Syntheses, structures, and supramolecular properties of giant π‐expanded macrocyclic oligothiophenes

Iyoda, Masahiko

doi:10.1002/hc.20337

Cited by 21 publications

(9 citation statements)

References 75 publications

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“…Polarized absorption and emission studies of bent or curved molecular aggregates and polymers have provided additional insight into exciton localization and photophysics. − In this regard, conjugated polymers (CPs) can be effectively modeled as linear J-aggregates (“J-chains”), where each repeat unit represents a chromophore as depicted in Figure . ,− The uniform chain bend is quantified by the angle θ between adjacent repeat unit (transition) dipole moment vectors; in the all-syn conformation of P3HT shown in Figure , θ is well-defined. However, even ostensibly “straight” polymers (for example, all-anti-P3HT) can undergo long-range bending stress, which induces a curved topology.…”

Section: Absorption and Photoluminescence In Vibronically Coupled H- ...mentioning

confidence: 99%

Expanded Theory of H- and J-Molecular Aggregates: The Effects of Vibronic Coupling and Intermolecular Charge Transfer

2018

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The electronic excited states of molecular aggregates and their photophysical signatures have long fascinated spectroscopists and theoreticians alike since the advent of Frenkel exciton theory almost 90 years ago. The influence of molecular packing on basic optical probes like absorption and photoluminescence was originally worked out by Kasha for aggregates dominated by Coulombic intermolecular interactions, eventually leading to the classification of J- and H-aggregates. This review outlines advances made in understanding the relationship between aggregate structure and photophysics when vibronic coupling and intermolecular charge transfer are incorporated. An assortment of packing geometries is considered from the humble molecular dimer to more exotic structures including linear and bent aggregates, two-dimensional herringbone and "HJ" aggregates, and chiral aggregates. The interplay between long-range Coulomb coupling and short-range charge-transfer-mediated coupling strongly depends on the aggregate architecture leading to a wide array of photophysical behaviors.

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Section: Absorption and Photoluminescence In Vibronically Coupled H- ...mentioning

confidence: 99%

Expanded Theory of H- and J-Molecular Aggregates: The Effects of Vibronic Coupling and Intermolecular Charge Transfer

2018

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“…Most CP assemblies assume complex morphologies; random coils, molten globules, toroids, rods, defect-coils, and defect-cylinders are all possibilities depending on the chain stiffness, the interactions between chain segments, and the interactions between the chain and the surrounding medium . On the other hand, ordered and sometimes exotic CP structures are either known or have been suggested, including straight, practically disorder-free polydiacetylene chains polymerized within their monomer matrix; solvent induced, single molecule aggregates of polythiophene with a suggested helical structure; an extensive range of macrocyclic oligothiohenes; , circular porphyrin nanorings; − and virtually defect-free, bending-in-plane β-phase polyfluorene molecules . With the abundant diversity of possible backbone conformations available to CP chains, the question of the effect of morphology on the optical properties naturally arises.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Chain Bending on the Photophysical Properties of Conjugated Polymers

Hestand

Spano

2014

J. Phys. Chem. B

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The impact of chain bending on the photophysical properties of emissive conjugated polymers (CPs) is studied theoretically using Holstein-style Hamiltonians which treat vibronic coupling involving the ubiquitous vinyl/ring stretching mode nonadiabatically. The photophysical impact of chain bending is already evident at the level of an effective Frenkel Hamiltonian, where the positive exciton band curvature in CPs translates to negative excitonic coupling between monomeric units, as in J-aggregates. It is shown that the absorption and photoluminescence (PL) spectral line shapes respond very differently to chain bending. The misalignment of monomeric transition dipole moments with bending selectively attenuates the 0-0 PL peak intensity while leaving the 0-1 intensity practically unchanged, a property which is ultimately due to the uniquely coherent nature of the 0-0 peak. Hence, the 0-0/0-1 PL ratio, as well as the radiative decay rate, decrease with chain bending, effects that are more pronounced at lower temperatures where exciton coherence extends over a larger portion of the chain. Increasing temperature and/or static disorder reduces the exciton coherence number, Ncoh, thereby reducing the sensitivity to bending. In marked contrast, the absorption vibronic progression is far less sensitive to morphological changes, even at low temperatures, and is mainly responsive to the exciton bandwidth. The above results also hold when using a more accurate 1D semiconductor Hamiltonian which allows for electron-hole separation along the CP chain. The findings may suggest unique ways of controlling the radiative properties of conjugated polymer chains useful in applications such as organic light emitting diodes (OLEDs) and low-temperature sensors.

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“…Many oligo- and polythiophene compounds have attracted recent interest for use in optical and electronic devices due to their reported fluorescence and conducting properties. − The properties of shorter oligomers are known to be greatly influenced by “end-effects”. ,, Dendritic structures have also been studied to determine their potential for use in artificial light-harvesting systems. − These structures have the advantage of controlled synthesis that results in regular and well-defined architectures, and their photophysical processes are strongly affected by their geometrical confinement. − However, issues related to end effects and very high flexibility are known to limit the possibilities of these structures . Cyclic molecular aggregates, however, are well-known to play a crucial role in very efficient natural photosynthetic systems. , Previous studies have shown that long conjugation associated with relatively rigid and ordered cyclic morphology in synthetic structures leads to strongly enhanced nonlinear optical responses. − Recently developed thiophene-based macrocycles offer new materials that combine potentially endless π-conjugation paths with structurally well-defined oligomers. − The outstanding electrical properties of oligothiophene systems have already shown success in organic photovoltaic cells. , By combining these materials with a cyclic topology shown to be efficient in light-harvesting antenna, we are able to gain a novel perspective in the development of efficient light conversion devices that utilize quantum coherence.…”

Section: Introductionmentioning

confidence: 99%

Probing Coherence in Synthetic Cyclic Light-Harvesting Pigments

et al. 2011

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A series of π-extended cyclic thiophene oligomers of 12, 18, 24, and 30 repeat units have been studied using methods of ultrafast time-resolved absorption, fluorescence upconversion, and three-pulse photon echo. These measurements were conducted in order to examine the structure-function relationships that may affect the coherence between chromophores within the organic macrocycles. Our results indicate that an initial delocalized state can be seen upon excitation of the cyclic thiophenes. Anisotropy measurements show that this delocalized state decays on an ultrafast time scale and is followed by the presence of incoherent hopping. From the use of a phenomenological model, we conclude that our ultrafast anisotropy decay measurements suggest that the system does not reside in the Förster regime and coherence within the system must be considered. Three-pulse photon echo peak shift experiments reveal a clear dependence of initial peak shift with ring size, indicating a weaker coupling to the bath (and stronger intramolecular interactions) as the ring size is increased. Our results suggest that the initial delocalized state increases with ring size to distances (and number of chromophores) comparable to the natural light-harvesting system.

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Syntheses, structures, and supramolecular properties of giant π‐expanded macrocyclic oligothiophenes

Abstract: ABSTRACT:Fully conjugated π-expanded macrocyclic oligothiophenes with 60π-, 90π-, 120π-, 150π-, and 180π-electron systems (1-5)

Cited by 21 publications

References 75 publications

Expanded Theory of H- and J-Molecular Aggregates: The Effects of Vibronic Coupling and Intermolecular Charge Transfer

Expanded Theory of H- and J-Molecular Aggregates: The Effects of Vibronic Coupling and Intermolecular Charge Transfer

The Effect of Chain Bending on the Photophysical Properties of Conjugated Polymers

Probing Coherence in Synthetic Cyclic Light-Harvesting Pigments

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