Generalized Kasha’s Model: T-Dependent Spectroscopy Reveals Short-Range Structures of 2D Excitonic Systems

Chuang, Chern; Bennett, Doran I. G.; Caram, Justin R.; Aspuru‐Guzik, Alán; Bawendi, Moungi G.; Cao, Jianshu

doi:10.1016/j.chempr.2019.08.013

Cited by 34 publications

(70 citation statements)

References 58 publications

(85 reference statements)

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“…To probe higher dimensional aggregate structures, one must go beyond aggregate to monomer absorption peak shifts and narrowing. Expanding on previous theories, 22,31 we present a classification system encompassing such diverse excitonic behaviors in 2D aggregates based on peak shifts and peak broadening with temperature as well as room temperature quantum yields. The following paragraph and Whereas, for aggregates with red shifted absorptions from their monomers, both I-and J-aggregation is possible.…”

Section: Resultsmentioning

confidence: 92%

Bridging the Gap between H- and J-Aggregates: Classification and Supramolecular Tunability for Excitonic Band Structures in 2-Dimensional Molecular Aggregates

Deshmukh

Geue

Bardbury

et al. 2021

Preprint

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Molecular aggregates with long-range excitonic couplings have drastically different photophysical properties compared to their monomer counterparts. From Kasha’s model for 1-dimensional systems, positive or negative excitonic couplings lead to blue or red shifted optical spectra with respect to the monomers, labelled H-and J-aggregates respectively. The overall excitonic couplings in higher dimensional systems are much more complicated and cannot be simply classified from their spectral shifts alone. Here, we provide a unified classification for extended 2D aggregates using temperature dependent peak shifts, thermal broadening and quantum yields. We discuss the examples of six 2D aggregates with J-like absorption spectra but quite drastic changes quantum yields and superradiance. We find the origin of the differences is, in fact, a different excitonic band structure where the bright state is lower energy than the monomer but still away from the band edge. We call this an ‘I-aggregate’. Our results provide a description of the complex excitonic behaviors that cannot be explained solely on Kasha’s model. Further, such properties can be tuned with the packing geometries within the aggregates providing supramolecular pathways for controlling them. This will allow for precise optimizations of aggregate properties in their applications across the areas of optoelectronics, photonics, excitonic energy transfer, and shortwave infrared technologies.

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Section: Resultsmentioning

confidence: 92%

Bridging the Gap between H- and J-Aggregates: Classification and Supramolecular Tunability for Excitonic Band Structures in 2-Dimensional Molecular Aggregates

Deshmukh

Geue

Bardbury

et al. 2021

Preprint

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“…Understanding how these structures are stabilized and thereby controlling aggregate formation is a prerequisite to realizing their vast technological and therapeutic applications. While many studies have elucidated the excitonic features of 2D and tubular cyanine aggregates and related it to their supramolecular structure, [38][39][40] little work has been done in understanding how these structures are stabilized. In Table 1, we summarize the common literature protocols used to prepare the J-aggregates with the characteristic narrow red shifted absorption for various benzothiazole cyanine dyes ( Figure 1).…”

Section: Aggregate Preparation Strategymentioning

confidence: 99%

Principles for Self-Assembly of Cyanine Dyes into 2-Dimensional Excitonic Aggregates Across the Visible and Near-Infrared

Deshmukh

Bailey²,

Forte³

et al. 2020

Preprint

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<div>Cyanine dyes show a remarkable tendency to form non-covalent supramolecular aggregates with diverse morphologies (dimers, sheets, tubes and bundles). Specific molecular arrangements within these H- or J-aggregates dictate the extraordinary photophysical properties, including long-range exciton delocalization, extreme redshifts, and excitonic superradiance. Despite extensive literature on cyanine dye aggregates, design principles that drive the solution self-assembly to a preferred H- or J-aggregated state are unknown. We present a general approach to tune the thermodynamics of self-assembly, selectively stabilizing H- or J-aggregates and thereby achieving supramolecular control over aggregate photophysics. A simple interplay of solvent to non-solvent ratio, ionic strength or dye concentration yields a broad range of conditions that predictably and preferentially stabilize the monomer, H- or J-aggregate species that can be easily monitored using absorption spectroscopy. Diffusion ordered spectroscopy, cryo-electron microscopy and atomic force microscopy together reveal a dynamic equilibrium between monomers, H-aggregated dimers, and extended J-aggregated 2-dimensional monolayers. This structural information informs a three-component equilibrium model that describes the observed concentration dependence of spectral signatures, showing excellent fit with experimental data and yields the Gibb’s free energies of self-assembly for dimerization and 2D aggregate assembly. We further demonstrate the universality of this approach among several sheet forming cyanine dyes including the benzothiazole and benzimidazole families with absorptions spanning visible, near and shortwave infrared wavelengths.</div>

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“…Molecular aggregates play a crucial role in natural photosynthetic light harvesting and hold great promise for artificial devices with novel photophysical properties. Although the properties of linear molecular aggregates are well understood in terms of Kasha's model, 1 more complex structural assemblies such as tubes, 2-5 sheets, 6,7 and ribbons 5 pose important challenges for the understanding of structure-function relationships. For example, spectral changes resulting from thermal changes in merocyanine dye monolayers 7 cannot be understood in terms of rules established for linear aggregates.…”

Section: Previewmentioning

confidence: 99%

“…As the temperature rises, the disorder will perturb the exciton states and the exciton absorption peak will move further down in energy 10 (Figure 1 from Chuang et al 1 ). In contrast, when the angle between the transition dipoles and the aggregate axis is larger than the magic angle, the super-radiant states will emerge at the top of the exciton band and they will move further up in energy as the temperature increases.…”

Section: Previewmentioning

confidence: 99%

“…The supported metal catalysts exhibit excellent activity and/or selectivity in various industrial reactions, such as hydroalkylation, hydrogenation, dehydro-genation, hydrocracking, isomerization, and so on. 1 As the particles are downsized to single atoms, the obtained single-atom catalysts (SACs) have the maximum atom efficiency and are strongly preferred for catalysis-related reactions. 2 However, the SACs suffer from the high tendency to self-aggregate into nanoparticles (NPs) because of high surface energy.…”

Section: Previewmentioning

confidence: 99%

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Unraveling Molecular Packing in Two-Dimensional Excitonic Systems

Jansen

2019

Chem

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Generalized Kasha’s Model: T-Dependent Spectroscopy Reveals Short-Range Structures of 2D Excitonic Systems

Cited by 34 publications

References 58 publications

Bridging the Gap between H- and J-Aggregates: Classification and Supramolecular Tunability for Excitonic Band Structures in 2-Dimensional Molecular Aggregates

Bridging the Gap between H- and J-Aggregates: Classification and Supramolecular Tunability for Excitonic Band Structures in 2-Dimensional Molecular Aggregates

Principles for Self-Assembly of Cyanine Dyes into 2-Dimensional Excitonic Aggregates Across the Visible and Near-Infrared

Unraveling Molecular Packing in Two-Dimensional Excitonic Systems

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