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Coherence in chemistry: Foundations and frontiers
(American Chemical Society, 2024-11-13)
Coherence refers to correlations in waves. Because matter has a wave-particle nature, it is unsurprising that coherence has deep connections with the most contemporary issues in chemistry research (e.g., energy harvesting, femtosecond spectroscopy, molecular qubits and more). But what does the word “coherence” really mean in the context of molecules and other quantum systems? We provide a review of key concepts, definitions, and methodologies, surrounding coherence phenomena in chemistry, and we describe how the terms “coherence” and “quantum coherence” refer to many different phenomena in chemistry. Moreover, we show how these notions are related to the concept of an interference pattern. Coherence phenomena are indeed complex, and ambiguous definitions may spawn confusion. By describing the many definitions and contexts for coherence in the molecular sciences, we aim to enhance understanding and communication in this broad and active area of chemistry.
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Seeking a quantum advantage with trapped-ion quantum simulations of condensed-phase chemical dynamics
(Nature Research, 2024-05-01)
Simulating the quantum dynamics of molecules in the condensed phase represents a longstanding challenge in chemistry. Trapped-ion quantum systems may serve as a platform for the analog-quantum simulation of chemical dynamics that is beyond the reach of current classical-digital simulation. To identify a ‘quantum advantage’ for these simulations, performance analysis of both analog-quantum simulation on noisy hardware and classical-digital algorithms is needed. In this Review, we make a comparison between a noisy analog trapped-ion simulator and a few choice classical-digital methods on simulating the dynamics of a model molecular Hamiltonian with linear vibronic coupling. We describe several simple Hamiltonians that are commonly used to model molecular systems, which can be simulated with existing or emerging trapped-ion hardware. These Hamiltonians may serve as stepping stones towards the use of trapped-ion simulators for systems beyond the reach of classical-digital methods. Finally, we identify dynamical regimes in which classical-digital simulations seem to have the weakest performance with respect to analog-quantum simulations. These regimes may provide the lowest hanging fruit to make the most of potential quantum advantages. (Figure presented.)
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Seeking a Quantum Advantage with Trapped-Ion Quantum Simulations of Condensed-Phase Chemical Dynamics
(Cornell University, 2023-05-04)
Simulating the quantum dynamics of molecules in the condensed phase represents a longstanding challenge in chemistry. Trapped-ion quantum systems may serve as a platform for the analog-quantum simulation of chemical dynamics that is beyond the reach of current classical-digital simulation. To identify a 'quantum advantage' for these simulations, performance analysis of both analog-quantum simulation on noisy hardware and classical-digital algorithms is needed. In this Review, we make a comparison between a noisy analog trapped-ion simulator and a few choice classical-digital methods on simulating the dynamics of a model molecular Hamiltonian with linear vibronic coupling. We describe several simple Hamiltonians that are commonly used to model molecular systems, which can be simulated with existing or emerging trapped-ion hardware. These Hamiltonians may serve as stepping stones toward the use of trapped-ion simulators for systems beyond the reach of classical-digital methods. Finally, we identify dynamical regimes where classical-digital simulations seem to have the weakest performance compared to analog-quantum simulations. These regimes may provide the lowest hanging fruit to exploit potential quantum advantages.
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Ultrafast Electron Dynamics of a Ferrocene-Based Butadiyne-Bridged Complex
(American Chemical Society, 2026-03-26)
High Resolution Image Download MS PowerPoint Slide Photoinduced electron transfer (ET) in alkyne-linked donor–bridge–acceptor (DBA) compounds is strongly influenced by torsional flexibility, allowing control over ET without altering the donor–acceptor distance. Here, we investigate excited-state dynamics in Fc-C4-NAP, a DBA compound featuring a ferrocene (Fc) donor, a butadiyne bridge (C4), and a 1,8-naphthalimide (NAP) acceptor. Unlike analogues DBA compounds with fully organic planar donors, Fc-C4-NAP exhibits a complex excited-state manifold. Femtosecond transient absorption (TA) measurements in the visible and mid-IR regions found three characteristic relaxation times (0.3–0.5 ps, ∼2.6 ps, and 17–20 ps) following its excitation at 402 nm, which prepares NAP-centered excited states.TD-DFT computations indicate that the acceptor-based locally excited (LE) and the charge separated (CS) diabatic states are well coupled to the Fc states associated with d-states of Fe. This bridge-mediated coupling, estimated at 200–500 cm –1, is strong enough to induce significant mixing of the diabatic states, which also depends strongly on the torsional angle between the NAP and the C4-bonded cyclopentadienyl ring. The spectral changes observed in the TA experiments suggest that the fast component of 0.3–0.5 ps reflects the lifetime of the bright, dominantly NAP-centered state, which relaxes predominantly to the Fc-based states. The middle component of 2.6 ps could have multiple contributions, including relaxation of the nominal CS state, vibrational cooling, and solvation. The slow decay component of ca. 20 ps corresponds to the lifetime of the lowest-energy Fc states; two Fc states of similar energies but perpendicular polarizations. The complex nature of the eigenstates, unraveled by TD-DFT analysis, results in efficient competition of the energy transfer process to the Fc-based excited states with the CS process. These results highlight the key role played by diabatic state coupling, conformational dynamics, and Fc d-orbitals in shaping the ultrafast dynamics of Fc-based DBA systems, guiding the future design of photoactive materials for solar energy and molecular electronics applications.
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Photo-induced electron transfer dynamics and its mid-IR modulation of an ethyne bridged donor-acceptor complex
(Royal Society of Chemistry, 2025-10-02)
Electron transfer (ET) rate in donor–bridge–acceptor (DBA) complexes is modulated by the alkyne bridge vibrational excitation. Torsion angle ( θ ) offers selectivity in accessing locally-excited, acceptor-centered (S 2 ) state of the DBA complex.
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