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

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.