Red-Light-Induced Ligand-to-Metal Charge Transfer Catalysis by Tuning the Axial Coordination of Cobyrinate.

Photoinduced ligand-to-metal charge transfer (LMCT) is a powerful technique for the formation of reactive radical species via homolytic cleavage of the metal-ligand bond. Here, we present that the excited state LMCT of a cobyrinate complex can be accessed by tuning its axial coordination with thiolates as ligands. We demonstrate the photoreduction of cobalt via the excited state Co-S bond homolytic cleavage, as guided by the DFT calculations, which signify the relevance of thiolate axial ligands facilitating the LMCT reactivity.

The development and applications of multidimensional biomolecular spectroscopy illustrated by photosynthetic light harvesting.

The parallel and synergistic developments of atomic resolution structural information, new spectroscopic methods, their underpinning formalism, and the application of sophisticated theoretical methods have led to a step function change in our understanding of photosynthetic light harvesting, the process by which photosynthetic organisms collect solar energy and supply it to their reaction centers to initiate the chemistry of photosynthesis. The new spectroscopic methods, in particular multidimensional spectroscopies, have enabled a transition from recording rates of processes to focusing on mechanism. We discuss two ultrafast spectroscopies - two-dimensional electronic spectroscopy and two-dimensional electronic-vibrational spectroscopy - and illustrate their development through the lens of photosynthetic light harvesting.

Photodriven Ammonia Synthesis from Manganese Nitrides: Photophysics and Mechanistic Investigations.

Ammonia synthesis from N,N,O,O-supported manganese(V) nitrides and 9,10-dihydroacridine using proton-coupled electron transfer and visible light irradiation in the absence of precious metal photocatalysts is described. While the reactivity of the nitride correlated with increased absorption of blue light, excited-state lifetimes determined by transient absorption were on the order of picoseconds. This eliminated excited-state manganese nitrides as responsible for bimolecular N-H bond formation.

Quantum State Combinatorics.

This paper concerns the analysis of large quantum states. It is a notoriously difficult problem to quantify separability of quantum states, and for large quantum states, it is unfeasible. Here we posit that when quantum states are large, we can deduce reasonable expectations for the complex structure of non-classical multipartite correlations with surprisingly little information about the state.

Discovery of Multiple Light-Harvesting States of the Photosynthetic Protein PE545.

Cryptophytes are photosynthetic microalga that flourish in a remarkable diversity of natural environments by using pigment-containing proteins with absorption maxima tuned to each ecological niche. While this diversity in the absorption has been well established, the subsequent photophysics is highly sensitive to the local protein environment and so may exhibit similar variation. Thermal fluctuations of the protein conformation are expected to introduce photophysical heterogeneity of the pigments that may have evolved important functional properties in a manner similar to that of the absorption.

From Coherence to Function: Exploring the Connection in Chemical Systems.

ConspectusThe role of quantum mechanical coherences or coherent superposition states in excited state processes has received considerable attention in the last two decades largely due to advancements in ultrafast laser spectroscopy. These coherence effects hold promise for enhancing the efficiency and robustness of functionally relevant processes, even when confronted with energy disorder and environmental fluctuations. Understanding coherence deeply drives us to unravel mechanisms and dynamics controlled by order and synchronization at a quantum mechanical level, envisioning optical control of coherence to enhance functions or create new ones in molecular and material systems.

Chirped Laser Pulse Control of Vibronic Wavepackets and Energy Transfer in Phycocyanin 645.

Photosynthetic organisms use light-harvesting complexes to increase the spectrum of light that they absorb from solar photons. Recent ultrafast spectroscopic studies have revealed that efficient (sub-ps) energy transfer is mediated by vibronic coherence in the phycobiliprotein phycocyanin 645 (PC645). Here, we report studies that employ broadband pump-probe spectroscopy with linearly chirped excitation pulses to further investigate the relationship between vibronic state preparation and energy transfer dynamics in PC645.

Exciton polaron formation and hot-carrier relaxation in rigid Dion-Jacobson-type two-dimensional perovskites.

The efficiency of two-dimensional Dion-Jacobson-type materials relies on the complex interplay between electronic and lattice dynamics; however, questions remain about the functional role of exciton-phonon interactions. Here we establish the robust polaronic nature of the excitons in these materials at room temperature by combining ultrafast spectroscopy and electronic structure calculations. We show that polaronic distortion is associated with low-frequency (30-60 cm) lead iodide octahedral lattice motions.

Vibronic Coupling Drives the Ultrafast Internal Conversion in a Functionalized Free-Base Porphyrin.

Internal conversion (IC) is a common radiationless transition in polyatomic molecules. Theory predicts that molecular vibrations assist IC between excited states, and ultrafast experiments can provide insight into their structure-function relationship. Here we elucidate the dynamics of the vibrational modes driving the IC process within the Q band of a functionalized porphyrin molecule.

Foundations of Quantum Information for Physical Chemistry.

Quantum information, a field in which great advances have been made in the past decades, now presents opportunities for advanced chemistry. One roadblock to progress, especially for experimental chemical science, is that new concepts and technical definitions need to be learned. In this paper, we review some basic, but sometimes misunderstood, concepts of quantum information based on the mathematical formulation of quantum mechanics that will be useful for chemists interested in discovering ways that chemistry can contribute to the quantum information field.

Molecular Photothermal Conversion Catalyst Promotes Photocontrolled Atom Transfer Radical Polymerization.

