Sunday, 26 May 2019

Fast electrically switchable anisotropic photoluminescence

P. Lakshmi Madhuri, D.S. Shankar Rao, C. V. Yelamaggad and A.S. Achalkumar, and S. Krishna Prasad, Adv. Opt. Mater., 3, 1116 (2015)

Reversibly photoluminescent (PL) switchable materials are important in several fields such as ultrahigh-density optical data storage, molecular switches and wires, optoelectronic devices, sensors, organic light emitting diodes, genetic probes. A wide variety of luminescent polymers and organic materials have been developed to cater to these needs. However, deployment of these materials for practical applications suffers principally from drawbacks such as low contrast (ON/OFF intensity ratio), irreversibility or slow response. Although the intrinsic anisotropy of liquid crystalline PL materials can address the contrast problem, the associated dynamics is slow, being in the range of seconds. We prepared composites of the host dual frequency response liquid crystal material and a PL disc-like molecule. A two-frequency protocol utilized to drive the PL composite between two anisotropic states brings about a dramatic acceleration in the dynamics yielding two-orders of magnitude faster responses while enhancing the fluorescence contrast as well. The protocol has built-in adaptability in terms of the magnitude and frequency of the field to get intermediate values of the contrast, creating a “grey scale”. The finding is attractive from the viewpoint of fast fluorescence imaging, detection of action potentials in neurons and photoluminescent displays.

Posted by S. Krishna Prasad