Direct Observation of Reversible Electronic Energy Transfer Involving an Iridium Center

Denisov, Sergey A.; Cudré, Yanouk; Verwilst, Peter; Jonusauskas, Gediminas; Marín-Suárez, Marta; Fernández-Sánchez, Jorge F.; Baranoff, Etienne; McClenaghan, Nathan D.

doi:10.1021/ic4030712

Cited by 53 publications

(47 citation statements)

References 34 publications

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“…The fitting procedure results in an activation energy (E a ) of ∼1740 cm −1 , on the larger end of the typical range observed in other triplet excited state equilibrated compounds. 21,29,35,45 The τ 1 values also increase with decreasing temperature, although the uncertainty in the higher temperature values of τ 1 did not allow for quantitative fitting. A normalized plot of the corresponding decay rates k 1 , k 2 , and k 3 revealed that k 1 and k 2 have similar temperature-dependent profiles.…”

Section: ■ Experimental Methodsmentioning

confidence: 98%

Excited State Equilibrium Induced Lifetime Extension in a Dinuclear Platinum(II) Complex

2014

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Covalently linking two square planar platinum(II) centers using two pyrazolate bridging ligands allows the filled dz(2) orbitals on each Pt center to overlap, producing a Pt-Pt σ interaction and new low energy dσ* → π* metal-metal-to-ligand charge transfer (MMLCT) transitions terminating on an appropriate π-acceptor ligand such as 2-phenylpyridine (ppy). In an effort to extend the lifetime of the associated MMLCT excited state, we decided to append piperidinyl naphthalimide (PNI) chromophores to the 2-phenylpyridine charge transfer ligands. This structural modification introduces low-lying PNI-based triplet states serving as long-lived triplet population reservoirs, thermally capable of repopulating the charge transfer state at room temperature (RT), thereby extending its excited state lifetime. Specifically, [Pt(PNI-ppy)(μ-Ph2pz)]2 (1), where PNI-ppy is N-(2-phenylpyridine)-4-(1-piperidinyl)naphthalene-1,8-dicarboximide and Ph2pz is 3,5-diphenylpyrazolate, was synthesized and structurally characterized. The static and dynamic photophysical behavior of 1 was directly compared to the MMLCT complex [Pt(ppy)(μ-Ph2pz)]2 (2), lacking the PNI substituents, as well as the naked PNI-ppy ligand 3, intended to independently model the MMLCT and NI excited state properties, respectively. Ultimately, experimental evidence for the presence of both the (3)PNI and (3)MMLCT excited states in 1 were revealed at RT in nanosecond transient absorbance and time-resolved photoluminescence spectroscopy, respectively. Temperature-dependent transient absorption spectroscopy permitted the extraction of an energy gap of 1740 cm(-1) between the MMLCT and PNI triplet states in 1 along with the time constants associated with the interconversions between the various excited states resident on this complex chromophore, ultimately decaying back to the ground state with a time constant of 65 μs at RT.

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Section: ■ Experimental Methodsmentioning

confidence: 98%

Excited State Equilibrium Induced Lifetime Extension in a Dinuclear Platinum(II) Complex

2014

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“…Similar to the design of Ir‐7 , a bichromophoric biscyclometalated iridium complex was reported by McClenaghan et al in which a pyrene unit was attached to an auxiliary bpy ligand of the complex via a short ethylene spacer . The photophysical properties of the complex was studied with steady‐state and time‐resolved spectroscopies, and a reversible intramolecular energy transfer was also proven established within this molecule.…”

Section: Bichromophoric Transition‐metal Complex Sensitizersmentioning

confidence: 71%

New Bichromophoric Triplet Photosensitizer Designs and Their Application in Triplet–Triplet Annihilation Upconversion

