Organo- and hydrogelators based on luminescent monocationic terpyridyl platinum(II) complexes with biphenylacetylide ligands

A series of phosphorescent terpyridyl platinum(II) complexes with ancillary biphenylacetylide ligands, namely, [(R(3)tpy)PtC≡C(biphenyl)]X (R=tBu, H, or Et(2)N; tpy=2,2';6',2''-terpyridyl; X is an anion) were synthesized and structurally characterized by various spectroscopic techniques and X-ray diffraction methods. Despite a lack of long alkyl chain(s) or hydrogen-bonding motif(s), complexes [(tpy)PtC≡C(biphenyl)]Cl and [(tBu(3)tpy)PtC≡C(biphenyl)]X (X=Cl, ClO(4), PF(6), or BF(4)) were found to gelate water and organic solvents, respectively. The self-aggregation of these complexes in solutions and the resulting gels were investigated with variable-temperature (VT) (1)H NMR spectroscopy, polarized optical microscopy, and absorption/emission spectroscopy. SEM micrographs on dry gels revealed entangled nanofibers with diameters of 20-40 nm and lengths of tens of micrometers. Powder X-ray diffraction (PXRD) study revealed various degrees of crystallinity of these fibrillar nanostructures. The substituents on both the terpyridyl and acetylide ligands and counterion of these complexes play a profound but concerted role in tuning the intermolecular metal···metal and/or π-π interactions, and hence the gelation properties.