Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission

Hart, S. R.; Silva, W. Ruchira; Frontiera, Renee R.

doi:10.1039/c7sc03496b

Cited by 73 publications

(87 citation statements)

References 47 publications

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“…Since Mathies and co-workers first introduced the femtosecond stimulated Raman spectroscopy (FSRS) to the ultrafast dynamics and transient Raman measurements of all-trans-β-carotene in the S 2 and S 1 excited states [39,40], FSRS with both high spectral (<10 cm −1 ) and temporal (<50 fs) resolutions has been widely applied to many excited state processes including the intra-and inter-molecular proton transfers [41][42][43][44], charge transfers [45][46][47][48], electron transfers [49][50][51][52]. A broadband Raman probe pulses combined with a narrowband Raman pump were used for FSRS, and the transient Raman bands of the ground and excited electronic states can be obtained at the same time in a wide frequency range covering most of the fingerprint region (800-2200 cm −1 ) [43,53].…”

Section: Introductionmentioning

confidence: 99%

Twisted Intramolecular Charge Transfer State of a “Push-Pull” Emitter

Lee

Jen

Pang

2020

IJMS

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The excited state Raman spectra of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) in the locally-excited (LE) and the intramolecular charge transfer (ICT) states have been separately measured by time-resolved stimulated Raman spectroscopy. In a polar dimethylsulfoxide solution, the ultrafast ICT of DCM with a time constant of 1.0 ps was observed in addition to the vibrational relaxation in the ICT state of 4–7 ps. On the other hand, the energy of the ICT state of DCM becomes higher than that of the LE state in a less polar chloroform solution, where the initially-photoexcited ICT state with the LE state shows the ultrafast internal conversion to the LE state with a time constant of 300 fs. The excited-state Raman spectra of the LE and ICT state of DCM showed several major vibrational modes of DCM in the LE and ICT conformer states coexisting in the excited state. Comparing to the time-dependent density functional theory simulations and the experimental results of similar push-pull type molecules, a twisted geometry of the dimethylamino group is suggested for the structure of DCM in the S1/ICT state.

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Section: Introductionmentioning

confidence: 99%

Twisted Intramolecular Charge Transfer State of a “Push-Pull” Emitter

Lee

Jen

Pang

2020

IJMS

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“…In the past decade, femtosecond stimulated Raman spectroscopy (FSRS) has become a powerful spectroscopic methodology that can provide the equilibrium and non-equilibrium vibrational signatures and track excited-state molecular dynamics with simultaneously high spectral and temporal resolutions [1][2][3][4][5][6][7]. Over recent years, a great variety of chemically and biologically relevant systems have been studied by FSRS spanning from organic photoacids and chromophores [8][9][10][11][12][13][14][15], molecular rotors [16], fluorescent proteins [3,17], photoreceptor proteins [18][19][20][21][22][23][24][25][26], calcium biosensors [4,[27][28][29], metal complexes [30,31], materials [32][33][34], and engineered molecular systems [35,36]. The underlying photophysical and photochemical processes including excited-state proton transfer, charge transfer, vibrational cooling, internal conversion, isomerization, and bond dissociation have been successfully revealed and discussed in the larger context of effectively delineating the structure-energy-function relationships [6,7].…”

Section: Introductionmentioning

confidence: 99%

Femtosecond stimulated Raman line shapes: Dependence on resonance conditions of pump and probe pulses

Chen

Zhu

Fang

2018

Chinese Journal of Chemical Physics

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Resonance enhancement has been increasingly employed in the emergent femtosecond stimulated Raman spectroscopy (FSRS) to selectively monitor molecular structure and dynamics with improved spectral and temporal resolutions and signal-to-noise ratios. Such joint efforts by the technique-and application-oriented scientists and engineers have laid the foundation for exploiting the tunable FSRS methodology to investigate a great variety of photosensitive systems and elucidate the underlying functional mechanisms on molecular time scales. During spectral analysis, peak line shapes remain a major concern with an intricate dependence on resonance conditions. Here, we present a comprehensive study of line shapes by tuning the Raman pump wavelength from red to blue side of the ground-state absorption band of the fluorescent dye rhodamine 6G in solution. Distinct line shape patterns in Stokes and anti-Stokes FSRS as well as from the low to high-frequency modes highlight the competition between multiple third-order and higher-order nonlinear pathways, governed by different resonance conditions achieved by Raman pump and probe pulses. In particular, the resonance condition of probe wavelength is revealed to play an important role in generating circular line shape changes through oppositely phased dispersion via hot luminescence (HL) pathways. Meanwhile, on-resonance conditions of the Raman pump could promote excited-state vibrational modes which are broadened and red-shifted from the coincident ground-state vibrational modes, posing challenges for spectral analysis. Certain strategies in tuning the Raman pump and probe to characteristic regions across an electronic transition band are discussed to improve the FSRS usability and versatility as a powerful structural dynamics toolset to advance chemical, physical, materials, and biological sciences.

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“…In addition, because the singlet fission conserves the spin angular momentum of charge carriers, the process can occur extremely fast (on picosecond down to femtosecond time scales), even faster than radiative decay which is on a nanosecond timescale, thus generating triplet pairs (or triplets) very efficiently. [17,28] Energetically, singlet fission requires a molecular system to have twice its triplet excitation energy either equal to (isoergic) or less than (exoergic) the energy of its singlet excitation -that is, 2E(T 1 ) � E(S 1 ). Even when 2E(T 1 ) > E(S 1 ) (endoergic), if the difference between 2E(T 1 ) and E(S 1 ) is smaller than thermal energy, singlet fission can take place.…”

Section: Magnetic Field Effects (Mfes) In Singlet Fissionmentioning

confidence: 99%

“…When organic chromophores are oriented to have a large electronic coupling between singlet and paired triplet state, it can lead to the singlet fission. In addition, because the singlet fission conserves the spin angular momentum of charge carriers, the process can occur extremely fast (on picosecond down to femtosecond time scales), even faster than radiative decay which is on a nanosecond timescale, thus generating triplet pairs (or triplets) very efficiently …”

Section: Magnetic Field Effects (Mfes) In Singlet Fissionmentioning

confidence: 99%

The Effect of Magnetic Fields on Singlet Fission in Organic Semiconductors: its Understanding and Applications

Jang

2020

ChemPhotoChem

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Singlet fission is a photophysical process in which one singlet excited state converts into two triplet excited states in a molecular system. Singlet fission has gained much attention in photovoltaic technology and the interest in singlet fission stems from the possibility of drastically increasing the efficiency of solar cells. Since singlet fission is a spin-dependent phenomenon, its dynamic process can be altered and influenced by an external magnetic field. The effect of magnetic fields on singlet fission in molecular materials has been utilized to deliver a better understanding of the phenomenon and even to enhance it. This Minireview provides an overview and an insight on recent developments as well as traditional approaches of how the magnetic field effects in organic molecular systems can be taken advantage of to elucidate the fundamental dynamics of singlet fission process, and furthermore to improve it in technological applications.

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Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission

Abstract: Evidence for transient anionic and cationic species in singlet fission is given by ultrafast Raman measurements.

Cited by 73 publications

References 47 publications

Twisted Intramolecular Charge Transfer State of a “Push-Pull” Emitter

Twisted Intramolecular Charge Transfer State of a “Push-Pull” Emitter

Femtosecond stimulated Raman line shapes: Dependence on resonance conditions of pump and probe pulses

The Effect of Magnetic Fields on Singlet Fission in Organic Semiconductors: its Understanding and Applications

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