Dipolar Photosystems: Engineering Oriented Push-Pull Components into Double- and Triple-Channel Surface Architectures

Push–pull aromatics are not popular as optoelectronic materials because their supramolecular organization is difficult to control. However, recent progress with synthetic methods has suggested that the directional integration of push–pull components into multicomponent photosystems should become possible. In this study, we report the design, synthesis, and evaluation of double- or triple-channel architectures that contain π stacks with push–pull components in parallel or mixed orientation. Moreover, the parallel push–pull stacks were uniformly oriented with regard to co-axial stacks, either with inward or outward oriented push–pull dipoles. Hole-transporting (p) aminoperylenemonoimides (APIs) and aminonaphthalimides (ANIs) are explored for ordered push–pull stacks. For the co-axial electron-transporting (n) stacks, naphthalenediimides (NDIs) are used. In double-channel photosystems, mixed push–pull stacks are overall less active than parallel push–pull stacks. The orientation of the parallel push–pull stacks with regard to the co-axial NDI stacks has little influence on activity. In triple-channel photosystems, outward-directed dipoles in bridging stacks between peripheral p and central n channels show higher activity than inward-directed dipolar stacks. Higher activities in response to direct irradiation of outward-directed parallel stacks reveal the occurrence of quite remarkable optical gating

Toward Oriented Surface Architectures with Three Coaxial Charge-Transporting Pathways

We report a synthetic method to build oriented architectures with three coaxial π-stacks directly on solid surfaces. The approach operates with orthogonal dynamic bonds, disulfides and hydrazones, self-organizing surface-initiated polymerization (SOSIP), and templated stack-exchange (TSE). Compatibility with naphthalenediimides, perylenediimides, squaraines, fullerenes, oligothiophenes, and triphenylamine is confirmed. Compared to photosystems composed of two coaxial channels, the installation of a third channel increases photocurrent generation up to 10 times. Limitations concern giant stack exchangers that fail to enter SOSIP architectures (e.g., phthalocyanines surrounded by three fullerenes), and planar triads that can give folded or interdigitated charge-transfer architectures rather than three coaxial channels. The reported triple-channel surface architectures are as sophisticated as it gets today, the directionality of their construction promises general access to multichannel architectures with multicomponent gradients in each individual channel. The reported approach will allow us to systematically unravel the ultrafast photophysics of molecular dyads and triads in surface architectures, and might become useful to develop conceptually innovative optoelectronic devices

Antiparallel three-component gradients in double-channel surface architectures

The synthesis of multicomponent surface architectures with a thus far inaccessible level of sophistication is accomplished, and the functional relevance of this unprecedented structural complexity is demonstrated. Co-axial channels of oligothiophenes and fullerenes for the transport of holes and electrons, respectively, are equipped with antiparallel-oriented redox gradients with up to three components that drive the charges apart after their generation with light. In the resulting photosystems, charge recombination decreases with each level of sophistication from 29% to 2%, approaching complete suppression. Photocurrents increase correspondingly, and thermal activation barriers decrease. Increasing turn-on voltages for dark current indicates that charges struggle to move backwards up gradients possessing increasing numbers of components. These results demonstrate that the application of the most complex lessons from nature to organic materials is possible and worthwhile, thus supporting curiosity-driven efforts to learn how to synthesize multicomponent architectures of the highest possible sophistication with the highest possible precision

A Collection of Fullerenes for Synthetic Access Toward Oriented Charge-Transfer Cascades in Triple-Channel Photosystems

The development of synthetic methods to build complex functional systems is a central and current challenge in organic chemistry. This goal is important because supramolecular architectures of highest sophistication account for function in nature, and synthetic organic chemistry, contrary to high standards with small molecules, fails to deliver functional systems of similar complexity. In this report, we introduce a collection of fullerenes that is compatible with the construction of multicomponent charge-transfer cascades and can be placed in triple-channel architectures next to stacks of oligothiophenes and naphthalenediimides. For the creation of this collection, modern fullerene chemistry—methanofullerenes and 1,4-diarylfullerenes—is combined with classical Nierengarten–Diederich–Bingel approaches

Self-organizing surface-initiated polymerization, templated self-sorting and templated stack exchange: synthetic methods to build complex systems

In nature, spectacular function is achieved by highly sophisticated supramolecular architectures. Little is known what we would obtain if we could create complexity with similar precision, because the synthetic methods to do so are not available. This account summarizes recent approaches conceived to improve on this situation. With self-organizing surface-initiated polymerization (SOSIP), charge-transporting stacks can be grown directly on solid substrates with molecular-level precision. The extension to templated self-sorting (SOSIP-TSS) offers a supramolecular approach to multicomponent architectures. A solid theoretical framework for the transcription of information by templated self-sorting has been introduced, intrinsic templation efficiencies up to 97% have been achieved, and the existence of self-repair has been shown. The extension to templated stack exchange (SOSIP-TSE) offers the complementary covalent approach. Compatibility of this robust method with the creation of double-channel architectures with antiparallel two-component gradients has been demonstrated