Experimental and theoretical studies on photophysical properties: tuning redox-active amido-tetrathiafulvalene derivatives in paramagnetic coordination complexes.

Amido-5-pyrimidine (1), -4-pyridine (2), -2-pyrazine (3), -2-pyridine (4), and -2-pyridine-N-oxide (5) derivatives of TTF (TTF = tetrathiafulvalene) have been synthesized and characterized. The crystal structure of 1 has been resolved. Their capacities to coordinate paramagnetic transition metal have been explored. The following new molecular compounds have been synthesized and obtained as single crystals: {Cu(hfac)(2)(1)}(2) (6), cis-Mn(hfac)(2)(2)(2)(2) (7), trans-[Cu(hfac)(2)(3)(2)] (8), trans-[Cu(hfac)(2)(4)(2)] (9), and trans-[M(hfac)(2)(5)(2)] (M = Cu (10), Mn (11), Zn (12)). The crystal structures reveal that the nature of the coordinating substituent plays a fundamental role on the crystalline organization. Cyclic voltammetry measurements have been performed for all the species and they have permitted us to observe the redox activity of the free and linked donors. EPR measurements are in agreement with the solid-state structures. All the ligands and corresponding coordination complexes have been studied by UV-visible absorption spectroscopy. Gaussian deconvolutions have been performed to fit the experimental solid-state absorption curves. Molecular orbital diagram for ligands 4 and 5; and their coordination complexes have been determined. The nature of the thirty to fifty low-lying monoelectronic transitions occurring in the TTF derivatives have been identified by TD-DFT calculations and their corresponding UV-visible absorption spectra have been simulated. Concerning the open-shell complexes, the excitations in the low energy region of their spectra have been calculated to determine the coordination effect on the TTF to acceptor transitions of the ligand fragments.