Optical Projection and Spatial Separation of Spin-Entangled Triplet Pairs from the S1 (21 Ag–) State of Pi-Conjugated Systems

Pandya, Raj; Gu, Qifei; Cheminal, Alexandre; Chen, Richard Y. S.; Booker, Edward P.; Soucek, Richard; Schott, M.; Legrand, Laurent; Mathevet, Fabrice; Barisien, Thierry; Musser, Andrew J.; Chin, Alex W.; Rao, Akshay

doi:10.1016/j.chempr.2020.09.011

Cited by 18 publications

(35 citation statements)

References 130 publications

(250 reference statements)

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“…In “blue” PDA, the pump–probe spectrum is characterized by a sharp stimulated emission (SE) band at 650 nm, a broad photoinduced absorption (PIA) at 750–900 nm and a second narrower PIA at 680–700 nm (Figure c). By using spectral decomposition methods outlined in a previous study and fitting the electronic decays (exponential decay convoluted with instrument response) we find that the SE (1 1 B u + ) decays monoexponentially to the ground state with a lifetime of 630 ± 10 fs, while the PIA at 750–900 nm decays with a lifetime 1300 ± 40 fs and the PIA at 680–700 nm with 2300 ± 130 fs. The observed excited-state features and dynamics agree excellently with previous reports. ,, Following this agreement, we can assign the SE band to 1 1 B u + (S 2 ), the broad PIA is attributed to the 2 1 A g – (S 1 ) state and the narrow PIA at 680–700 nm to a hot, vibrationally excited, ground state. − Photoexcitation of “blue” PDA to 1 1 B u + (S 2 ) is thus followed by rapid internal conversion within 90 fs to 2 1 A g – (S 1 ) (i.e., rise time for 2 1 A g – kinetic as derived following spectral decompostion) which decays back to the ground state.…”

Section: Resultsmentioning

confidence: 90%

“…For “blue” PDA we probed in the center of the 2 1 A g – PIA band at 800 nm (blue stripes in Figure c), while the probe wavelength in “red” PDA was set to 790 nm to be centered with the 1 1 B u + PIA (orange stripes in Figure d). Spectral decomposition based on previous studies demonstrates that this wavelength ensures that we exclusively monitor the S 1 exciton population, free of other spectral features. This point is discussed further in SI Section S2 where we report the probe wavelength dependence of the fs-TAM demonstrating the “hot” exciton and S 1 diffusion properties to be distinct.…”

Section: Resultsmentioning

confidence: 95%

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Exciton Diffusion in Highly-Ordered One Dimensional Conjugated Polymers: Effects of Back-Bone Torsion, Electronic Symmetry, Phonons and Annihilation

Pandya

Alvertis

et al. 2021

J. Phys. Chem. Lett.

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Many optoelectronic devices based on organic materials require rapid and long-range singlet exciton transport. Key factors controlling exciton transport include material structure, exciton–phonon coupling and electronic state symmetry. Here, we employ femtosecond transient absorption microscopy to study the influence of these parameters on exciton transport in one-dimensional conjugated polymers. We find that excitons with 2 1 A g – symmetry and a planar backbone exhibit a significantly higher diffusion coefficient (34 ± 10 cm 2 s –1 ) compared to excitons with 1 1 B u + symmetry (7 ± 6 cm 2 s –1 ) with a twisted backbone. We also find that exciton transport in the 2 1 A g – state occurs without exciton–exciton annihilation. Both 2 1 A g – and 1 1 B u + states are found to exhibit subdiffusive behavior. Ab initio GW -BSE calculations reveal that this is due to the comparable strengths of the exciton–phonon interaction and exciton coupling. Our results demonstrate the link between electronic state symmetry, backbone torsion and phonons in exciton transport in π-conjugated polymers.

