Organo‐ and Hydrogelators Based on Luminescent Monocationic Terpyridyl Platinum(II) Complexes with Biphenylacetylide Ligands

Abstract

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.

Multiaddressable molecular rectangles with reversible host–guest interactions: Modulation of pH-controlled guest release and capture

“…The electronic absorption spectra of alkynylplatinum(II) terpyridine molecular rectangles 1−4 in dichloromethane solution at room temperature displayed intense intraligand [π → π*] transitions of the terpyridine and the alkynyl ligands at 250−345 nm together with the moderately intense absorptions at 420−490 nm, which are assigned as admixtures of metal-to-ligand charge transfer (MLCT) [dπ(Pt) → π*(terpyridine)] and ligand-to-ligand charge transfer (LLCT) [π(C≡CR) → π*(terpyridine)] transitions according to previous spectroscopic studies on alkynylplatinum(II) terpyridine systems (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). Molecular rectangles 1−4 in degassed acetonitrile solution and solid state at 298 K exhibited structure-less emission bands at 620−700 nm, which are tentatively assigned as originated from the 3 MLCT/ 3 LLCT [dπ(Pt)/ π(C≡CR) → π*(terpyridine)] excited state with similar trends to their electronic absorptions.…”

“…2). It is believed that the newly formed low-energy absorptions and emissions are derived from a metal-metal-to-ligand chargetransfer (MMLCT) transition and 3 MMLCT excited state, respectively, as a result of the Pt(II)···Pt(II) and π−π interactions associated with the host-guest interaction on guest capture (23)(24)(25)(26)(27)(28). However, the flexible molecular rectangle 4 only resulted in The Job's method of continuous variation, electrospray ionization mass spectrometry (ESI-MS), and 2D NMR studies have been performed to provide a more thorough understanding of the binding mode in the host-guest assembly.…”

“…It was not until 2001 that the first successful synthesis of platinum(II) terpyridine alkynyl complexes, which possess enhanced solubility and luminescence compared with the chloro counterpart, was reported (16). Additional efforts have been devoted to the use of the system to respond to external stimuli, such as variation in solvent composition (17,18), pH (19,20), temperature (21,22), addition of ionic (24)(25)(26), and polymeric species (27,28), in which spectral changes induced by strong Pt(II)···Pt(II) and π−π interactions have been displayed.…”

A Platinum(II) Terpyridine Metallogel with an L‐Valine‐Modified Alkynyl Ligand: Interplay of Pt⋅⋅⋅Pt, π–π and Hydrogen‐Bonding Interactions

“…Since 2007, our group and others have reported several examples of the gelation of platinum(II) polypyridine alkynyl systems 15. 16 It was found that only with nonbulky substituents on the polypyridine rings could drastic absorption and/or emission changes be observed upon sol–gel transition 17b,c. More interestingly, it was also found that the Pt ⋅⋅⋅ Pt interactions do not necessarily become enhanced during sol–gel transition, but are dependent on the molecular packing.…”

Selbstorganisation und Bildung von (Hydro‐)Gelen durch kooperative π‐π‐Wechselwirkungen und unkonventionelle C‐H⋅⋅⋅X‐Wasserstoffbrücken

“…[8] Mit diesen Vorkenntnissen entwarfen wir einen amphiphilen Pt II -Komplex 2, in dem zwei hydrophobe Oligo(phenylenethinylen)(OPE)-Gerüste [9] mit je drei hydrophilen Triethylenglykol(TEG)-Ketten über terminale Pyridinringe an ein zentrales Pt II -Ion koordinieren (Schema 1). [10] Unser System erfüllt die oben erwähnten Voraussetzungen, da es neben einer recht ausgedehnten aromatischen Oberfläche eine Cl-Pt II -Cl-Einheit enthält, sowie eine große Anzahl durch elektronegative Sauerstoffheteroatome polarisierte Methylengruppen, die in der Lage sind, einen Beitrag zu schwachen Wasserstoffbrü-cken zu leisten. Demnach wurde angenommen, dass sich die Moleküle von 2 durch eine Kombination von kooperativen C-H···X-und p-p-Wechselwirkungen zusammenlagern, da das Vorhandensein von sterisch anspruchsvollen Chloratomen und von bis zu sechs sperrigen TEG-Ketten eine parallele Anordnung der Monomere [11] und somit das Auftreten von metallophilen Pt···Pt-Wechselwirkungen behindert.…”