Self-Assembly and Polymerization of Perylene Diimide-Diacetylene Conjugates

Abstract

Because of their unique structural and optical properties, perylene diimide (PDI) derivatives have gained great attention for use in optoelectronic devices. However, PDI containing self-assembled supramolecular systems often have limited use because of the weak force of noncovalent interaction assisted molecular association during the assembly process such as hydrogen bonding, π-π stacking and hydrophobic interactions. As a result, they are intrinsically unstable under solution processing conditions. To overcome this limitation, we have developed a polydiacetylene (PDA) based structural strategy to construct a solvent-resistant and stable PDI assembly. For this purpose, we first generated the monomer PDI-BisDA, in which two polymerizable diacetylene (DA) units are covalently linked to a PDI core. Importantly, 254 nm UV irradiation of self-assembled PDI-BisDA nanofibers forms solvent-resistant and stable PDI-PDA fibers. Owing to the presence of PDA, the generated polymer fibers display increased conductivity. In addition, the existence of PDA and PDI moieties in the fiber leads to the occurrence of switchable on-off FRET between the PDI and reversibly thermochromic PDA chromophores. We also reported a polydiacetylene based strategy to achieve a highly sensitive trimethylamine (TEA) sensor. A strategy of UV-induced polymerization under continuous heating (to 130 oC) was adopted to trap and preserve the molecular orientation of the post-crystal-crystal phase transition by virtue of a robust PDA backbone. Analyzing the molecular–packing–performance relationship revealed a dramatic enhancement of TEA vapor detection response due to crystal-crystal transition in PDI-PDA solid. Self-assembly is a dynamic process that often takes place through a stepwise pathway involving the formation of kinetically favored metastable intermediates prior to the generation of a thermodynamically preferred supramolecular framework. Although trapping intermediates in these pathways can provide significant information about both their nature and the overall self-assembly process, it is an extremely challenging venture without altering temperature, concentrations, chemical compositions and morphologies. In the second part of the study, we reported a strategy of controlled molecular packing of the material through UV-induced polymerization under continuous heating. In the next part of this dissertation, we have described a highly efficient and potentially feasible method for “trapping” metastable intermediates in self-assembly processes based on a photopolymerization strategy and its application. By employing an asymmetric structure of chiral perylene-diimide (PDI) possessing a diacetylene (DA) chain, we demonstrated that the metastable intermediates including nanoribbons, nanocoils and nanohelices can be effectively trapped by using UV promoted polymerization before they form thermodynamic tubular structures. The strategy developed in this study should be applicable to a naturally and synthetically abundant alkyl chain containing self-assembling systems.