Design, synthesis and functionalization of organic and metal-containing [pi]-conjugated push-pull chromophores : from photophysics to organic electronic application studies

Abstract

Fully beta- and meso-substituted free base porpyhrins and metalloporphyrins have been successfully synthesized and characterized. Different types of substituents with various electronic nature have been successfully introduced onto the beta- and meso-positions of the porphyrin core. One of the metalloporphyrins has been structurally determined by X-ray crystallography, revealing a ruffling conformation. The photophysical, electrochemical and thermal properties of this series of porphyrins were studied in detail. Some of the target zinc(II) porphyrin complexes were found to be emissive in solution state with emission bands in the near-infrared region. The potential application of utilizing metalloporphyrins as active materials in organic resistive memory have been explored. Devices based on a nickel(II) porphyrin with push and pull beta-substituents were found to exhibit ternary resistive memory behavior while binary memory behavior was observed for devices prepared from push only and pull only counterparts.

A new class of axial- and peripheral-substituted boron subphthalocyanines has been designed and synthesized. Attachments of various donor-acceptor types of substituents on axial and peripheral positions have been achieved to modulate their molecular properties intrinsically. Their photophysical and electrochemical properties were found to be sensitive to the position of the functionalization. Axially-substituted boron subphthalocyanines were found to show efficient energy transfer from the boron subphthalocyanine core to the axial substituents. Distinct excited-state photophysical properties were observed for selected axial- and peripheral-substituted boron subphthalocyanines by using nanosecond and femtosecond transient absorption spectrocopy. While characterisic triplet-triplet transient absorptions of the boron subphthalocyanine core were shown by axially-substituted target compounds in the nanosecond time regime, peripherally substituted boron subphthalocyanines were found to show solvent-dependent photo-induced electron transfer from the peripheral substituents on the boron subphthalocyanine core in the femtosecond time range. In the examination of resistive memory properties, devices prepared from an axially-substituted derivative were found to exhibit multistate memory property while binary memory devices were obtained from a peripherally-substituted derivative.

Other than nature-inspired macrocyclic compounds, a new class of donor-acceptor bis-enediyne-containing pi-conjugated organic small molecules has been prepared and characterized. Their photophysical, electrochemical and thermal properties were examined. The excited state properties of this class of compound were investigated by femtosecond transient absorption spectrocopy. Selected representatives showed positive transient absorption signals at ca. 650 nm, which were tentatively assigned as the formation of cation radicals of the conjugated bis-enediyne backbones. The potential application of this class of compounds as donor materials in solution processable bulk-heterojunction solar cells has been explored by serving as co-donors with poly(3 hexylthiophene). By using [6,6]-phenyl-C61-butyric acid methyl ester as electron acceptor, a power conversion efficiency of up to 2.63 % was achieved by doping 10 wt % of a derivative into poly(3 hexylthiophene). In addition to the optoelectronic properties, the exploration of the resistive memory behavior on selected derivatives has also been attempted. Binary logic was observed for devices based on these derivatives.