Effect of Functional Group on Electrical Switching Behaviour of an Imidazole Derivative in Langmuir‐Blodgett Film

Abstract

Here we report the design and synthesis of an imidazole derivative namely 1-benzyl-2,4,5-triaryl imidazole (compound 2) and its switching behaviour assembled onto Langmuir-Blodgett (LB) films. Monolayer characteristic of compound 2 at the air-water interface has been studied by surface pressure vs area per molecule (π -A) isotherm, hysteresis analysis and insitu Brewster Angle Microscopy (BAM). These studies indicated the formation of stable floating Langmuir film at the water subphase. Atomic Force Microscopy (AFM) investigation confirmed the successful deposition of the Langmuir film onto solid substrate. Device consisted of 60 layers LB films of 2 showed resistive bipolar switching behaviour irrespective of the first applied bias voltage polarity. Observed bipolar switch-ing has been explained in terms of reduction -oxidation process. Due to the presence of strong reducible group (C = N) in the imidazole core, reduction -oxidation process takes place easily during bias. Presence of sharp reduction and oxidation peaks in the Cyclic Voltammetry (CV) measurement of 2 also supported this hypothesis. Presence of benzyl group with the imidazole core played the crucial rule in the reductionoxidation process and hence the switching behaviour. When benzyl group was replaced by a '-H' then bipolar switching was not observed. In that case oxidizable group N -H opposed the reduction process during bias. This type of bipolar switching is very promising for future technological applications in organic electronics.

Resistive Switching of the Tetraindolyl Derivative in Ultrathin Films: A Potential Candidate for Nonvolatile Memory Applications

“…To have an idea of the orientation of Indole1 molecule in the Langmuir film in the solid phase, we have analyzed the cross-sectional area of the molecule and compared the same with the mean molecular area. 22 Assuming the Indole1 molecule to be a cuboid box having three sides with lengths of 1.412, 0.904, and 0.5 nm, we calculate the three cross-sectional areas to be 0.452, 0.706, and 1.276 nm 2 (Figure S3 in the Supporting Information). A close look at these values suggests that the mean molecular area (area per molecule for the solid phase) is very close to 0.452 nm 2 (i.e., the cross-sectional area corresponds to the vertical orientation of the molecule).…”

“…This also suggests that the Indole1 molecule forms a one-molecule-thick packed monolayer film at the air−water interface at higher surface pressure. 22 Also, we have calculated the compressibility of the floating film within the 5−15 and 25−35 mN/m surface pressure regions following the procedure described elsewhere. 32 It has been observed that the compressibility value in the higher surface pressure region (29.85 mN −1 ) is lower than that in the lower surface pressure region (40.42 mN −1 ).…”

“…This intern switches the device to its ON state via electroreduction. 22 Thus, conjugation within the molecules is extended, resulting in a lowering of the HOMO−LUMO energy gap. 22 This leads the device to its highly conducting (low resistance) ON state.…”

“…22 Thus, conjugation within the molecules is extended, resulting in a lowering of the HOMO−LUMO energy gap. 22 This leads the device to its highly conducting (low resistance) ON state. The observed electroreduction of Indole1 molecules may involve two possibilities: (i) injection of the electron when it overcomes the difference in energy between the LUMO level of the molecule and the work function of the ITO electrode and (ii) transport of the electron via applied-bias-dependent hopping.…”

Resistive switching behaviour of organic molecules

“…It has been observed that imidazole derivative (2,4,5-triaryl imidazole) formed nanostructures when organized onto LB films and showed resistive switching behavior due to charge transfer between the donor−acceptor groups present in the molecule [52]. On the other hand imidazole derivative 1-benzyl-2,4,5-triaryl imidazole showed bipolar switching behavior, where, reduction -oxidation process played crucial rule for the observed bipolar switching [53]. These kind of bipolar switching of organic molecule is very important for memory application and logic element in integrated circuit.…”