93106, USA.
Bazan
Guillermo C
GC