RhI dimers with bridging aryl isocyanide and di-phosphine ligands show NIR-I or NIR-II fluorescence/phosphorescence, depending on the ligands and conformational rigidity at the Rh2 core. Rh-Rh intera...

The total spin of a metal center can be switched in different ways. In this concept, the phenomenon spin crossover is compared with coordination-induced spin-state switching. The impact of the switch....

Halogenation of ligands intensely modulates the redox and photophysical properties of transition-metal complexes, yet fully halogenated systems remain largely unexplored. Here we report the synthesis ...

Visible photons carry significantly more energy than the thermal energies typically used to overcome activation barriers in conventional chemistry. This thermodynamic advantage enables photochemical reactions that are inaccessible from electronic ground states. However, photochemistry also faces a kinetic challenge: excited states are inherently short-lived, necessitating rapid reactivity before their decay. In this Outlook, we explore the unique interplay of thermodynamics and kinetics in molecular photochemistry. We highlight current limits and knowledge gaps and propose directions for advancing the conceptual framework of photocatalysis. Topics include the design of photocatalysts with extreme redox potentials, the use of solvated electrons and visible-to-UV upconversion, and the potential to bypass Kasha’s rule for higher-energy photochemical processes. Our aim is to survey strategies for pushing the boundaries of photocatalysis and to inspire future conceptual innovation in the field.

Strategic ligand engineering is essential for the development of new photoactive transition metal complexes. One such application is the control of supramolecular, one-dimensional stacking of square-planar d8-organometallic systems. Here, we report the synthesis of a macrocyclic, tetradentate isocyanide ligand, CN4, and facile coordination to rhodium(I) yielding [Rh(CN4)][BArF4]. Single-crystal X-ray diffraction upon acetone-solution grown crystals reveals formation of a tetrameric RhI stack, constructed of two dimeric forms of monomers. UV–visible absorption spectroscopy shows two prominent absorption bands, assigned to dimer (525 nm) and tetramer (840 nm), confirming stacked species. These assignments are further supported by DOSY measurements. Solvent control over this equilibrium is achieved first with acetonitrile, favoring only tetrameric aggregation, and also with dichloromethane, disabling aggregation completely. Upon excitation, the monomeric form returns to its electronic ground state in less than 10 ns. The near-infrared-absorbing tetramer exhibits an excited state with a lifetime of 150 ns in deaerated acetonitrile and NIR-II emission at 1040 nm. This discovery provides new opportunities for innovation in photophysics and photochemistry through polynuclear architectures that exhibit emergent properties compared to traditional mononuclear transition metal complexes.

Classical upconversion employs sensitizers and annihilators as two distinct molecular species and is, therefore, classified as heteromolecular. Homomolecular upconversion, the unification of both role...

Transition-metal complexes featuring metal-centered excited states have recently emerged as mechanistically distinct platforms for selective photochemistry, including photoredox catalysis. Among these...

The light-induced separation of charges, fundamental to natural photosynthesis, is key to converting solar energy into chemical energy in artificial systems. One challenge is that charges tend to spon...

Beilstein Journal of Organic Chemistry

The photoinduced accumulation of redox equivalents is a challenging requirement for artificial photosynthesis. Now a molecule has been developed in which the sequential absorption of photons results in the temporary accumulation of two holes and two electrons. The employed strategy opens up new possibilities for charge accumulation under low photon densities.

The photoinduced accumulation of redox equivalents is a challenging requirement for artificial photosynthesis. Now a molecule has been developed in which the sequential absorption of photons results i...

A research team from the University of Basel has developed a new molecule modeled on plant photosynthesis: under the influence of light, it stores two positive and two negative charges at the same tim...

The reduction potentials of electronically excited states are crucial input values for photoredox reaction design. Since they are not directly measurable, they are typically estimated from the corresp...

While perfluorinated isocyanide ligands such as CNCF3 and CNC6F5 have been known for decades, their use by organometallic chemists has been limited primarily due to the challenges associated with their cumbersome synthesis. In this study, we present an improved synthetic route to [Cr(CO)5(CNC6F5)] and present its structural characterization. For a set of isocyanide ligands (CNC6H5, p-CNC6H4F, CNCH3) and their perfluorinated counterparts (CNC6F5, CNCF3), Gibbs energies of complexation have been calculated with regard to a series of isoelectronic metal fragments [V(CO)5]−, [Cr(CO)5], [Mn(CO)5]+, and [Fe(CO)5]2+. Furthermore, the σ-donor and π-acceptor properties of these isocyanide ligands in the resulting complexes were analyzed using the EDA-NOCV method. For completeness, we have also included ligands such as CO, CNH, and N2 into the analysis. While only minor differences in complexation energies are observed for the Cr(CO)5 fragment, more pronounced effects have been observed for the charged complexes. Interestingly, perfluorinated isocyanide ligands show in all cases higher complexation energies than the carbonyl ligands, indicating their strong binding to metal centers. Their pronounced σ-donor and π-acceptor abilities reveal their potential suitability to stabilize metal centers in both positive and negative oxidation states.

