Luminescent alkynylplatinum(II) terpyridyl metallogels stabilized by Pt ⋯Pt, π-π and hydrophobic-hydrophobic interactions

Abstract

A series of luminescent alkynylplatinum(II) terpyridyl complexes have been synthesized and characterized by 1H 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 in organic 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- • -Pt and π-π interactions to stabilize the resultant metallogels and showed drastic color changes during the gel-to-sol phase transition. The metallogels of 1-X were also different colors, depending on the nature of the counter anions, which governs the degree of aggregation and the extent of Pt ⋯ Pt and π-π interactions involved in the gelation process. This property may be utilized to serve as an effective reporter for microenvironmental changes. © 2009 American Chemical Society.