A new polymorph of terpyridine: variable temperature X-ray diffraction studies and solid state photophysical properties

Abstract

The crystal structure of a new monoclinic polymorph of 2,2′ : 6′,2″ terpyridine (terpy) that contains two independent but structurally similar molecules, and crystallises in a space group P2₁/c, is reported. Variable-temperature single-crystal X-ray diffraction studies at 100, 150, 200 and 250 K show that the b-axis length increases significantly with increasing temperature. The molecules pack in a sandwich herringbone arrangement and the intermolecular non-bonded contacts are described in detail. All structural results are contrasted with those obtained for the previously reported polymorph of terpyridine, which crystallises in the orthorhombic space group P2₁2₁2₁. Photophysical properties of the new polymorph of terpyridine are also reported. The solid-state room temperature UV/vis absorption and emission spectra were measured. The sample was found to phosphoresce on the millisecond timescale, this being measured as a function of temperature (100–280 K). Its long-lived phosphorescent nature also allowed a pseudo-steady-state to be built up by continuous laser pumping (at 10 Hz repetition rate), which was investigated as a function of temperature (100–280 K).