The engineering of stilbazolium/iodocuprate hybrids with optical/electrical performances by modulating inter-molecular charge transfer among H-aggregated chromophores

摘要

The combination of D-pi-A stilbazolium-type chromophores bearing ortho-N-alkyl substituents with iodocuprate resulted in three novel hybrids, these were, [(CMAMP)(2)(CuI3)(acetone)(0.5)](n) (1), [(HMAMP)(Cu3I4)](n) (2), and [(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-HMIDLINE HORIZONTAL ELLIPSISI hydrogen bonds. The D-pi-A stilbazolium dyes exhibit head-to-tail arranged H-aggregations with face-to-face pi MIDLINE HORIZONTAL ELLIPSIS pi stacking interactions. Theoretical calculations suggest that the charge densities on the benzenes can be strengthened from the electron-withdrawing group (-CN) to the electron-donating group (-OH), and the -C2H5OH substituents on the ortho-N of the pyridines not only help to open up the band gaps, but also provide a steric effect for better face-to-face pi MIDLINE HORIZONTAL ELLIPSIS pi stacking interactions. Therefore, HMAHP(+) in 3 possesses the strongest face-to-face pi MIDLINE HORIZONTAL ELLIPSIS pi stacking interactions owing to the presence of a longer -C2H5OH group in the ortho-N position, and consequently, blue-shifted photoluminescence, a stronger photocurrent (0.28 mA), and a higher ON/OFF ratio (1.6 x 10(4)) can be observed in 3. In particular, electrical bistability performances can be observed in ITO/hybrids/poly (methyl methacrylate) (PMMA)/Ag devices, which are explained using Schottky emission, space-charge-limited current effect (SCLC) and Ohmic mechanisms. According to theoretical calculations, the band gap switching from the semi-conductor to the conductor (high resistance state (HRS) to low resistance state (LRS)) after trapping electrons is exclusively dominated by the pi bonding and anti-bonding orbitals of the stilbazolium dyes, which indicates a future direction for the design of stilbazolium-containing memory devices.