Effect of CsPbBr3 perovskite quantum dots on molecular alignment, dielectric and memory effect of a cyanobiphenyl based liquid crystal

• Published in: Journal of molecular liquids 2024-12, Vol.416, p.126480, Article 126480
• Main Authors: Meena, Harikesh, Varshney, Depanshu, Mal, Santanu, Prakash, Jai, Castagna, Riccardo, Singh, Gautam
• Format: Article
• Language: English
• Subjects: Composites; Dielectric spectroscopy; Liquid crystal; Memory effect; Perovskite quantum dots; Polarising optical microscopy
• ISSN: 0167-7322
• DOI: 10.1016/j.molliq.2024.126480

•Dielectric parameters of 8CB, LC are significantly tuned by dopant CsPbBr3 PQDs.•Tuning of memory effect in SmA phase of 8CB, LC by varying concentration of dopant CsPbBr3 PQDs.•Complete memory effect in SmA phase of 1.0 wt% CsPbBr3 PQDs doped 8CB composite. We demonstrate here the impact of doping of CsPbBr3 perovskite quantum dots (CsPbBr3 PQDs, diameter ∼ 7–9 nm) on the molecular alignment, dielectric and memory effect of nematic (N) and smectic A (SmA) phases of a thermotropic liquid crystal material, namely 4-octyl-4′-cyanobiphenyl (8CB) using polarising optical microscope and dielectric spectroscopy. There is no significant change in the alignment of N and SmA phases of 8CB by the doping of CsPbBr3 PQDs, except the color change attributed to the tuned birefringence of 8CB by PQDs. The slight aggregation of PQDs is observed in both LC phases of 1.0 wt% CsPbBr3 PQDs-8CB composite and which could be due to the higher dopant concentration in 8CB matrix. The dielectric parameters (permittivity, loss and anisotropy) of N and SmA phases of 8CB are found to be strongly dependent on the dopant concentration. The dielectric anisotropy (Δε′) of 8CB is observed to decrease with increase in the dopant concentration except 0.5 wt% composite. The temperature dependent Δε′ further confirms that there is no significant change in the clearing temperature of composites as compared to pure 8CB. The short axis molecular relaxation observed in both N and SmA phases of pure 8CB and its composites on the application of 40 V bias. The slight spectral shift of this relaxation towards lower frequency side and decrease in the amplitude of ɛ″ in both SmA and N phases of 1.0 wt% composite as compared to the pure 8CB and composites with concentration lower than 1.0 wt%. The partial memory effect is observed in SmA phase of pure 8CB through voltage-dependent dielectric permittivity and cross-polarised optical textures. The observed memory effect in SmA phase is found to improve with increase in the concentration of PQDs. Most importantly, the complete memory effect is observed in SmA phase of 1.0 wt% CsPbBr3 PQDs-8CB composite. This could be attributed to the holding of smectic layers reorientation achieved at 40 V bias for longer duration after the removal of 40 V bias voltage. A point to be noted here is that no memory effect is observed in the N phase of pure 8CB and its composites with CsPbBr3 PQDs. Our results on CsPbBr3 PQDs-8CB composites are clearly indicative towards thei