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Section: Resultsmentioning

confidence: 90%

Section: Resultsmentioning

confidence: 95%

Exciton Diffusion in Highly-Ordered One Dimensional Conjugated Polymers: Effects of Back-Bone Torsion, Electronic Symmetry, Phonons and Annihilation

Pandya

Alvertis

et al. 2021

J. Phys. Chem. Lett.

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“…Since their synthesis by Wegner, PDAs have attracted broad attention due to their potential use as sensors. PDAs formed from long-chain carboxylic acid DAs exhibit unique chromatic transitions from a visibly blue, nonfluorescent phase to a red, fluorescent phase. , This blue to red chromatic transition can be exploited for use as novel colorimetric sensors, which have been summarized in several notable reviews. − The mechanism of these transitions is still not fully characterized, with both the electronic − and the structural nature of the transition still under investigation …”

Section: Introductionmentioning

confidence: 99%

Characterizing and Tuning the Properties of Polydiacetylene Films for Sensing Applications

et al. 2021

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Self-assembled, polymerized diacetylene (DA) nanostructures and two-dimensional films have been studied over the past two decades for sensor applications because of their straightforward visual readout. DA monomers, when exposed to UV light, polymerize to produce a visibly blue polymer. Blue phase polydiacetylenes (PDAs) when exposed to an external stimuli, such as temperature or UV light, undergo a chromatic phase transition to a fluorescent, visibly red phase. The tunability of the monomer to blue to red chromatic phase transitions by choice of diacetylene monomer in the presence of metal cations is systematically and comprehensively investigated to determine their effects on the properties of PDA Langmuir films. The polymerization kinetics and domain morphology of the PDA films were characterized using polarized fluorescent microscopy, UV−vis−fluorescent spectroscopy, and Fourier transform infrared spectroscopy (FTIR). Increasing the monomer alkyl tail length was found to strongly increase the UV dose necessary to produce optimally blue films and fully red films. A decrease in the polymer domain size was also correlated with longer-tailed DA molecules. Metal cations have a diverse effect on the film behavior. Alkaline-earth metals such as Mg, Ca, and Ba have a negligible effect on the phase transition kinetics but can be used to tune PDA polymer domain sizes. The Ni and Fe cations increase the UV dose necessary to produce red phase PDA films and significantly decrease the polymer domain sizes. The Zn, Cd, and Cu ions exhibit strong directed interactions with the PDA carboxylic acid headgroups, resulting in quenched fluorescence and a unique film morphology. FTIR analysis provides insight into the metal−PDA binding mechanisms and demonstrates that the coordination between the PDA film headgroups and the metal cations can be correlated with changes in the film morphology and kinetics. The findings from these studies will have broad utility for tuning PDA-based sensors for different applications and sensitivity ranges.

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“…Experimentally it has been observed in π-conjugated polymers, e.g., polydiacetylene [14] and oligo(thienylenevinylenes) [15], that an optical excitation above the S 2 (i.e. 1 1 B + u ) manifold band edge leads to the creation of non-geminate pairs of triplets.…”

Section: Introductionmentioning

confidence: 99%

Triplet-Triplet Decoherence in Singlet Fission

Marcus,

Barford

2020

Preprint

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Singlet fission is commonly defined to involve a process by which an overall singlet state with local triplet structure spin-decoheres into two triplet states, thereby completing the fission process. This process, often defined in loose terms involving the multiplicity of the overall state, is investigated here using a uniform Heisenberg spin-chain subject to a dephasing environmental interaction. We introduce new results from quantum information theory which enables the quantification of coherence and entanglement in a bi-and multipartite system. The calculated measures of these quantum effects can be linked to observables, such as magnetisation and total spin, with simulations of the model and using theoretical methods. We demonstrate that these observables can act as a proxy for the coherence and entanglement measures. The decay of both of these between the two local triplets can be monitored, enabling a clear definition of the spin-decoherence process in singlet fission.

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Optical Projection and Spatial Separation of Spin-Entangled Triplet Pairs from the S1 (21 Ag–) State of Pi-Conjugated Systems

Cited by 18 publications

References 130 publications

Exciton Diffusion in Highly-Ordered One Dimensional Conjugated Polymers: Effects of Back-Bone Torsion, Electronic Symmetry, Phonons and Annihilation

Exciton Diffusion in Highly-Ordered One Dimensional Conjugated Polymers: Effects of Back-Bone Torsion, Electronic Symmetry, Phonons and Annihilation

Characterizing and Tuning the Properties of Polydiacetylene Films for Sensing Applications

Triplet-Triplet Decoherence in Singlet Fission

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