Photoisomerisation in Aminoazobenzene-Substituted Ruthenium(II) Tris(bipyridine) Complexes: Influence of the Conjugation Pathway.

Transition-metal complexes containing stimuli-responsive systems are attractive for applications in optical devices, photonic memory, photosensing, as well as luminescence imaging. Amongst them, photochromic metal complexes offer the possibility of combining the specific properties of the metal centre and the optical response of the photochromic group. The synthesis, the electrochemical properties and the photophysical characterisation of a series of donor-acceptor azobenzene derivatives that possess bipyridine groups connected to a 4-dialkylaminoazobenzene moiety through various linkers are presented. DFT and TD-DFT calculations were performed to complement the experimental findings and contribute to their interpretation. The position and nature of the linker (ethynyl, triazolyl, none) were engineered and shown to induce different electronic coupling between donor and acceptor in ligands and complexes. This in turn led to strong modulations in terms of photoisomerisation of the ligands and complexes.

Electronic structure of modelized vs. real carbon-chain containing organometallic dinuclear complexes: similarities and differences.

DFT calculations were carried out on the homo- and hetero-bimetallic model wires [(η(5)-C5H5)(dpe)Fe-C≡C-C6H4-C≡C-Fe(dpe)(η(5)-C5H5)] (1'), [(η(7)-C7H7)(dpe)Mo-C≡C-C6H4-C≡C-Mo(dpe)(η(7)-C7H7)] (2'), and [(η(5)-C5H5)(dpe)Fe-C≡C-C6H4-C≡C-Mo(dpe)(η(7)-C7H7)] (3') used to tentatively mimic [(η(5)-C5Me5)(dppe)Fe-C≡C-C6H4-C≡C-Fe(dppe)(η(5)-C5Me5)] (1), [(η(7)-C7H7)(dppe)Mo-C≡C-C6H4-C≡C-Mo(dppe)(η(7)-C7H7)] (2), and [(η(5)-C5Me5)(dppe)Fe-C≡C-C6H4-C≡C-Mo(dppe)(η(7)-C7H7)] (3), respectively in order to analyze the similarities and the differences between models and real compounds previously theoretically and experimentally studied, with respect to their molecular structures and properties. A comparison of the metrical data computed for the models and the real systems shows some slight discrepancy between the metal-ancillary ligand distances - shorter distances are observed in the formers - but comparable metal-Cα and Cα-Cß distances. Incidentally, distances computed for the model molecules match more closely those measured experimentally. Replacement of a dppe ligand tethered to the metal centers by a dpe group does not much alter the electronic properties. Therefore, overall, data obtained for the Mo2 models 2' compare rather well with those computed for the real systems 2. Larger alteration is noticed when Cp* is substituted by Cp, even if the general trends observed for the real iron species 1 and 3 are kept overall for the iron models 1' and 3'. Indeed, the smaller electron-donor properties of Cp affect somewhat the nodal properties of the HOMOs (less metallic character) and increase the HOMO-LUMO gaps and the ionization potentials. Despite this, similarities between models and real compounds largely overtake differences. It is shown that calculations on models provide quite acceptable results.

Aggregation effect on the luminescence properties of phenylbipyridine Pt(II) acetylide complexes. A theoretical prediction with experimental evidence.

We report a combined theoretical and experimental study of both the structural and optical properties of phosphorescent cyclometalated square-planar (phenylbipyridyl)platinum(II) acetylide complexes, namely (Pt(tBu2-CN̂N)(C≡C-Ph)] and (Pt(hex2-CN̂N)(C≡C-thienyl)] that exhibit, at high concentrations, an additional emission band at longer wavelength. The geometry optimizations of both the ground and the lowest triplet excited states of the considered monomers and different possible dimers have been performed in solution using several density functional theory (DFT) functionals corrected for dispersion effects. For the dimers, which are shown to exhibit a head-to-tail configuration, a significant shortening of the Pt···Pt distance, compared to that in the ground state, is observed in the first triplet state. Moreover, we show that trimeric species are highly improbable in solution. The UV-visible absorption spectra of the complexes are well rationalized using a vertical time-dependent DFT (TD-DFT) protocol relying on a global hybrid exchange-correlation functional. Finally, the new emission band at high concentration of the complexes can be assigned to a metal-metal to ligand charge transfer excited state ((3)MMLCT).

Triaryl-1,3,5-triazinane-2,4,6-triones (isocyanurates) peripherally functionalized by donor groups: synthesis and study of their linear and nonlinear optical properties.

The linear optical (LO) and nonlinear optical (NLO) properties of a series of isocyanurates functionalized by donor arms at the periphery are reported herein. These octupolar derivatives were obtained in a straightforward way from commercial isocyanate derivatives and were fully characterized. Although several of these compounds are known, those that exhibited the largest NLO activities are all new compounds. In terms of second-order activity, several of these derivatives exhibit remarkable activity/transparency tradeoffs. In terms of third-order activity, the longer derivatives with the stronger donor groups (X = NH(2), NMe(2), or NPh(2)) were shown to possess significant two-photon absorption cross sections. These strongly luminescent derivatives exhibit two-photon absorption cross sections up to 410 GM. DFT computations were also conducted to unravel their electronic structures and to rationalize their NLO properties. To our knowledge, the present study is the first concerned with the nonlinear optical properties of these original cyclotrimers.