Solid–Solid Phase Transitions in [trans-Pt(PMe3)2(C≡CC6H4R)2]-Containing Materials (R = O(CH2)nH; n = 6, 9, 12, and 15)

The title complexes were prepared in Hagihara conditions and were investigated by single crystal X-ray crystallography (n = 6, [Pt]C6; n = 12, [Pt]C12), X-ray powder diffraction (powder XRD), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA, [Pt]C12), and steady-state and time-resolved solid state UV–vis and emission spectroscopy at 298 and 77 K. [Pt]C6 complex exhibits no phase change with the temperature. Concurrently, [Pt]C9 (n = 9) and [Pt]C12 complexes exhibit an irreversible Tendo values of 104 and 119 °C, respectively, associated with a thermal annealing. Finally, [Pt]C15 (n = 15) complex exhibit a reversible thermal processes with a large hysteresis (Tendo = 126 °C, Texo = 140 °C) followed by a glass transition (Tendo = 146 °C, Texo = 69 °C) as depicted by DSC. These phase changes are accompanied by a decrease in triplet excited state lifetimes upon cycling the sample temperature over and under the transition temperatures. These various thermal processes induce a significant decrease in emission lifetimes, strongly suggesting the presence of a reorganization of the complexes in the solid state favoring more chain-chromophore contacts, thus promoting nonradiative "knocking" processes.