Unusual polymorphism in new bent-shaped liquid crystals based on biphenyl as a central molecular core.

Bent-shaped mesogens possessing a biphenyl as a central core have been synthesized and the role of the terminal chain and the orientation of the ester as a linkage group have been investigated. For the studied molecular core we have established that both parameters play an important role for the mesomorphic properties. The polyfluoroalkyl terminal chain supports the formation of mesophases, and the introduction of a chiral lactate terminal chain destabilizes mesophases for the first type of mutual orientation of ester groups, attached to the central core. On the contrary, for the opposite orientation of esters, the terminal chain has no effect on the mesomorphic properties, and columnar phases have been found for all compounds. A unique phase sequence has been found for the mesogen with the fluorinated chain. A generalized tilted smectics, SmCG, have been observed in a temperature interval between two different lamellar SmCP phases and characterized by X-ray and dielectric measurements. The dielectric spectroscopy data are unique and presented for the first time in the SmCG phase providing new information about the molecular dynamics.

Di- and tri-oxalkyl derivatives of a boron dipyrromethene (BODIPY) rotor dye in lipid bilayers.

The environment-sensitive fluorescent probes provide excellent tools for studying membranes in their native state. We have modified the BODIPY-based fluorescent molecular rotor by increasing the number of alkyl moieties from one to two or three to achieve a more defined and deeper positioning of the probe in membranes. Detailed characterisation of fluorescence properties and localisation/orientation of probes was performed using a variety of fluorescence techniques and model membranes composed of different lipids. As expected, additional alkyls attached to the fluorophore moiety led to a deeper and more defined localisation of the probe in the lipid bilayer. The results strongly indicate that fluorescence properties of such probes are influenced not only by lipid packing but also by the orientation of the probe in membranes. The orientation of rotors studied herein was significantly altered by changes in the lipid composition of membranes. Our observations demonstrate the limits of BODIPY-based molecular rotors as environmental sensors in cellular membranes with complex lipid composition. The results presented herein also underline the importance of the detailed characterisation of fluorescent membrane dyes and provide a guide for future testing.

Synthesis and spectral properties of new fluorescent alkoxy-substituted thieno[3,2-b]indole derivatives.

The synthesis and optical properties of three new fluorescent alkoxy-substituted thieno[3,2-b]indole (TI) derivatives, including 7-methoxy thieno[3,2-b]indole (7-MeOTI), 6,7- methylenedioxythieno[3,2-b]indole (6,7-MDTI) and 6,7-dihexyloxythieno[3,2-b]indole, (6,7-DHTI), were investigated. Electronic absorption spectra, fluorescence excitation and emission spectra, fluorescence quantum yields (ΦF), lifetimes (τF), and other photophysical parameters of the three TI derivatives were measured in DMSO solutions at room temperature. Theoretical electronic absorption and fluorescence spectra were also calculated by means of a molecular orbital (MO) method. For all three alkoxy-TI derivatives, the fluorescence emission maximum wavelength was significantly red shifted relative to un-substituted TI, which was attributed to delocalization of the fused hetero-aromatic ring π electronic system by the electron-donating alkoxy group(s). ΦF values varied from 0.12 to 0.19, according to the compound. τF were short, in the range 0.56-1.13 ns.

Synthesis and electronic properties of D-A-D triads based on 3-alkoxy-4-cyanothiophene and benzothienothiophene blocks.

3-Alkoxy-4-cyanothiophene units are used as building block for the synthesis of conjugated donor-acceptor-donor (D-A-D) triads. The donor part consists of benzothienothiophene end groups associated with the alkoxy groups of the 3-alkoxy-4-cyanothiophene, while the central acceptor part is formed by combining the electron-withdrawing cyano group with thiophene or benzothiadiazole units.

Synthesis, electrochemical, and optical properties of new fluorescent, substituted thieno[3,2-b][1]benzothiophenes.

The synthesis, electrochemical and optical properties of three fluorescent substituted thieno[3,2-b][1]benzothiophenes (TBT) derivatives, including 3-methoxythieno[3,2-b][1]benzothiophene (3-MeO-TBT), 2,3-dimethylthieno[3,2-b][1]benzothiophene (2,3-diMe-TBT), and 6-methoxythieno[3,2-b][1]benzothiophene-2-carboxylate (6-MeO-TBT-2-COOMe), were investigated. The oxidation potential values varied between 1.40 and 1.20 V/SCE according to the electronic substituent effect, and electropolymerization attempts, performed in 0.1 M LiClO(4) acetonitrile solution, led to the formation of very thin films of poly(3-MeO-TBT) and poly(2,3-di-Me-TBT). Electronic absorption spectra, fluorescence excitation and emission spectra, fluorescence quantum yields (Φ(F)) , lifetimes (τ(F)), and other photophysical parameters of the three new TBT derivatives were measured in DMSO solutions at room temperature. For the methyl-and methoxy-substituted TBT derivatives, the fluorescence emission peak were slightly red shifted relative to that of unsubstituted TBT (Δλ(em) = 1-12 nm) whereas, in the case of 6-MeO-TBT-2-COOMe, a rather strong red-shift (Δλ(em) = 73 nm) was attributed to the existence of a "push-pull" electronic interaction of the MeO and COOMe groups. All Φ(F) values were rather high, varying between 0.11 and 0.35, according to the substituent effect. Fluorescence decays were mono-exponential and τ(F) values were very short, ranging between 0.11 and 0.30 ns for the substituted TBT derivatives until study.