Photoinduced charge transfer involving a MoMo quadruply bonded complex to a perylene diimide

Alberding, Brian G.; Brown-Xu, Samantha E.; Chisholm, Malcolm H.; Epstein, Arthur J.; Gustafson, Terry L.; Lewis, Sharlene A.; Min, Yong

doi:10.1039/c3dt32750g

Cited by 5 publications

(3 citation statements)

References 30 publications

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“…The excited state spectrum for PDI monomer 1 is similar to the IR excited state spectra of other rylene derivatives. 51,52 We note that triptycene has no strong IR bands above 1451 cm −1 , although weak contributions may appear at 1589 and 1598 cm −1 . 53 As triptycene does not participate in the excited state dynamics of the molecules studied here, it should have negligible contribution to the fsIR spectra.…”

Section: ■ Resultsmentioning

confidence: 78%

Characterization of Excimer Relaxation via Femtosecond Shortwave- and Mid-Infrared Spectroscopy

2017

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Excimer formation plays a significant role in trapping excitons within organic molecular solids. Covalent dimers of perylene-3,4:9,10-bis(dicarboximide) (PDI) are useful model systems for studying these processes as their intermolecular geometries can be precisely tuned. Using femtosecond visible-pump infrared-probe (fsIR) spectroscopy in the shortwave- and mid-infrared regions, we characterize two PDI dimers with a cofacial and a slip-stacked geometry that are coupled through a triptycene bridge. In the mid-infrared region, fsIR spectra for the strongly coupled dimers are highly blue-shifted compared to spectra for monomeric PDI. The perylene core stretching modes provide a directly observable probe of excimer relaxation, as they are particularly sensitive to this process, which is associated with a small blue shift of these modes in both dimers. The broad Frenkel-to-CT state electronic transition of the excimer, the edge of which has previously been detected in the NIR region, is now fully resolved to be much broader and to extend well into the shortwave infrared region for both dimers and is likely a generic feature of π-extended aromatic excimers.

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Section: ■ Resultsmentioning

confidence: 78%

Characterization of Excimer Relaxation via Femtosecond Shortwave- and Mid-Infrared Spectroscopy

2017

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“…It is also eminently apparent that the relatively long-lived photoexcited states and the absorptions that can be tuned to span the entire visible spectrum and move well into the nearinfrared pose significant potential for photon-harvesting applications such as in photovoltaics and photocatalysis. Toward this end, we have already shown that these compounds can be employed for photoinduced charge transfer to electron acceptors such as perylene diimides 34 and the semiconducting oxide TiO 2 . 35 Thus, even a half-century after their discovery, M 2 quadruply bonded units still afford some unique properties and avenues for new research.…”

Section: ■ Concluding Remarksmentioning

confidence: 99%

Photophysical Studies of Metal to Ligand Charge Transfer Involving Quadruply Bonded Complexes of Molybdenum and Tungsten

2015

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Photoinduced metal-to-ligand charge transfer transitions afford numerous applications in terms of photon energy harvesting. The majority of metal complexes studied to date involve diamagnetic systems of d(6), d(8), and d(10) transition metals. These typically have very short-lived, ∼100 fs, singlet metal to ligand charge transfer ((1)MLCT) states that undergo intersystem crossing to triplet metal to ligand charge transfer ((3)MLCT) states that are longer lived and are responsible for much of the photophysical studies. In contrast, the metal-metal quadruply bonded complexes of molybdenum and tungsten supported by carboxylate, O2CR, and related amidinate ligands (RN)2C(R') have relatively long-lived (1)MLCT states arising from M2δ to Lπ* transitions. These have lifetimes in the range 1-20 ps prior to intersystem crossing to T1 states that may be (3)MLCT or (3)MMδδ* with lifetimes of 1-100 ns and 1-100 μs, respectively. The M2 quadruply bonded complexes take the form M2L4 or M2L4-nL'n where n = 1-3. Thus, in their photoexcited MLCT states, these compounds pose the question of how the charge resides on the ligands. This Account reviews the current knowledge of how charge is positioned with time in S1 and T1 states with the aid of active IR reported groups located on the ligands, for example, C≡X multiple bonds (X = C, N, or O). Several examples of localized and delocalized charge distributions are noted along with kinetic barriers to the interconversion of MLCT and δδ* states. On the 50th anniversary of the recognition of the MM quadruple bond, these complexes are revealing some remarkable features in the study of the photophysical properties of metal-ligand charge transfer states.

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“…Since the pioneering report of Ford and Kamat, TA spectroscopy continues to be a useful probe of 3 PDI*. − Electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) spectroscopy are powerful techniques for identifying and characterizing triplet states of organic molecules, and their application to 3 PDI* has been demonstrated. − Surprisingly, the vibrational spectroscopy of 3 PDI* is largely unexplored. Among the few studies of PDI excited states by vibrational spectroscopy, − only one has recently identified several IR absorption bands of a triplet excited state . Here, we report resonance Raman spectra of a PDI dimer 1 (Scheme ) in its ground and lowest triplet states.…”

Section: Introductionmentioning

confidence: 99%

Resonance Raman Spectra of a Perylene Bis(dicarboximide) Chromophore in Ground and Lowest Triplet States

2013

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Resonance Raman spectroscopy is employed to probe the ground (S0) and lowest triplet (T1) excited states of a perylene bis(dicarboximide) (PDI) dimer. Four bands at ~1324, 1507, ~1535, and 1597 cm(-1) are signatures of the T1 excited state; a fifth band at ~1160 cm(-1) is tentatively assigned. Density functional calculations of an asymmetrically substituted PDI monomer match the experimental bands of the PDI dimer in both S0 and T1 states. The match supports a T1 excited state that is localized on a single PDI moiety of the dimer. The normal modes of the asymmetrically substituted PDI are correlated with ones calculated for the unsubstituted PDI in the D2h point group. Patterns in the Raman intensities are consistent with an A-term mechanism of enhancement. The positions of six bands are predicted for the resonance Raman spectrum of unsubstituted PDI in its T1 excited state. The spectra and normal-mode analysis reported here are expected to facilitate future studies of singlet fission in PDI crystals or other assemblies.

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Photoinduced charge transfer involving a MoMo quadruply bonded complex to a perylene diimide

Cited by 5 publications

References 30 publications

Characterization of Excimer Relaxation via Femtosecond Shortwave- and Mid-Infrared Spectroscopy

Characterization of Excimer Relaxation via Femtosecond Shortwave- and Mid-Infrared Spectroscopy

Photophysical Studies of Metal to Ligand Charge Transfer Involving Quadruply Bonded Complexes of Molybdenum and Tungsten

Resonance Raman Spectra of a Perylene Bis(dicarboximide) Chromophore in Ground and Lowest Triplet States

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