Poly(Pyridinium Salt)s Containing 2,7-Diamino-9,9'-Dioctylfluorene Moieties with Various Organic Counterions Exhibiting Both Lyotropic Liquid-Crystalline and Light-Emitting Properties.

A series of poly(pyridinium salt)s-fluorene main-chain ionic polymers with various organic counterions were synthesized by using ring-transmutation polymerization and metathesis reactions. Their chemical structures were characterized by Fourier Transform Infrared (FTIR), proton (1H), and fluorine 19 (19F) nuclear magnetic resonance (NMR) spectrometers. These polymers showed a number-average molecular weight (Mns) between 96.5 and 107.8 kg/mol and polydispersity index (PDI) in the range of 1.12-1.88. They exhibited fully-grown lyotropic phases in polar protic and aprotic solvents at different critical concentrations. Small-angle X-ray scattering for one polymer example indicates lyotropic structure formation for 60-80% solvent fraction. A lyotropic smectic phase contains 10 nm polymer platelets connected by tie molecules. The structure also incorporates a square packing motif within platelets. Thermal properties of polymers were affected by the size of counterions as determined by differential scanning calorimetry and thermogravimetric analysis measurements. Their ultraviolet-visible (UV-Vis) absorption spectra in different organic solvents were essentially identical, indicating that the closely spaced π-π* transitions occurred in their conjugated polymer structures. In contrast, the emission spectra of polymers exhibited a positive solvatochromism on changing the polarity of solvents. They emitted green lights in both polar and nonpolar organic solvents and showed blue light in the film-states, but their λem peaks were dependent on the size of the counterions. They formed aggregates in polar aprotic and protic solvents with the addition of water (v/v, 0-90%), and their λem peaks were blue shifted.

Thermotropic Liquid-Crystalline and Light-Emitting Properties of Bis(4-aalkoxyphenyl) Viologen Bis(triflimide) Salts.

A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide in methanol. Their chemical structures were characterized by 1H and 13C nuclear magnetic resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry, polarizing optical microscopy, and variable temperature X-ray diffraction. Salts with short length alkoxy chains had crystal-to-liquid transitions. Salts of intermediate length alkoxy chains showed both crystal-to-smectic A (SmA) transitions, Tms, and SmA-to-isotropic transitions, Tis. Those with longer length of alkoxy chains had relatively low Tms at which they formed the SmA phases that persisted up to the decomposition at high temperatures. As expected, all of them had excellent thermal stabilities in the temperature range of 330-370 °C. Their light-emitting properties in methanol were also included.

Synthesis, Optical Spectroscopy, and Laser and Biomedical Imaging Application Potential of 2,4,6-Triphenylpyrylium Tetrachloroferrate and Its Derivatives.

Synthesis, optical spectroscopic properties, two-photon (TP) absorption-induced fluorescence, and laser and bioimaging application potentials of 2,4,6-triphenylpyrylium tetrachloroferrate (1),4-(4-methoxyphenyl)-2,6-diphenylpyrylium tetrachloroferrate (2), 2,6-bis(4-methoxyphenyl)-4-phenylpyrylium tetrachloroferrate (3), and 2,4,6-tris(4-methoxyphenyl)pyrylium tetrachloroferrate (4) are presented. The synthesis involves the conversion of pyrylium tosylates to pyrylium chlorides, followed by transformation into 1-4 on heating to reflux with FeCl3 in acetonitrile. They are characterized using 1H and 13C NMR spectra in CD3OD, and FTIR and Raman spectroscopic techniques. The salts dissolve in organic solvents and water (pH = 7 to 3) even at high concentrations (10-3 M). These solutions absorb light strongly from 500-300 nm. Solutions of 1, 3, and 4 fluoresce with high quantum yield in the 500-700 nm spectral range. Salts 1 and 4 exhibit fluorescence lifetime shortening, line width narrowing, and free-running laser action under intense pulsed laser excitation. Toxicity and cell imaging studies using human cancer cell lines reveal that salts 1 and 3 function as cellular fluorophores in vitro and have no adverse effects on cellular viability at nanomolar ranges. Furthermore, acetonitrile and methanol solutions of salts 1, 3, and 4 exhibit strong two-photon absorption-induced fluorescence, opening potential applications in biomedical imaging and microscopy.