Toward polymerized artificial photosystems with supramolecular n/p-heterojunctions and antiparallel redox gradients

Abstract

The evaluation of the importance of both ordered and oriented supramolecular architectures for artificial photosynthesis is a topic of current scientific concern. The objective of this study was to synthesize polymerizable zipper architectures and determine the impact of zipper polymerization on the performance of artificial photosystems. We report the synthesis of negatively and positively charged red naphthalenediimides that are equipped with short and long alkenyl tails and attached along oligophenylethynyl scaffolds. The presence of the short butenyl tails turns out to be tolerated by zipper assembly, whereas those of the longer undecenyl tails are not acceptable. Polymerization of the short-tailed zippers with olefin metathesis, using different catalysts in different solvents, is consistently found to reduce the photocurrent generation. These results suggest that polymerization indeed takes places but disturbs rather than stabilizes supramolecular zipper architectures, i.e., that supramolecular systems perform better than macromolecular architectures, at least in the context of this study. We conclude that constructive covalent capture of artificial photosystems should occur during and not after the self-organization of the artificial photosystems. This important conclusion calls for the invention of self-organizing polymer brushes for the synthesis of advanced organic photosystems

Modular Assembly of Poly(naphthalene diimide) and Ru(II) Dyes for an Efficient Light-Induced Charge Separation in Hierarchically Controlled Polymer Architectures

“…Polymers based on naphthalene diimide (NDI) are intensively investigated as n-type semiconductors. The NDI unit exhibits reversible reduction steps, which are as well as the optical and physical properties tunable by different substituents on the molecular scaffold. − Additionally, their sizable planar π-system is capable for self-organization, e.g., a face-to-face stacking of the units. − Main-chain conjugated NDI polymers are typically prepared by polycondensation and reach high charge charier mobilities, , whereas side-chain decorated polymers are conveniently prepared by controlled radical polymerization procedures . Ruthenium polypyridyl complexes are widely used photosensitizer due to their metal-to-ligand charge transfer (MLCT) character of the excited state. − In addition to the ubiquitous [Ru­(bpy) 3 ] 2+ complexes (bpy is 2,2′-bipyridine), e.g.…”

Stack Exchange Strategies for the Synthesis of Covalent Double-Channel Photosystems by Self-Organizing Surface-Initiated Polymerization

“…Available approaches to build directly on the surface, such as layer-by-layer assembly, give little axial and no lateral organization . The alternative zipper assembly has been successful in building supramolecular n/p-heterojunctions with oriented double-channel gradients, but the synthetic efforts involved are much too demanding for general use, and covalent capture studies have failed . Classical polymer brushes seem to stop growing as soon as the involved chemistry becomes more ambitious …”

Energy transfer in supramolecular materials for new applications in photonics and electronics

“…Another potential route to well-defined architectures grafted onto solid substrates has been developed by the Matile group, and consists of the surface-initiated supramolecular polymerization process. [86][87][88][89] It has been successfully applied to obtaining redox gradients, and energy transfer across such structures comprising multiple chromophores is expected to be particularly efficient.…”