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Impact of charge switching stimuli on supramolecular perylene monoimide assemblies.

ABSTRACT: The development of stimuli-responsive amphiphilic supramolecular nanostructures is an attractive target for systems based on light-absorbing chromophores that can function as photosensitizers in water. We report here on a water soluble supramolecular carboxylated perylene monoimide system in which charge can be switched significantly by a change in pH. This was accomplished by substituting the perylene core with an ionizable hydroxyl group. In acidic environments, crystalline supramolecular nanoribbons with dimensions on the order of 500 × 50 × 2 nm form readily, while in basic solution the additional electrostatic repulsion of the ionized hydroxyl reduces assemblies to very small dimensions on the order of only several nanometers. The HOMO/LUMO levels were also found to be sensitive to pH; in acidic media the HOMO/LUMO levels are -5.65 and -3.70 eV respectively versus vacuum, whereas is in basic conditions they are -4.90 and -3.33 eV, respectively. Utilizing the assemblies as photosensitizers in photocatalytic production of hydrogen with [Mo₃S₁₃]^2- as a catalyst at a pH of 4, H₂ was generated with a turnover number of 125 after 18 hours. Charge switching the assemblies at a pH of 9-10 and using an iron porphyrin catalyst, protons could again be reduced to hydrogen and CO₂ was reduced to CO with a turnover number of 30. The system investigated offers an example of dynamic photosensitizing assemblies that can drive reactions in both acidic and basic media.

SUBMITTER: Dannenhoffer A

PROVIDER: S-EPMC6568310 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature

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Impact of charge switching stimuli on supramolecular perylene monoimide assemblies.

Dannenhoffer Adam A Sai Hiroaki H Huang Dongxu D Nagasing Benjamin B Harutyunyan Boris B Fairfield Daniel J DJ Aytun Taner T Chin Stacey M SM Bedzyk Michael J MJ Olvera de la Cruz Monica M Stupp Samuel I SI

Chemical science 20190514 22

The development of stimuli-responsive amphiphilic supramolecular nanostructures is an attractive target for systems based on light-absorbing chromophores that can function as photosensitizers in water. We report here on a water soluble supramolecular carboxylated perylene monoimide system in which charge can be switched significantly by a change in pH. This was accomplished by substituting the perylene core with an ionizable hydroxyl group. In acidic environments, crystalline supramolecular nano ...[more]

PMID: 31293765

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Project description:CONSPECTUS: Supramolecular assemblies formed from spontaneous self-assembly of amphiphilic macromolecules are explored as biomimetic architectures and for applications in areas such as sensing, drug delivery, and diagnostics. Macromolecular assemblies are usually preferred, compared with their simpler small molecule counterparts, due to their low critical aggregate concentrations (CAC) and high thermodynamic stability. This Account focuses on the structural and functional aspects of assemblies formed from dendrimers, specifically facially amphiphilic dendrons that form micelle or inverse micelle type supramolecular assemblies depending on the nature of the solvent medium. The micelle type assemblies formed from facially amphiphilic dendrons sequester hydrophobic guest molecules in their interiors. The stability of these assemblies is dependent on the relative compatibility of the hydrophilic and hydrophobic functionalities with water, often referred to as hydrophilic-lipophilic balance (HLB). Disruption of the HLB, using an external stimulus, could lead to disassembly of the aggregates, which can then be utilized to cause an actuation event, such as guest molecule release. Studying these possibilities has led to (i) a robust and general strategy for stimulus-induced disassembly and molecular release and (ii) the introduction of a new approach to protein-responsive supramolecular disassembly. The latter strategy provides a particularly novel avenue for impacting biomedical applications. Most of the stimuli-sensitive supramolecular assemblies have been designed to be responsive to factors such pH, temperature, and redox conditions. The reason for this interest stems from the fact that certain disease microenvironments have aberrations in these factors. However, these variations are the secondary imbalances in biology. Imbalances in protein activity are the primary reasons for most, if not all, human pathology. There have been no robust strategies in stimulus-responsive assemblies that respond to these variations. The facially amphiphilic dendrimers provide a unique opportunity to explore this possibility. Similarly, the propensity of these molecules to form inverse micelles in apolar solvents and thus bind polar guest molecules, combined with the fact that these assemblies do not thermodynamically equilibrate in biphasic mixtures, was used to predictably simplify peptide mixtures. The structure-property relationships developed from these studies have led to a selective and highly sensitive detection of peptides in complex mixtures. Selectivity in peptide extraction was achieved using charge complementarity between the peptides and the hydrophilic components present in inverse micellar interiors. These findings will have implications in areas such as proteomics and biomarker detection.

Project description:Dye-sensitisation of TiO2 and other metal oxides is an established strategy to couple solar light harvesting with efficient charge separation for the production of electricity in dye-sensitised solar cells (DSCs) or fuels in dye-sensitised semiconductor photocatalysis (DSP). Perylene monoimide (PMI) dyes have emerged as promising organic dyes, but they have not previously been used in a functional assembly with TiO2 in aqueous solution. Here, five novel PMI dyes bearing carboxylic acid, phosphonic acid, acetylacetone, hydroxyquinoline or dipicolinic acid anchoring groups for attachment onto TiO2 are reported. We identified functional DSC and DSP systems with PMI-sensitised TiO2 in aqueous solution, which permitted a side-by-side comparison with respect to performance between the two systems. Structure-activity relationships allowed us to suggest anchor-condition-system associations to suit specific anchoring groups at various pH values, and with different electron mediators (redox couple or sacrificial electron donor) and catalysts in DSC and DSP schemes. A DSC sensitised with the hydroxyquinoline-modified PMI dye reached the highest short-circuit current density (J SC ≈ 1.4 mA cm-2) in aqueous electrolyte solution during irradiation with simulated solar light. This dye also achieved a turnover number (TONPMI) of approximately 4900 for sacrificial proton reduction after 24 h irradiation in a DSP scheme with Pt as a H2-evolving co-catalyst at pH 4.5. This performance was only surpassed by the carboxylic acid-bearing dye, which reached a new benchmark turnover number (TONPMI ≈ 1.1 × 104 after 72 h) for an organic dye in nanoparticulate DSP for solar fuel production. At higher pH (8.5), our results showed that the phosphonic acid group allows for higher performance due to a stronger anchoring ability. This study provides a platform for aqueous PMI dye-sensitised TiO2 chemistry and gives valuable insights into the performance of different anchoring groups in DSC and DSP systems.

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Impact of charge switching stimuli on supramolecular perylene monoimide assemblies.

Publications

Impact of charge switching stimuli on supramolecular perylene monoimide assemblies.

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