Pt(II) Complexes with Tetradentate C^N*N^C Luminophores: From Supramolecular Interactions to Temperature-Sensing Materials with Memory and Optical Readouts

A series of four regioisomeric Pt(II) complexes (PtL(a)-n and PtL(b)-n) bearing tetradentate luminophores as dianionic ligands were synthesized. Hence, both classes of cyclometallating chelators were decorated with three n-hexyl (n = 6) or n-dodecyl (n = 12) chains. The new compounds were unambiguously characterized by means of multiple NMR spectroscopies and mass spectrometry. Steady-state and time-resolved photoluminescence spectroscopy as well quantum chemical calculations show that the effect of the regioisomerism on the emission colour and on the deactivation rate constants can be correlated with the participation of the Pt atom on the excited state. The thermal properties of the complexes were studied by DSC, POM and temperature-dependent steady-state photoluminescence spectroscopy. Three of the four complexes (PtL(a)-12, PtL(b)-6 and PtL(b)-12) present an intriguing thermochromism resulting from the responsive metal–metal interactions involving adjacent monomeric units. Each material has different transition temperatures and memory capabilities, which can be tuned at the intermolecular level. Hence, dipole–dipole interactions between the luminophores and disruption of the crystalline packing by the alkyl groups are responsible for the final properties of the resulting materials.