Luminescent Alkynylplatinum(II) Terpyridyl Metallogels Stabilized by Pt•••Pt, π-π, and Hydrophobic-Hydrophobic Interactions

A series of luminescent alkynylplatinum(II) terpyridyl complexes have been synthesized and characterized by H-1 NMR, IR, FAB-mass spectrometry, and elemental analysis; one of the platinum(II) complexes has also been structurally characterized by X-ray crystallography. Their electrochemical and photophysical properties have also been investigated. A majority of the complexes were able to form stable thermoreversible metallogels inorganic solvents, tested by the stable-to-inversion of a test tube method. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of the xerogels showed typical fibrous structures on the micrometer scale. Interestingly, whereas 2-OTf, 3-OTf, and 5-PF6 formed thermotropic metallogels mainly through van der Waals' forces with different emission colors, 1-X (X = OTf, BF4, PF6, and ClO4) showed additional Pt center dot center dot center dot Pt and pi-pi interactions to stabilize the resultant metallogels and showed drastic color changes during the gel-to-sol phase transition. The metallogels of I-X were also different colors, depending on the nature of the counter anions, which governs the degree of aggregation and the extent of Pt center dot center dot center dot Pt and pi-pi interactions involved in the gelation process. This property may be utilized to serve as an effective reporter for microenvironmental changes.