CoIII complexes have recently become an important focus in photophysics and photoredox catalysis due to metal-centered excited states with strong oxidizing properties. Optimizing chelate ligand bite a...

Photoactive CrIII complexes are typically based on polypyridine coordination environments, exhibit red luminescence, and are good photo-oxidants but have modest photoreducing properties. We report new...

Nearly all photochemical transformations known to date follow Kasha’s rule, implying that reactions occur only from the lowest electronically excited state of a given spin multiplicity due to the fast...

A high-sensitivity, broadband, transient, full-Stokes spectroscopy setup is demonstrated, which can detect quickly varying small signals from chiral emitters.

Ligand-to-metal charge transfer photocatalysts (LMCT PCs) are being increasingly implemented towards construction and functionalization of organic molecules. Leveraging photoinduced metal-ligand bond ...

Ruthenium and iridium are key components in the most important applications of photoactive complexes, namely, light-emitting devices, photocatalysis, bioimaging, biosensing, and photodynamic therapy. ...

The response of a solvation shell to molecular solute photoexcitation is an ubiquitous phenomenon of great relevance in chemistry. This response can occur within just few tens of femtoseconds, making ...

Luminescence and photochemistry involve electronically excited states that are inherently unstable and therefore spontaneously decay to electronic ground states, in most cases by nonradiative energy release that generates heat. This energy dissipation can occur on a time scale of 100 fs (∼10–13 s) and usually needs to be slowed down to at least the nanosecond (∼10–9 s) time scale for luminescence and intermolecular photochemistry to occur. This is a challenging task with many different factors to consider. An alternative emerging strategy is to target dissociative excited states that lead to metal–ligand bond homolysis on the subnanosecond time scale to access synthetically useful radicals. Based on a thorough review at the most recent advances in the field, this article aims to provide a concise guide to obtaining luminescent and photochemically useful coordination compounds with d-block elements. We hope to encourage “photo-motivated” chemists who have been reluctant to apply their synthetic and other knowledge to photophysics and photochemistry, and we intend to stimulate new approaches to the synthetic control of excited state behavior.

Luminescence and photochemistry involve electronically excited states that are inherently unstable and therefore spontaneously decay to electronic ground states, in most cases by nonradiative energy release that generates heat. This energy dissipation can occur on a time scale of 100 fs (∼10–13 s) and usually needs to be slowed down to at least the nanosecond (∼10–9 s) time scale for luminescence and intermolecular photochemistry to occur. This is a challenging task with many different factors to consider. An alternative emerging strategy is to target dissociative excited states that lead to metal–ligand bond homolysis on the subnanosecond time scale to access synthetically useful radicals. Based on a thorough review at the most recent advances in the field, this article aims to provide a concise guide to obtaining luminescent and photochemically useful coordination compounds with d-block elements. We hope to encourage “photo-motivated” chemists who have been reluctant to apply their synthetic and other knowledge to photophysics and photochemistry, and we intend to stimulate new approaches to the synthetic control of excited state behavior.

Iron is the most abundant transition metal element and would be the ideal replacement for noble metals in many applications that rely on luminescent and long-lived electronically excited states. We sh...

Iron is the most abundant transition metal element and would be the ideal replacement for noble metals in many applications that rely on luminescent and long-lived electronically excited states. We sh...

Ultrafast IR absorption spectroscopy was utilized to interrogate excited-state electron transfer in a strongly-coupled, cyanide-bridged photoinduced mixed-valent system. Despite structural asymmetry,...

Many important synthetic-oriented works have proposed excited organic radicals as photoactive species, yet mechanistic studies raised doubts about whether they can truly function as photocatalysts. This skepticism originates from the formation of (photo)redox-active degradation products and the picosecond decay of electronically excited radicals, which is considered too short for diffusion-based photoinduced electron transfer reactions. From this perspective, we analyze important synthetic transformations where organic radicals have been proposed as photocatalysts, comparing their theoretical maximum excited state potentials with the potentials required for the observed photocatalytic reactivity. We summarize mechanistic studies of structurally similar photocatalysts indicating different reaction pathways for some catalytic systems, addressing cases where the proposed radical photocatalysts exceed their theoretical maximum reactivity. Additionally, we perform a kinetic analysis to explain the photoinduced electron transfer observed in excited radicals on subpicosecond time scales. We further rationalize the potential anti-Kasha reactivity from higher excited states with femtosecond lifetimes, highlighting how future photocatalysis advancements could unlock new photochemical pathways.