ABSTRACT
The new cyrhetrenyl acylhydrazone [(CO)3 Re(η5 -C5 H4 )-C(O)-NH-N = C(CH3 )-(2-C4 H2 S-5-NO2 )] (E-CyAH) has been designed, synthesized and fully characterized to study the effect of having a cyrhetrenyl fragment (sensitizer) covalently bonded to an acylhydrazone moiety (switch), on its photophysical and photochemical properties. The crystal structure reveals that E-CyAH adopts an E-configuration around the iminic moiety [-N = C(CH3 )]. The absorption spectrum of E-CyAH displays two bands at 270 and 380 nm, which are mainly ascribed to π â π* intraligand (IL) and dπ â π* metal-to-ligand charge transfer (MLCT) transitions, being consistent with DFT/TD-DFT calculations. Upon 365 nm irradiation, E-CyAH photoisomerizes to Z-CyAH, as evidenced by UV-Vis and 1 H-NMR spectral changes, with a quantum yield value ΦE -CyAH â Z -CyAH of 0.30. Z-CyAH undergoes a first-order thermal back-isomerization process, with a relatively short half-life τ1/2 of 277 min. Consequently, E-CyAH was quantitatively recovered after 24 h, making it a fully reversible T-type molecular photoswitch. This remarkable behavior allows us to measure the individual photophysical properties for both isomers. In addition, E-CyAH and Z-CyAH efficiently photosensitize the generation of singlet oxygen (O2 (1 Δg )) with good yield (ΦΔ = 0.342).
ABSTRACT
A set of new copper(i) complexes is synthesized and characterized using a labile PNP pincer ligand (PNP = N,N'-bis(diphenylphosphine)-2,6-diaminopyridine). A homoleptic Cu(i) complex [Cu(PNP-κP1:κN1)2]+, (1), was prepared, and taking advantage of the uncoordinated phosphorus atoms in (1), reaction with a second Cu(i) atom bearing secondary ligands (PPh3, phen or dmp) allows the formation of new complexes: a bimetallic helicate [Cu(PNP)2(phen)]2+, (2), a mononuclear pincer complex [CuI(PNP)(PPh3)]+, (3), and a heteroleptic complex [CuI(PNP)(dmp)]+, (4). All complexes were characterized by X-ray crystallography, NMR (VT-NMR for (1) and (4)), cyclic-voltammetry, and steady-state and time-resolved luminescence spectroscopy. The fluxional behavior in (1) was studied by 31P VT-NMR, where an Ea value of 47.42 kJ mol-1 was calculated for the intramolecular alternating coordination of -PPh2 moieties in PNP to the metal atom. This set of compounds reveals the versatility of the PNP ligand when added to the coordinating properties of Cu(i). The four complexes exhibit emission in solution and complexes (2)-(4) display intense luminescence in the solid state. The oscillographic traces showing the decay of the luminescence were fitted to biexponential functions with time constants: 8.0 µs > τem,1 > 0.37 µs and 50 µs >τem, 2 > 2.2 µs for complexes (2), (3) and (4), respectively. Radiative relaxation is associated with electronic transitions in both the ligand PNP and metal-to-ligand charge transfer (MLCT).
ABSTRACT
Complexation of copper(I) with the binucleating ligand, 1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane, mphenpr, result in formation of helical dimers, [Cu2(mphenpr)2](2+). The resolution of the enantiomeric forms of the dimers has been carried out with Δ-[As(cat)3](-) as resolving agent and X-ray structures for two compounds, P-[Cu2(mphenpr)2](Δ-[As(cat)3])2 and P-[Cu2(mphenpr)2](Δ-[As(cat)3])2·4(CH3CN), are reported. The rate of racemization in poorly-coordinating solvents has been examined by (1)H NMR, and is slow. At saturating concentrations of [[Cu2(mphenpr)2](2+)] in acetonitrile, crystals of the helical trimeric complex [Cu3(mphenpr)3](ClO4)3 are obtained. The X-ray structure of the trimer is reported. This species has also been resolved. As with the helical dimer, racemization in poorly-coordinating solvents is slow, and circular dichroism and (1)H NMR spectra are reported. The absolute configuration of the resolved complex, P-[Cu3(mphenpr)3](Δ-[As(cat)3])3, has been determined by X-ray crystallography.