2-Azabutadiene complexes of rhenium(i): S,N-chelated species with photophysical properties heavily governed by the ligand hidden traits

The reaction of [Re(CO)(3)(THF)(mu-Br)](2) or [Re(CO)(5)X] (X = Cl, Br, I) with the diaryl-2-azabutadienes [(RS)(2)C = C(H)-N = CAr2] containing two thioether arms at the 4,4-position forms the luminescent S,N-chelate complexes fac-[(OC)(3)ReX{(RS)(2)C = C(H)-N = CAr2}] (1a-h). The halide abstraction by silver triflate converts [(OC)(3)ReCl{(PhS)(2)C = C(H)-N = CPh2}] (1c) to [(OC)(3)Re(OS(= O)(2)CF3){(PhS)(2)C = C(H)-N = CPh2}] (1j) bearing a covalently bound triflate ligand. The cyclic voltammograms reveal reversible S<\^>N ligand-centred reduction and irreversible oxidation waves for all complexes. The crystal structures of nine octahedral complexes have been determined along with that of (NaphtylS)(2)C = C(H)-N = CPh2 (L6). A rich system of weak non-covalent intermolecular secondary interactions through CHMIDLINE HORIZONTAL ELLIPSISX(Cl, Br)Re, CHMIDLINE HORIZONTAL ELLIPSISO, COMIDLINE HORIZONTAL ELLIPSIS pi(Ph), CHMIDLINE HORIZONTAL ELLIPSIS pi CO, CHMIDLINE HORIZONTAL ELLIPSISO and CHMIDLINE HORIZONTAL ELLIPSISS contacts has been evidenced. The photophysical properties have been investigated by steady-state and time-resolved absorption (fs transient absorption, fs-TAS) and emission (ns-TCSPC and ps-Streak camera) spectroscopy in 2-MeTHF solution at 298 and 77 K. The emission bands are composed of either singlet (450 < lambda(max) < 535 nm) and/or triplet emissions (at 77 K only, lambda(max) < 640 nm, or appearing as a tail at lambda > 600 nm), which decay in a multiexponential manner for the fluorescence (short ps (i.e.