Multimodal Stimuli-Responsive Poly(2-isopropyl-2-oxazoline) with Dual Molecular Logic Gate Operations

Azobenzene end-functionalized telechelic POx (Az-POx-Az) was designed for as multimodal stimuli-responsive polymer. Az-POx-Az (0.25 g/L) in physiological saline (150 mM NaCl) phosphate buffered solution (10 mM PBS, pH 7.4) exhibited fully reversible trans-cis photoisomerism upon alternate irradiation with 365 and 254 nm UV light. The photoisomerization of the azobenzene moieties influenced the lower critical solution temperature (LCST), and the cis form exhibited a slightly higher LCST than the trans form. Circular dichroism measurements of Az-POx-Az with cyclodextrins (CDs) exhibited induced circular dichroism at the absorption band of the azobenzene moiety, indicating the formation of host-guest complexes between the azobenzene moieties in Az-POx-Az and the CDs. After formation of host-guest complexes consisting of the azobenzene moieties and the CDs, Az-POx-Az exhibited increased LCSTs. Interestingly, the LCSTs of Az-POx-Az with α-CD and β-CD moved in opposite directions upon photoisomerization. By the changing from the trans to cis form, Az-POx-Az with α-CD exhibited a decreased LCST; however, Az-POx-Az with β-CD exhibited an increased LCST. Using the interconversions between the transparent and turbid states of the Az-POx-Az solution, we could realize two different logic circuit modes using three different external stimuli, i.e., temperature, UV light, and cyclodextrins.