Unusual Luminescence Enhancement of Metallogels of Alkynylplatinum(II) 2,6-Bis(N-alkylbenzimidazol-2′-yl)pyridine Complexes upon a Gel-to-Sol Phase Transition at Elevated Temperatures

• Published in: Journal of the American Chemical Society Vol. 131; no. 17; pp. 6253 - 6260
• Main Authors: Tam, Anthony Yiu-Yan, Wong, Keith Man-Chung, Yam, Vivian Wing-Wah
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06-05-2009
• Subjects: Gels - chemistry; Luminescence; Organoplatinum Compounds - chemical synthesis; Organoplatinum Compounds - chemistry; Phase Transition; Pyridines - chemistry; Temperature
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja900895x

A series of alkynylplatinum(II) complexes of 2,6-bis(N-alkylbenzimidazol-2′-yl)pyridine has been synthesized and characterized by 1H NMR, IR, FAB mass spectrometry, and elemental analysis; the photophysical properties have also been investigated. All the complexes have been shown to exhibit interesting gelation properties. Scanning electron microscopy (SEM) of the xerogels showed a network of fibrous structures, typical of morphologies of organogels/metallogels. Interestingly, two of the complexes were found to show strong luminescence enhancement upon a gel-to-sol phase transition upon increasing the temperature. This unusual behavior is rarely encountered, as it represents a sharp contrast to that exhibited by other typical thermotropic organogels and metallogels reported so far. Variable-temperature UV−vis and luminescence spectroscopies were performed to probe the gel-to-sol phase transition. Concentration-dependent, variable-temperature, and time-resolved emission studies in dilute benzene solution have also been made to provide further insights into the spectroscopic origin in the sol forms. A quantitative treatment of the system based on the Birks scheme has been performed.