The preparation, spectroscopic characterization, and X-ray crystal structure of two novel one-dimensional compounds of formula [MII(tppz)­(NCS)­(μ-1,3-NCS)] n [tppz = 2,3,5,6-tetrakis­(2-pyridyl)­pyrazine and M = Co­(1) and Ni (2)] are reported. 1 and 2 are isomorphous compounds, and they crystallize in the P21/n space group. Their structures are made up of zigzag chains of cobalt­(II) (1) and nickel­(II) ions (2) bridged by single end-to-end thiocyanate groups with a tridentate tppz molecule and a terminally bound thiocyanate-N ligand achieving distorted MN5S octahedral surroundings around each metal center. The main source of the distortion of the ideal octahedron is due to the geometrical constraints issued from the occurrence of two fused five-member chelate rings of the tridentate tppz ligand, the values of the N–M–N bond angles covering the range 75.58(9)–78.66(9)°. The M–N bond lengths vary in the range 2.025(3)–2.116­(29 (1) and 2.001(2)–2.079(2) Å (2), and they are shorter than the M–S bond distance [2.6395(10) (1) and 2.5225(9) Å (2)]. The values of the intrachain metal–metal separation are 6.4197(7) (1) and 6.3257(5) Å (2). The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9–300 K. Both compounds exhibit intrachain ferromagnetic interactions with values of the magnetic coupling (J) of +4.60 (1) and +7.82 cm–1 (2) [the spin Hamiltonian being defined as Ĥ = −JΣ i = 1 n–1 Ŝ i Ŝ i+1].

In the current work, comprehensive photophysical and electrochemical studies were performed for eight rhenium(I) complexes incorporating 2,2′:6′,2″-terpyridine (terpy) and 2,6-bis(pyrazin-2-yl)pyridine (dppy) with appended 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl, and 1-pyrenyl groups. Naphthyl and phenanthrenyl substituents marginally affected the energy of the MLCT absorption and emission bands, signaling a weak electronic coupling of the appended aryl group with the Re(I) center. The triplet MLCT state in these complexes is so low lying relative to the triplet 3 IL aryl that the thermal population of the triplet excited state delocalized on the organic chromophore is ineffective. The attachment of the electron-rich pyrenyl group resulted in a noticeable red shift and a significant increase in molar absorption coefficients of the lowest energy absorption of the resulting Re(I) complexes due to the contribution of intraligand charge-transfer (ILCT) transitions occurring from the pyrenyl substituent to the terpy/dppy core. At 77 K, the excited states of [ReCl(CO) 3 (L n -κ 2 N )] with 1-pyrenyl-functionalized ligands were found to have predominant 3 IL pyrene / 3 ILCT pyrene→terpy character. The 3 IL/ 3 ILCT nature of the lowest energy excited state of [ReCl(CO) 3 (4′-(1-pyrenyl)-terpy-κ 2 N )] was also evidenced by nanosecond transient absorption and time-resolved emission spectroscopy. Enhanced room-temperature emission lifetimes of the complexes [ReCl(CO) 3 (L n -κ 2 N )] with 1-pyrenyl-substituted ligands are indicative of the thermal activation between 3 MLCT and 3 IL/ 3 ILCT excited states. Deactivation pathways occurring upon light excitation in [ReCl(CO) 3 (4′-(1-naphthyl)-terpy-κ 2 N )] and [ReCl(CO) 3 (4′-(1-pyrenyl)-terpy-κ 2 N )] were determined by femtosecond transient absorption studies.

The impact of highly electron donating units appended to the imine ligand on the thermal and optoelectronic properties of Re(i) complexes was investigated.

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