Guo

Liu

Chen

et al. 2018

Advanced Optical Materials

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the distinctive advantage of using noncoherent light as the excitation source. Hence, the TTA-based photon upconversion (UC) is promised with a wider range of applications, such as harvesting the much abundant low-energy photons in the solar spectral irradiation and converting them to usable photons in photovoltaic devices. [4,5] Moreover, the development of TTA UC is also driven by the potential applications pertinent to photocatalysis and bio-technologies. [6][7][8][9] The two main functional components in a TTA UC system are the triplet photosensitizer and annihilator, the latter of which also serves as the emitter. While only a limited number of annihilators have so far been identified capable of efficient TTA upconverted emission, remarkable progress has been made with the design and investigation of photosensitizers in the past decade. A range of transitionmetal complexes and organic structures have been studied as potent photosensitizers. By virtue of all the various sensitizers that have been developed, a wide range of photon energy, ranging from visible to near-infrared, can now be used and upconverted by the TTA systems reported in the literature. [10,11] Furthermore, different types of materials, including various solvents, gels, polymers, have been employed as matrices to perform TTA UC, and even matrix-free conditions have been reported. [11][12][13][14][15] Mechanism of TTA UCThe streamlined mechanistic steps in a TTA UC are summarized in Figure 1. [16] In a typical bi-component system, upon absorbing a low-energy photon, the photosensitizer is excited into a singlet excited state before undergoing inter-system crossing (ISC) to the triplet state. Then, an intermolecular triplet-triplet energy transfer (TTET) takes place between the excited sensitizer and a nearby annihilator, regenerating the ground-state sensitizer along with an annihilator triplet. Since the annihilators are usually organic hydrocarbon molecules with spin-forbidden triplet-to-singlet relaxations, long-lived annihilator triplets thus accumulate over time, until bimolecular triplet-triplet annihilation takes place and generates a As indispensable molecular components, photosensitizers play a crucial role in determining the quantum efficiency of triplet-triplet annihilation upconversion (TTA UC). This emergent technology has attracted great attention in recent years for realizing large anti-Stokes shifts with noncoherent excitation sources. In a typical TTA UC, low-energy photons are first harvested by the photosensitizers, which upon intersystem crossing (ISC) undergo triplettriplet energy transfer (TTET) to emitters (i.e., annihilators). Following the bimolecular TTA among the emitters, high-energy photons are given off by the singlet excited state of the emitters. Apparently, the efficiencies of photon absorption, ISC, and TTET are all dependent on the sensitizers. With a Dextertype ET mechanism requiring collisional interactions, a long triplet lifetime of the energy donor (photosensitizer) is evidently favorable for enhancing ...

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“…In solutiona nd host matrices (a polymericP S3 98 membrane and an anostructured metal oxide matrix (AP200/19)), remarkably higho xygen sensitivity is observed. [24] Some bis-cyclometalated Ir III complexes (15 and 16)w ith the general formula Ir(1-phenylpyrazole) 2 (X^NPyrene), where X^NPyrene represent synthetically easily accessible bidentate chelate with X = No rO ,w erea lso reported. [25] Even subtle modifications on the pyrene-containing ligand dramatically affected the observed emission lifetimesi nt he range 0.33 to 104 ms.…”

Section: à5mentioning

confidence: 99%

Harnessing Reversible Electronic Energy Transfer: From Molecular Dyads to Molecular Machines

Denisov

Pozzo

et al. 2016

ChemPhysChem

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Reversible electronic energy transfer (REET) may be instilled in bi‐/multichromophoric molecule‐based systems, following photoexcitation, upon judicious structural integration of matched chromophores. This leads to a new set of photophysical properties for the ensemble, which can be fully characterized by steady‐state and time‐resolved spectroscopic methods. Herein, we take a comprehensive look at progress in the development of this type of supermolecule in the last five years, which has seen systems evolve from covalently tethered dyads to synthetic molecular machines, exemplified by two different pseudorotaxanes. Indeed, REET holds promise in the control of movement in molecular machines, their assembly/disassembly, as well as in charge separation.

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Direct Observation of Reversible Electronic Energy Transfer Involving an Iridium Center

Cited by 53 publications

References 34 publications

Excited State Equilibrium Induced Lifetime Extension in a Dinuclear Platinum(II) Complex

Excited State Equilibrium Induced Lifetime Extension in a Dinuclear Platinum(II) Complex

New Bichromophoric Triplet Photosensitizer Designs and Their Application in Triplet–Triplet Annihilation Upconversion

Harnessing Reversible Electronic Energy Transfer: From Molecular Dyads to Molecular Machines

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