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Study of Compression-Induced Supramolecular Nanostructures of an Imidazole Derivative by Langmuir–Blodgett Technique

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journal contribution
posted on 09.08.2017 by Bapi Dey, Pintu Debnath, Santanu Chakraborty, Barnali Deb, Debajyoti Bhattacharjee, Swapan Majumdar, Syed Arshad Hussain
In this communication, we report the design and synthesis as well as the supramolecular assembly behavior of a 2,4,5-triaryl imidazole derivative (compound 1) at the air–water interface and in thin films using Langmuir–Blodgett (LB) technique. The main idea for such a chemical structure is that the long alkyl chain and N–H of the imidazole core may help to form supramolecular architecture through the hydrophobic–hydrophobic interaction and hydrogen bonding, respectively. Accordingly, the interfacial behavior as well as morphology of 1 in thin films were studied through a series of characterization methods such as surface pressure–area (π–A) isotherm, hysteresis analysis, ultraviolet–visible (UV–vis) absorption and steady-state fluorescence spectroscopies, Fourier transform infrared, X-ray diffraction, Brewster angle microscopy (BAM), and atomic force microscopy (AFM) measurements, and so forth. Pressure–area isotherm is an indication toward the formation of supramolecular nanostructures instead of an ideal monolayer at the air–water interface. This has been confirmed by the hysteresis analysis and BAM measurement at the air–water interface. AFM images of 1 in the LB monolayer exhibits the formation of supramolecular nanowires as well as nanorods. By controlling different film-forming parameters, it becomes possible to manipulate these nanostructures. With the passage of time, the nanowires come close to each other and become straight. Similarly, nanorods come close to each other and form bundles of several rods in the LB films. H-bonding, J-aggregation, as well as compression during film formation might play a key role in the formation of such nanostructures. Electrical switching behavior of compound 1 was also observed because of the presence of an electron donor–acceptor system in 1. This type of organic switching behavior may be promising for next-generation organic electronics.