Acetylenic Substituent: Influence on the Structure, Electrochemical, Photophysical, and Thermal Properties of Rhenium(I) and Platinum(II) Complexes

The 'wire-like' acetylenic moiety is an important building block in organic and coordination chemistry that can facilitate electron transfer in donor-acceptor compounds, contributing to the enhancement of their photophysical properties. 2,6-Bis-(thiazol-2-yl)pyridine (<i>dtpy</i>) functionalized with a 4-phenylacetylene group (Ph-C≡C-<i>dtpy</i>) was, for the first time, used for the preparation of [ReCl(CO)₃(Ph-C≡C-<i>dtpy</i>)] and [Pt(Ph-C≡C-<i>dtpy</i>)Cl]CF₃SO₃ in order to understand the properties derived from the use of the acetylenic substituent. The coordination ability of Ph-C≡C-<i>dtpy</i> toward Pt(II) and Re(I) centers was determined. All the studied compounds were characterized using FT-IR, ¹H NMR, and ¹³C NMR spectroscopies, elemental analysis and, in the case of the free ligand and rhenium(I) complex, single-crystal X-ray analysis was also used. Their electrochemical, photophysical, and thermal properties were compared with the previously described similar systems. The photoluminescence spectra of Ph-C≡C-<i>dtpy</i>, [ReCl(CO)₃(Ph-C≡C-<i>dtpy</i>)] and [Pt(Ph-C≡C-<i>dtpy</i>)Cl]CF₃SO₃ were investigated in solution and in the solid state at 298 K and 77 K. The experimental results were supported by the DFT and TD-DFT calculations. As a result of the introduction of the -C≡C- moiety into the organic ligand skeleton, the Re(I) and Pt(II) complexes display room-temperature emission. In the case of [Pt(Ph-C≡C-<i>dtpy</i>)Cl]CF₃SO₃, photoluminescence lifetime in a microsecond regime was observed, whereas nanosecond lifetime for [ReCl(CO)₃(Ph-C≡C-<i>dtpy</i>)] in solution is comparable to lifetimes previously observed for rhenium(I) compounds with 4-substituted <i>dtpys</i>.