Engineering of Stilbazolium/iodocuprate Hybrids with Photo/electrical Performances by Modulating Inter-molecular Charge Transfers among H-Aggregated Chromophores
Combination of D-π-A stilbazolium-type chromophores bearing ortho-N-alkyl substituents with iodocuprate result in three new hybrids, i.e., [(CMAMP)2(CuI3)(Acetone)0.5]n (1), [(HMAMP)(Cu3I4)]n (2), [(HMAHP)2(Cu5I7)]n (3), which present natural quantum-well architectures with void spaces of quasi-2-D organic layers occupied by iodocuprate anions via C-H•••I hydrogen bonds. D-π-A stilbazolium dyes exhibit head-to-tail arranged H-aggregations with face-to-face π•••π stacking interactions. Theoretical calculations suggest that the charge densities on benzenes can be strengthened from electron-withdrawing group (–CN) to electron-donating group (–OH), and the –C2H5OH substituents on ortho-N of pyridines not only help to open the band gaps but also provide steric effect for better face-to-face π•••π stacking interactions. Therefore, HMAHP+ in 3 possesses the strongest face-to-face π•••π stacking interactions due to presence of longer –C2H5OH group on ortho-N position, consequently, blue-shift photoluminescence, stronger photocurrent (0.28 mA), higher ON/OFF ratio (1.6×104) can be observed in 3. Specially, electrical bistability performances can be observed on ITO/hybrids/PMMA/Ag devices, which are explained as Schottky emission, SCLC and Ohmic mechanisms. According to theoretical calculation, the band gaps switching from semi-conductor to conductor (HRS to LRS) after trapping electrons are exclusively dominated by π bonding and anti-bonding orbitals of stilbazolium dyes, which points out the direction for the design of stilbazolium-containing memory devices.