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 P2(1)/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 P2(1)2(1)2(1). 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).