Photochemical reaction, acidichromism, and supramolecular nanoarchitectures in the Langmuir-Blodgett films of an amphiphilic styrylquinoxaline derivative.

An amphiphilic styrylquinoxaline derivative, 3-(4-(hexadecyloxy)styryl)quinoxalin-2(1H)-one (SQC16), was newly synthesized to investigate their photochemical and gas responsive properties in organized molecular films. It was observed that SQC16 can spread as a monolayer on the subphases with various pH values and be subsequently transferred onto solid substrates. While SQC16 showed predominantly reversible trans-cis photoisomerization in methanol solution, it showed both photoisomerization and photodimerization in Langmuir-Blodgett (LB) films. Photodimerization was only observed in the LB film due to the face-to-face arrangement of the functional headgroup in the LB film, and the process was irreversible. In addition, the LB film showed acidichromism, i.e., when the film was exposed to HCl gas its color changed from yellow to red, and the color could be recovered after exposure to NH(3) gas. The process was reversible and could be repeated many times. An interesting surface morphology of the SQC16 LB film was revealed. It was observed that SQC16 can form nanowire architecture in the transferred one-layer LB film. This morphology can be changed upon photoirradiation or in gas reactions. Through the atomic force microscopy measurements it was suggested that the photodimerization predominantly occurred from the nanowire structures, while during the acidichromism the reaction occurred preferentially in the flat region. X-ray diffraction studies revealed that while layer distance showed a slight change for the LB film during acidichromism and photoreaction, the layer structure of SQC16 LB film was retained.