New molecular materials combining ionic and electronic functions have been prepared by using liquid crystals consisting of terthiophene-based mesogens and terminal imidazolium groups. These liquid crystals show thermotropic smectic A phases. Nanosegregation of the pi-conjugated mesogens and the ionic imidazolium moieties leads to the formation of layered liquid-crystalline (LC) structures consisting of 2D alternating pathways for electronic charges and ionic species. These nanostructured materials act as efficient electrochromic redox systems that exhibit coupled electrochemical reduction and oxidation in the ordered bulk states. For example, compound 1 having the terthienylphenylcyanoethylene mesogen and the imidazolium triflate moiety forms the smectic LC nanostructure. Distinct reversible electrochromic responses are observed for compound 1 without additional electrolyte solution on the application of double-potential steps between 0 and 2.5 V in the smectic A phase at 160 degrees C. In contrast, compound 2 having a tetrafluorophenylterthiophene moiety and compound 3 having a phenylterthiophene moiety exhibit irreversible cathodic reduction and reversible anodic oxidation in the smectic A phases. The use of poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate) (PEDOT-PSS) as an electron-accepting layer on the cathode leads to the distinct electrochromic responses for 2 and 3. These results show that new self-organized molecular redox systems can be built by nanosegregated pi-conjugated liquid crystals containing imidazolium moieties with and without electroactive thin layers on the electrodes.

A new electrochromic molecule comprised of pi-conjugated and ionic moieties has been designed and synthesized. It forms a nanosegregated smectic phase in which ion-conductive layers of imidazolium salts are located between hole transport layers of phenylterthiophene moieties. Electrochromism is observed in the bulk liquid crystal state of this compound without an electrolyte solution. In this nanosegregated smectic phase, an electrical double layer is formed rapidly at the electrode. Consequently holes are injected from the electrode, resulting in oxidation of the pi-conjugated moieties.

Liquid-crystalline (LC) behavior and ionic conductivities of imidazolium salts containing an L-glutamic acid moiety have been studied. The ionic conductivities of the (CF 3 SO 2 ) 2 N À salt forming the columnar LC phase are higher than those of the Br À salt in the columnar LC state. The ionic conductivity shows a sudden decrease at the columnar-micellar cubic LC transition of the Br À salt.Self-assembly of liquid-crystalline (LC) molecules with functional moieties is one of the versatile approaches to the preparation of functional soft materials with dynamic and anisotropic nature.1-4 Ionic liquid crystals 5-8 have attracted attention because they have potentials for applications as ion conductors, 6 redox-active materials, 7 and ordered solvents. 8 They form a variety of LC nanostructures 1,2,9 such as micelles, cylinders, layers, and bicontinuous cubic structures through ionic interactions and nanosegregation between ionic and non-ionic moieties.Recently, we have reported on one-dimensional ion conduction in ionic columnar liquid crystals, 6a-6d 1-methyl-3-[3,4,5-tris(alkyloxy)benzyl]imidazolium salts containing BF 4 À , PF 6 À , CF 3 SO 3 À , and (CF 3 SO 2 ) 2 N À (TFSI À ). The LC properties and ionic conductivities were strongly dependent on the properties of counter anions. To obtain highly ion-conductive materials, the use of TFSI À is considered to be desirable because of its negative charge delocalization and weak electrostatic interactions with cations.10 However, the preparation of LC imidazolium TFSI À salts that form columnar phases in wide temperature ranges has not yet been achieved. 6a-6c For the preparation of self-assembled materials that exhibit stable mesophases, it should be important to control intermolecular interactions and the balance of volume fraction of ionic and non-ionic parts of the molecules. 2,9,11 Our molecular design here is to attach a fan-shaped L-glutamic acid derivative bearing bis(alkyloxy)phenyl moieties 12 to imidazolium salts (Figure 1). The glutamic acid derivative can be used as a molecular building block to produce stable columnar and micellar cubic LC materials upon hydrogen bonding.12 In addition, the incorporation of a more bulky lipophilic part than those of previously reported ionic molecules 6a-6c into imidazolium salts may induce a structural change from columnar to micellar cubic phases, leading to the on-off switch 3d of ion conduction (Figure 2). Herein, we report on self-assembly of imidazolium-based ionic liquid crystals 1 and 2 exhibiting stable columnar and cubic LC phases and their ionic conductivities.The LC properties of 1 and 2 are summarized in Table 1. Compound 1 exhibits columnar and cubic phases, while compound 2 shows only a columnar phase in the temperature range that is wider than those of previously reported imidazoliumbased LC salts with TFSI À . 6b The X-ray diffraction (XRD) patterns confirm that the LC phases of 1 and 2 at 80 C are hexagonal columnar phases. The intercolumnar distances for both of 1 and 2 are 50 Å . The XRD pattern o...

The authors present white polymer light-emitting electrochemical cells (PLECs) fabricated with polymer blend films of poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and π-conjugated triphenylamine molecules. The PLECs have bulk heterojunction structures composed of van der Waals interfaces between the PFD segments and the amine molecules. White-light electroluminescence (EL) can be achieved via light-mixing of the blue exciton emission from PFD and long-wavelength exciplex emission from excited complexes consisting of PFD segments (acceptors (As)) and the amine molecules (donors (Ds)). Precise control of the distances between the PFD and the amine molecules, affected through proper choice of the concentrations of PFD, amine molecules, and polymeric solid electrolytes, is critical to realizing white emission. White PLECs can be fabricated with PFD and amine molecules whose highest occupied molecular orbital (HOMO) levels range from −5.3 eV to −5.0 eV. Meanwhile, PLECs fabricated with amine molecules whose HOMO levels are lower than −5.6 eV cannot produce exciplex emission. The distances between the PFD and amine molecules of the exciplexes appear to be larger than 0.4 nm. These experimental data are explained by perturbation theory using the charge-transfer state (A−D+), the locally excited state (A*D), which is assumed to be the locally excited acceptor state in which there is no interaction with the donor molecule; and the energy gap between the HOMO levels of the PFD and the amine molecules. Color-stable white PLECs were fabricated using 4,4′,4″-tris[N-(2-naphthyl)-N-phenylamino]-triphenylamine, which has a HOMO level of −5.2 eV, as the amine molecule, and the color stability of the device is a function of the fact that PFD forms exciplexes with these molecules.