Torsional disorder and planarization dynamics: 9,10-bis(phenylethynyl)anthracene as a case study

Fureraj, Ina; Budkina, Darya S.; Vauthey, Eric

doi:10.1039/d2cp03909e

Cited by 9 publications

(12 citation statements)

References 76 publications

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“…In the energy-minimized structures for all dimers, we found a dihedral angle (θ) of nearly 0° between the pentacene plane and the adjacent ring of a linker. However, the acetylene (–CC–) bond is likely to be a significant source of conformational heterogeneity due to the shallow barrier for rotation around it. – Indeed, the potential energy scans in Figures b ( P2BP and P2BPMe ) and S3.2.2 (other dimers) show that all torsional conformers can exist at room temperature regardless of the linkage type with only a slight difference in the gradients of potential energy curves depending on the linkers. In contrast, torsion about the single bond within the linkers can be sharply restricted, and potential minima along the coordinate vary greatly.…”

Section: Resultsmentioning

confidence: 99%

Controlling Intramolecular Singlet Fission Dynamics via Torsional Modulation of Through-Bond versus Through-Space Couplings

Majumder,

Mukherjee,

Panjwani

et al. 2023

J. Am. Chem. Soc.

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Covalent dimers, particularly pentacenes, are the dominant platform for developing a mechanistic understanding of intramolecular singlet fission (iSF). Numerous studies have demonstrated that a photoexcited singlet state in these structures can rapidly and efficiently undergo exciton multiplication to form a correlated pair of triplets within a single molecule, with potential applications from photovoltaics to quantum information science. One of the most significant barriers limiting such dimers is the fast recombination of the triplet pair, which prevents spatial separation and the formation of long-lived triplet states. There is an ever-growing need to develop general synthetic strategies to control the evolution of triplets following iSF and enhance their lifetime. Here, we rationally tune the dihedral angle and interchromophore separation between pairs of pentacenes in a systematic series of bridging units to facilitate triplet separation. Through a combination of transient optical and spin-resonance techniques, we demonstrate that torsion within the linker provides a simple synthetic handle to tune the fine balance between through-bond and through-space interchromophore couplings that steer iSF. We show that the full iSF pathway from femtosecond to microsecond timescales is tuned through the static coupling set by molecular design and structural fluctuations that can be biased through steric control. Our approach highlights a straightforward design principle to generate paramagnetic spin pair states with higher yields.

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Section: Resultsmentioning

confidence: 99%

Controlling Intramolecular Singlet Fission Dynamics via Torsional Modulation of Through-Bond versus Through-Space Couplings

Majumder,

Mukherjee,

Panjwani

et al. 2023

J. Am. Chem. Soc.

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“…The S 1 energy of BPEAdim, as determined from the intersection of the absorption and emission signals, is red-shifted 0.027 eV relative to the monomer at 474 nm, and BPEAtri is shifted by an additional 0.027 eV. The unstructured absorption spectrum, in contrast to the structured emission, is attributed to excited state planarization, which has previously been studied in detail …”

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confidence: 79%

“…The unstructured absorption spectrum, in contrast to the structured emission, is attributed to excited state planarization, which has previously been studied in detail. 16 The photophysical properties of BPEAmono have been initially examined in both dilute and concentrated solutions to assess its suitability for SF. In dilute solution, BPEAmono has a fluorescence quantum yield close to unity and decays monoexponentially with a lifetime of approximately 3.4 ns (Figure 2a).…”

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confidence: 99%

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Triplet Formation in a 9,10-Bis(phenylethynyl)anthracene Dimer and Trimer Occurs by Charge Recombination Rather than Singlet Fission

Ringström,

Schroeder,

Mencaroni

et al. 2023

J. Phys. Chem. Lett.

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We present an experimental study investigating the solvent-dependent dynamics of a 9,10-bis(phenylethynyl)anthracene monomer, dimer, and trimer. Using transient absorption spectroscopy, we have discovered that triplet excited state formation in the dimer and trimer molecules in polar solvents is a consequence of charge recombination subsequent to symmetry-breaking charge separation rather than singlet fission. Total internal reflection emission measurements of the monomer demonstrate that excimer formation serves as the primary decay pathway at a high concentration. In the case of highly concentrated solutions of the trimer, we observe evidence of triplet formation without the prior formation of a charge-separated state. We postulate that this is attributed to the formation of small aggregates, suggesting that oligomers mimicking the larger chromophore counts in crystals could potentially facilitate singlet fission. Our experimental study sheds light on the intricate dynamics of the 9,10-bis(phenylethynyl)anthracene system, elucidating the role of solvent- and concentration-dependent factors for triplet formation and charge separation.

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“…Low barrier for torsion in conjugated molecules, like those containing phenyl–ethynyl building blocks, results in structural disorder at room temperature, − which can lead to a inhomogeneous broadening of the S 1 ←S 0 absorption band. In such cases, the excited-state dynamics may depend on the excitation wavelength. − Interestingly, faster ground-state recovery dynamics were reported upon red-edge excitation of CV. , Based on this, we wondered whether torsional disorder could also be at the origin of the shoulder of the absorption band of CV. Here, using stationary and time-resolved spectroscopy with polarization control, combined with quantum-chemical calculations, we show that there is indeed a distribution of ground-state geometries, that includes symmetric and symmetry-broken, torsionally disordered, structures.…”

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confidence: 99%

Torsional Disorder, Symmetry Breaking, and the Crystal Violet Shoulder Controversy

Sissaoui

Budkina

Vauthey

2023

J. Phys. Chem. Lett.

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The nature of the lowest-energy electronic absorption band of crystal violet (CV) and particularly the origin of its high-energy shoulder have been debated since the middle of the past century. The most recent studies invoke a splitting of the S1 state upon symmetry breaking induced by interactions with the solvent and/or the counterion. Using a combination of stationary and time-resolved polarized spectroscopy together with quantum-chemical calculations, we show that torsional disorder in the ground-state results in an inhomogeneous broadening of the absorption band of CV. The center of the band is mostly due to symmetric molecules with a degenerate S1 state, whereas the edges originate from transitions to the S1 and S2 states of distorted symmetry-broken molecules. Transient-absorption measurements with different excitation wavelengths reveal that these two groups of molecules interconvert rapidly in liquid but not in a rigid environment.

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Torsional disorder and planarization dynamics: 9,10-bis(phenylethynyl)anthracene as a case study

Abstract: Conjugated molecules with phenylethynyl building blocks are usually characterised by torsional disorder at room temperature. They are much more rigid in the electronic excited state due to conjugation. As a...

Cited by 9 publications

References 76 publications

Controlling Intramolecular Singlet Fission Dynamics via Torsional Modulation of Through-Bond versus Through-Space Couplings

Controlling Intramolecular Singlet Fission Dynamics via Torsional Modulation of Through-Bond versus Through-Space Couplings

Triplet Formation in a 9,10-Bis(phenylethynyl)anthracene Dimer and Trimer Occurs by Charge Recombination Rather than Singlet Fission

Torsional Disorder, Symmetry Breaking, and the Crystal Violet Shoulder Controversy

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