Comparison of structural dynamics and coherence of d-d and MLCT light-induced spin state trapping.

Light-induced excited spin state trapping (LIESST) in FeII spin-crossover systems is a process that involves the switching of molecules from low (LS, S = 0) to high spin (HS, S = 2) states. The direct LS-to-HS conversion is forbidden by selection rules, and LIESST involves intermediate states such as 1,3MLCT or 1,3T. The intersystem crossing sequence results in an HS state, structurally trapped by metal-ligand bond elongation through the coherent activation and damping of molecular breathing. The ultrafast dynamics of this process has been investigated in FeN6 ligand field systems, under MLCT excitation. Herein, we studied LIESST in an FeIIN4O2 spin-crossover material of lower symmetry, which allowed for quite intense and low-energy shifted d-d bands. By combining ab initio DFT and TD-DFT calculations and fs optical absorption measurements, we demonstrated that shorter intermediates enhanced coherent structural dynamics, and d-d excitation induced faster LS-to-HS switching, compared to MLCT.

Solvent tuned single molecule dual emission in protic solvents: effect of polarity and H-bonding.

Phen-PENMe2 has recently been proposed as a promising new molecule displaying solvent-tuned dual emission, highlighting an original and newly-described charge transfer model. The study of the photophysical behaviour of this molecule was extended to include protic solvents. The effects of polarity and hydrogen bonding lead to an even more evident dual emission associated with a large multi-emission band in some solvents like methanol, highlighting Phen-PENMe2 as a promising candidate for white light emission.

Red-light-driven photocatalytic hydrogen evolution using a ruthenium quaterpyridine complex.

A high-temperature, microwave synthesis of [Ru(qpy)3](2+) (qpy = 4,4':2',2'':4'',4'''-quaterpyridine) affords the photosensitiser in quantitative yield. The complex produces H2 photocatalytically in a range extending from the UV region of the spectrum to the red with greater efficiency when compared to [Ru(bpy)3](2+).

Solvent-tuned dual emission: a structural and electronic interplay highlighting a novel planar ICT (OPICT).

Displaying a dual emission, a Phen-PENMe2 compound can be foreseen as a new model for fundamental studies. It is based on an excited state cumulene-type structure, involving orthogonal π orbital (OPICT). In contrast to the "Twisted Intramolecular Charge Transfer" (TICT) emission, the OPICT emissive state is planar. This new compound is also a potential candidate for local ratiometric probes of medium polarity (mixture of solvents and biological systems) and white emission.

Pd-catalyzed homocoupling reaction of arylboronic acid: insights from density functional theory.

The key step in the mechanism of the Palladium-catalyzed homocoupling of arylboronic acids ArB(OH)(2)(Ar = 4-Z-C(6)H(4) with Z = MeO, H, CN) in the presence of dioxygen, leading to symmetrical biaryls, has been elucidated by using density functional theory. In particular, by starting from the peroxo complex O(2)PdL(2)(L = PPh(3)), generated in the reaction of dioxygen with the Pd(0) catalyst, the fundamental role played by an intermediate formed by coordination of one oxygen atom of the peroxo complex to the oxophilic boron atom of the arylboronic acid has been pointed out. This adduct reacts with a second molecule of arylboronic acid to generate a cis-Ar-Pd(OOB(OH)(2))L(2) complex that can form the stable intermediate trans-Ar-Pd(OH)L(2) (experimentally characterized) through a sequence of hydrolysis and isomerization reactions. All theoretical insights are in agreement and do substantiate the experimentally postulated mechanism. Furthermore, direct comparison of experimental and computed spectroscopic parameters (here, (31)P chemical shifts) allows us to confirm the formation of the intermediate.

Effect of self-interaction error in the evaluation of the bond length alternation in trans-polyacetylene using density-functional theory.

The calculation of the bond-length alternation (BLA) in trans-polyacetylene has been chosen as benchmark to emphasize the effect of the self-interaction error within density-functional theory (DFT). In particular, the BLA of increasingly long acetylene oligomers has been computed using the Møller-Plesset wave-function method truncated at the second order and several DFT models. While local-density approximation (LDA) or generalized gradient corrected (GGA) functionals strongly underestimate the BLA, approaches including self-interaction corrections (SIC) provide significant improvements. Indeed, the simple averaged-density SIC scheme (ADSIC), recently proposed by Legrand et al. [J. Phys. B 35, 1115 (2002)], provides better results for the structure of large oligomers than the more complex approach of Krieger et al. [Phys. Rev. A 45, 101 (1992)]. The ADSIC method is particularly promising since both the exchange-correlation energy and potential are improved with respect to standard LDA/GGA using a physically appealing correction, through a different route than the more popular approach through the Hartree-Fock exchange inclusion within the hybrid functionals.