Dual photoluminescence and charge transport in an alkoxy biphenyl benzoate ferroelectric liquid crystalline–graphene oxide composite

Abstract

An optimized concentration of graphene oxide (GO) has been dispersed in a ferroelectric liquid crystalline (FLC) material namely 4′-(octyloxy)-[1,1′-biphenyl]-4-yl 4-(heptan-2-yloxy)benzoate, to prepare a FLC–GO composite. Temperature dependent photoluminescence (PL) measurements for the FLC–GO composite were conducted between 30–100 °C. We observed a superlinear increase in the PL with increasing temperature. The time resolved luminescence study exhibits a bi-exponential decay time with a shorter life time for the FLC–GO composite and confirms the surface energy transfer from GO to FLC. Charge transport and current–voltage (I–V) characteristics for the FLC–GO composite have been investigated at ambient conditions by using current sensing atomic force microscopy. For the FLC–GO composite, critical diode like nonlinear I–V curves have been obtained in which the charge transport is assigned to the thermally active intermolecular hopping at room temperature. The FLC material yields ionic charge mobilities of 1.45 × 10⁻⁵, 1.26 × 10⁻⁵ and 9.83 × 10⁻⁶ cm² V⁻¹ s⁻¹ in isotropic, chiral nematic (N*) and chiral smectic C (SmC*) phases. The dispersion of GO significantly enhances the ionic mobility in the composite which was observed to be 2.71 × 10⁻⁴, 2.69 × 10⁻⁴ and 2.65 × 10⁻⁴ cm² V⁻¹ s⁻¹ for the aforementioned phase sequence. Physical interactions between GO and FLC molecules were confirmed by FTIR and polarized optical microscopy. In-plane coupling between the orientation of GO and the long molecular axis of the FLC molecules remarkably enhances the band intensity of CO, C–H, COO, C–O and C–H vibrations. The size of multi-domain fan texture in the SmC* phase has been enhanced after the dispersion of GO. The cobweb like networking in the oily streaks texture of the N* phase confirms the interesting molecular architecture via planar anchoring between FLC molecules and GO. This work opens new avenues towards applications in pico-ampere current-regulated electronic devices and opto-electronics.