(170a) SMART Solar Transmittance Modulation in Newly Engineered Organic Molecules with Multistimulated Optical Switchability and Reversibility

Modern buildings consume considerable amount of energy for cooling and ~37% of this energy is basically from solar heat gain while heat losses through windows comprise over 40% of the total building energy leakages. This lead to the integration of advanced solar control devices onto modern energy saving buildings to provide optimized utilization and control of radiant solar energy. Hence, the development of “smart curtains” or smart windows. Conventionally, these smart windows are electrochromic (EC) devices comprised of multiple layers of functional materials stacked over each other and are sandwiched between two transparent conductive electrodes such as indium tin oxide (ITO). Electron trapping resulting from interface blocking at different functional layers, however, limits the performance of the device and the multiple layer configuration increases fabrication complexity. Furthermore, this type of devices absorbs only specific wavelength in the solar spectrum allowing the rest of the spectral wavelength get pass the EC device permitting undesirable solar heat gain. It led our group develop new class of organic molecules and present an alternative approach to effectively control incoming solar light. By integrating alkylated viologens onto newly engineered azolium-based poly(ionic liquid)s via quaternization reaction, new molecules exhibiting multiple functions were obtained. Utilizing these new engineered molecules warrants the design transition of these smart devices from a classic multilayered configuration to an “all-in-one” configuration. Owing to the viologen’s ability to undergo reduction-oxidation when triggered electrically, the molecules produce colored states which can be tuned depending on the molecular make-up. Autonomously, the presence of N-isopropylacrylamide in the molecular structure let the material undergo phase transition from a clear state to a translucent-opaque state when stimulated thermally above its lower critical solution temperature (LCST). Dual stimulation of the molecules permits a truly black optical state. Remarkably, the synergistic effect of the molecules’ thermochromism and electrochromism when activated concurrently shows full absorption of the entire visible solar spectrum. Modifying the alkyl substituent, oxyethylene spacer length, counteranion and water content, allows tunability of the molecules’ overall performance in terms of the optical contrast, switching kinetics, coloration efficiency and cyclic stability for more efficient solar transmittance modulation in smart windows.