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Abstract Recently, doping guest materials such as quantum dots (QDs) into liquid crystals (LCs) has been of great interest since their addition substantially enhances the properties of LC and opens new avenues for scientific advancement. Here, we report the induction of homeotropic alignment in cells without alignment layers of the negative dielectric nematic liquid crystal, N-(4-Methoxybenzylidene)-4-butylaniline (MBBA) by doping with carbon dots (CDs ∼2.8 ± 0.72 nm). The CDs-MBBA composites (CDs concentration: 0.002, 0.01, 0.03, 0.1 and 0.3 wt%) were investigated using optical polarising microscopy, electro-optical and dielectric techniques. Polarizing optical micrographs and voltage dependent optical transmission revealed the induced homeotropic alignment for all the composites under investigation. Interestingly, the least concentrated sample, 0.002 wt% exhibited partial homeotropic alignment. However, due to light leakage, the optical transmission value below threshold voltage was relatively higher than the rest of the composites. MBBA is a negative dielectric material, hence the application of a voltage across the cell was able to switch the alignment from a dark to a bright state for all composites. However, above a certain voltage (>threshold voltage), the bright state produced some instabilities. The value of dielectric permittivity was observed to decrease with increasing concentration, confirming the effect of CDs in producing homeotropic alignment in MBBA. Measurements as a function of temperature were conducted to examine the thermal stability of the induced alignment. The alignment was found to be stable throughout the nematic phase of MBBA. The induction of such alignment without conventional alignment (i.e., rubbing of polyimides) technique can be helpful in addressing the evolving display demands by making liquid crystal displays (LCDs) and other display devices cost effective. 

ree bis(4-oligoethyleneoxyphenyl) viologen bistosylate salts of different lengths were prepared via the Zincke reaction followed by a metathesis reaction with silver tosylate, and their chemical structures confirmed by 1H, 13C nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) techniques, and elemental analysis. Thermogravimetric analysis (TGA) showed these salts had excellent thermal stabilities, losing just 5 % of their initial mass between 283 and 288 °C. Liquid crystalline phases and transition temperatures were determined by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and variable temperature X-ray diffraction (VTXRD) techniques. The salts exhibited weak fluorescent emission in dichloromethane and no emission in acetonitrile but exhibited light emission in the solid state. Their absolute quantum yields ranged between 3 and 12 %. Impedance spectroscopy showed that the ionic conductivity of the salts increases with the number of oxyethylene units in the extended viologen moiety. The salt-containing four oxyethylene units at each end reach a conductivity value of 10-2 S·cm−1, attributed to its larger molecular flexibility and improved ionic liquid mobility.