Modulation of Solid-State Aggregation and Chromic Behaviour of Chloride/Isocyanide Cyclometalated Platinum(II) Complexes

Résumé

Self-assembly of square-planar platinum(II) complexes to form supramolecular structures have been widely studied because of the strong tendency of their rigid skeleton to form intermolecular π···π and Pt···Pt interactions, which leads to assembly-induced luminescence of great relevance for applications in OLEDs, chemosensors and bioimaging.[1] Among the wide range of Pt(II) complexes, cyclometalated compounds containing the strong field isocyanide ligands are strongly emissive materials with photophysical characteristics which, on occasions, can be modulated by controlling their assembly, which constitutes a powerful tool for developing materials with stimuli-responsive luminescence properties. In this context and with the aim of investigating the influence of the isocyanide and cyclometalated ligands on the self-assembly and photophysical properties of Pt(II) compounds, we report here two series of Cl/CNR cyclometalated platinum complexes, [Pt(C^N)Cl(CNR)], with 2,6-dimethylphenyl (CNXyl) (1-3)[2] and tert-butyl (CNBut) (4-5) isocyanide ligands, featuring 2-phenylpyridine (ppy), 2,4-difluorophenylpyridine (dfppy), phenylquinoline (pq) and 4-(2-pyridyl)benzaldehyde (ppy-CHO) as cyclometalated ligands (C^N). We demonstrate in this work the fine modulation of molecular packing and emission properties by minor molecular structural variations or solvents using X-ray diffraction and theoretical studies. It was found that the planarity of phenylpyridine-based derivatives favours the formation of aggregates through π···π and/or Pt···Pt interactions in the ground and excited states, giving rise to different chromic behavior upon application of one or several stimuli. Complexes with CNXyl display interesting mechanochromic and Aggregation Induced Emission (AIE) luminescent effects, whereas with CNBut exhibit multi-stimuli responsive properties, such as vapochromism, solvatochromism, thermochromism and mechanochromism.