Photophysical Studies of a Zr(IV) Complex with Two Pyrrolide-Based Tetradentate Schiff Base Ligands.

The reaction of two equivalents of ,-bis(2-pyrrolylmethylidene)-1,2-phenylenediamine (Hbppda) with tetrabenzylzirconium provided the air- and moisture-stable eight-coordinate complex Zr(bppda). Temperature-dependent steady-state and time-resolved emission spectroscopy established weak photoluminescence (Φ = 0.4% at 293 K) by a combination of prompt fluorescence and thermally activated delayed fluorescence (TADF) upon visible light excitation at and around room temperature.

Elucidating the mechanism of photochemical CO reduction to CO using a cyanide-bridged di-manganese complex.

The complex, [{[Mn(bpy)(CO)]}(μ-CN)] (Mn2CN+), has previously been shown to photochemically reduce CO to CO. The detailed mechanism behind its reactivity was not elucidated. Herein, the photoevolution of this reaction is studied in acetonitrile (MeCN) using IR and UV-vis spectroscopy.

Long-Lived Photoluminescence of Molecular Group 14 Compounds through Thermally Activated Delayed Fluorescence.

Photoluminescent molecules exploiting the sizable spin-orbit coupling constants of main group metals and metalloids to access long-lived triplet excited states are relatively rare compared to phosphorescent transition metal complexes. Here we report the synthesis of three air- and moisture-stable group 14 compounds E(PDP), where E = Si, Ge, or Sn and [PDP] is the doubly deprotonated form of 2,6-bis(5-methyl-3-phenyl-1-pyrrol-2-yl)pyridine. In solution, all three molecules exhibit exceptionally long-lived triplet excited states with lifetimes in the millisecond range and show highly efficient photoluminescence (Φ ≤ 0.

Vibronic and excitonic dynamics in perylenediimide dimers and tetramer.

Broad-band pump-probe spectroscopy combined with global and target analysis is employed to study the vibronic and excitonic dynamics of two dimers and a tetramer of perylenediimides. A simultaneous analysis is developed for two systems that have been measured in the same conditions. This enhances the resolvability of the vibronic and excitonic dynamics of the systems, and the solvent contributions that are common in the experiments.

Energy Migration Processes in Re(I) MLCT Complexes Featuring a Chromophoric Ancillary Ligand.

We present the synthesis, structural characterization, electronic structure calculations, and ultrafast and supra-nanosecond photophysical properties of a series of five Re(I) bichromophores exhibiting metal to ligand charge transfer (MLCT) excited states based on the general formula -[Re(NN)(CO)(PNI-py)]PF where PNI-py is 4-piperidinyl-1,8-naphthalimidepyridine and NN is a diimine ligand (-), along with their corresponding model chromophores where 4-ethylpyridine was substituted for PNI-py (-). The diimine ligands used include 1,10-phenanthroline (phen, ), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bcp, ), 4,4'-di--butyl-2,2'-bipyridine (dtbb, ), 4,4'-diethyl ester-2,2'-bipyridine (deeb, ), and 2,2'-biquinoline (biq, ). In these metal-organic bichromophores, structural modification of the diimine ligand resulted in substantial changes to the observed energy transfer efficiencies between the two chromophores as a result of the variation in MLCT excited-state energies.

Delayed fluorescence from a zirconium(IV) photosensitizer with ligand-to-metal charge-transfer excited states.

Advances in chemical control of the photophysical properties of transition-metal complexes are revolutionizing a wide range of technologies, particularly photocatalysis and light-emitting diodes, but they rely heavily on molecules containing precious metals such as ruthenium and iridium. Although the application of earth-abundant 'early' transition metals in photosensitizers is clearly advantageous, a detailed understanding of excited states with ligand-to-metal charge transfer (LMCT) character is paramount to account for their distinct electron configurations. Here we report an air- and moisture-stable, visible light-absorbing Zr(IV) photosensitizer, Zr(PDP), where [PDP] is the doubly deprotonated form of [2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine].

Reduction-induced CO dissociation by a [Mn(bpy)(CO)][SbF] complex and its relevance in electrocatalytic CO reduction.

[Mn(bpy)(CO)3Br] is recognized as a benchmark electrocatalyst for CO2 reduction to CO, with the doubly reduced [Mn(bpy)(CO)3]- proposed to be the active species in the catalytic mechanism. The reaction of this intermediate with CO2 and two protons is expected to produce the tetracarbonyl cation, [Mn(bpy)(CO)4]+, thereby closing the catalytic cycle. However, this species has not been experimentally observed.

A cyanide-bridged di-manganese carbonyl complex that photochemically reduces CO to CO.

Manganese(i) tricarbonyl complexes such as [Mn(bpy)(CO)3L] (L = Br, or CN) are known to be electrocatalysts for CO2 reduction to CO. However, due to their rapid photodegradation under UV and visible light, these monomeric manganese complexes have not been considered as photocatalysts for CO2 reduction without the use of a photosensitizer. In this paper, we report a cyanide-bridged di-manganese complex, {[Mn(bpy)(CO)3]2(μ-CN)}ClO4, which is both electrocatalytic and photochemically active for CO2 reduction to CO.

Triplet Energy Transfer Governs the Dissociation of the Correlated Triplet Pair in Exothermic Singlet Fission.

Singlet fission is a spin-allowed process of exciton multiplication that has the potential to enhance the efficiency of photovoltaic devices. The majority of studies to date have emphasized understanding the first step of singlet fission, where the correlated triplet pair is produced. Here, we examine separation of correlated triplet pairs.

A Zirconium Photosensitizer with a Long-Lived Excited State: Mechanistic Insight into Photoinduced Single-Electron Transfer.

Time-resolved emission spectroscopy for the luminescent zirconium complex Zr(PDP) (PDP = 2,6-bis(5-methyl-3-phenyl-1 H-pyrrol-2-yl)pyridine) revealed a long-lived excited state with a lifetime τ = 325 ± 10 μs. Computational studies using time-dependent density functional theory were conducted to identify the nature of the luminescent excited state as a mixed triplet intraligand/ligand-to-metal charge-transfer state. Stern-Volmer experiments showed a strong dependence of the quenching rate on the redox potential of the quencher indicating photoinduced single-electron transfer (SET) as the quenching pathway.

Exciton delocalization drives rapid singlet fission in nanoparticles of acene derivatives.

We compare the singlet fission dynamics of five pentacene derivatives precipitated to form nanoparticles. Two nanoparticle types were distinguished by differences in their solid-state order and kinetics of triplet formation. Nanoparticles that comprise primarily weakly coupled chromophores lack the bulk structural order of the single crystal and exhibit nonexponential triplet formation kinetics (Type I), while nanoparticles that comprise primarily more strongly coupled chromophores exhibit order resembling that of the bulk crystal and triplet formation kinetics associated with the intrinsic singlet fission rates (Type II).