Photothermal conversion is a growing research area that promotes thermal transformations with visible light irradiation. However, few examples of dual photothermal conversion and catalysis limit the power of this phenomenon. Here, we take inspiration from nature's ability to use porphyrinic compounds for nonradiative relaxation to convert light into heat to facilitate thermal polymerization catalysis.

Molecular and Supramolecular Materials: From Light-Harvesting to Quantum Information Science and Technology.

The past two decades have witnessed immense advances in quantum information technology (QIT), benefited by advances in physics, chemistry, biology, and materials science and engineering. It is intriguing to consider whether these diverse molecular and supramolecular structures and materials, partially inspired by quantum effects as observed in sophisticated biological systems such as light-harvesting complexes in photosynthesis and the magnetic compass of migratory birds, might play a role in future QIT. If so, how? Herein, we review materials and specify the relationship between structures and quantum properties, and we identify the challenges and limitations that have restricted the intersection of QIT and chemical materials.

Vibrational Dipole-Dipole Coupling and Long-Range Forces between Macromolecules.

Long-range interactions between biomacromolecules are considered important for directing intracellular processes. Recent studies have posited that interactions between oscillating dipoles are well-suited to mediating long-range forces because they are weakly screened by a dielectric environment. Here, we extend these studies and present a quantum electrodynamic mechanism for resonant interactions between vibrational transition dipole moments of molecules.

Extension of molecules with an inverted singlet-triplet gap with conjugated branches to alter the oscillator strength.

Molecules that violate Hund's rule and possess negative singlet-triplet gaps (Δ) have been actively studied for their potential usage in organic light emitting diodes without the need for thermal activation. However, the weak oscillator strength from the symmetry of such molecules has been recognized as their shortcoming for their application in optoelectronic devices. A group of molecules with a common structural motif involving the original molecule with an inverted gap having branches consisting of conjugated molecules of varied structures and extent of conjugation have been predicted to have desirable oscillator strength, but only few detailed and comprehensive studies regarding the form of excited states and the reason behind the improved oscillator strength have been carried out.

Visible light-induced palladium-carbon bond weakening in catalytically relevant T-shaped complexes.

Triggering one-electron redox processes during palladium catalysis holds the potential to unlock new reaction mechanisms and synthetic methods not previously accessible in the typical two-electron reaction manifolds that dominate palladium catalysis. We report that T-shaped organopalladium(ii) complexes coordinated by a bulky monophosphine, a class of organometallic intermediate featured in a range of contemporary catalytic reactions, undergo blue light-promoted bond weakening leading to mild and efficient homolytic cleavage of strong Pd(ii)-C(sp) bonds under ambient conditions. The origin of light-triggered radical formation in these systems, which lack an obvious ligand-based chromophore (, π-systems), was investigated using a combination of DFT calculations, photoactinometry, and transient absorption spectroscopy.

Evidence of a Distinctive Enantioselective Binding Mode for the Photoinduced Radical Cyclization of α-Chloroamides in Ene-Reductases.

We demonstrate here through molecular simulations and mutational studies the origin of the enantioselectivity in the photoinduced radical cyclization of α-chloroacetamides catalyzed by ene-reductases, in particular the ene-reductase and the Old Yellow Enzyme 1, which show opposite enantioselectivity. Our results reveal that neither the π-facial selectivity model nor a protein-induced selective stabilization of the transition states is able to explain the enantioselectivity of the radical cyclization in the studied flavoenzymes. We propose a new enantioinduction scenario according to which enantioselectivity is indeed controlled by transition-state stability; however, the relative stability of the prochiral transition states is not determined by direct interaction with the protein but is rather dependent on an inherent degree of freedom within the substrate itself.

Large Coherent States Formed from Disordered -Regular Random Graphs.

The present work is motivated by the need for robust, large-scale coherent states that can play possible roles as quantum resources. A challenge is that large, complex systems tend to be fragile. However, emergent phenomena in classical systems tend to become more robust with scale.

Manipulation of Charge Delocalization in a Bulk Heterojunction Material Using a Mid-Infrared Push Pulse.

In organic bulk heterojunction materials, charge delocalization has been proposed to play a vital role in the generation of free carriers by effectively reducing the Coulomb attraction via an interfacial charge transfer exciton (CTX). Pump-push-probe (PPP) experiments produced evidence that the excess energy given by a push pulse enhances delocalization, thereby increasing photocurrent. However, previous studies have employed near-infrared push pulses in the range ∼0.

All Lit Up: Exploring the Photophysical Properties of Protein Polymers.

Microtubules and actin filaments are protein polymers that play a variety of energy conversion roles in the biological cell. While these polymers are being increasingly harnessed for mechanochemical roles both inside and outside physiological conditions, their capabilities for photonic energy conversion are not well understood. In this Perspective, we first introduce the reader to the photophysical properties of protein polymers, examining light harvesting by their constituent aromatic residues.

Waveguided energy transfer in pseudo-two-dimensional systems.

Resonance energy transfer (RET) is an important and ubiquitous process whereby energy is transferred from a donor chromophore to an acceptor chromophore without contact via Coulombic coupling. There have been a number of recent advances exploiting the quantum electrodynamics (QED) framework for RET. Here, we extend the QED RET theory to investigate whether real photon exchange can allow for excitation transfer over very long distances if the exchanged photon is waveguided.