The Nanoarchitectonics of Sustainable Smart Window Design by LCST Modulation of Photoresponsive Molecular π-Systems

Lower Critical Solution Temperature (LCST) of macromolecular systems is important in thermoresponsive smart window design. However, controlling the LCST behavior and sustaining the shelf-life are challenging tasks. Herein, how photochemistry can be tweaked to design sustainable smart windows that allow controlled transmission of solar radiation is described. The cyanostilbene substituted naphthalenes 1(Z) and 2(Z), show Z/E-photoisomerization and subsequent Mallory cyclization resulting in significant modulation in clouding temperatures (Tcloud). At 1 mM concentration, the Tcloud of 1(Z), and 1(E) are 33 +/- 0.1 and 28 +/- 0.13 degrees C, respectively whereas 2(Z) and 2(E) exhibit Tcloud around 37 +/- 0.1 and 30 +/- 0.1 degrees C, respectively. The high thermal barrier for the E/Z back isomerization of 1(E) and 2(E) and removal of oxygen from the reaction medium allow control of the photoprocesses, thereby facilitating the construction of sustainable smart windows that respond to the surrounding temperature. A 30 x 30 cm2 window prototype containing an aqueous solution of 1(Z) (1 mM) exhibits a fully transmissive state at 25 degrees C and a nearly zero-transmissive state at 33 degrees C for 10,000 cycles of operation. It is demonstrated that Z/E-photoisomerization and Mallory photocyclization in cyanostilbene derivatives 1(Z) and 2(Z) can be tweaked to construct sustainable smart windows that regulate the transmittance of solar radiation through glass panels. Prototype windows constructed with 1(Z) are found operate at an ideal cloud temperature of 28 degrees C suitable for tropical climate for 10,000 cycles without any loss of performance. image