Photophysical studies of organostannoxane supported hexafluorophore assemblies

Abstract

The condensation reaction between n-butylstannoic acid and ArCOOH (Ar = 1-naphthyl-CH2 (1), 9-anthracenyl (2), 9-xanthenyl (3), 1-pyrenyl-(CH2)3 (4), 1-pyrenyl (5)) afforded hexameric organostannoxanes [n-BuSn(O)(O2CAr)]6 in high yield. The molecular structures of compounds 2 and 3 were confirmed by single crystal X-ray diffraction analysis. These compounds possess a drum-like structure and each molecule is attached with six fluorophores through carboxylate functionality. 119Sn NMR and MALDI-TOF analyses suggest that the compounds 1, 4, and 5 also belong to the family of organotin drum structure. There are also various intra- and intermolecular interaction between the fluorophores. In particular, compound 2 shows a strong intramolecular hydrogen bond (CH····π 2.489 Å) between two anthracene moieties. However, such interaction is weaker in 3. The absorption spectra of 1–5 indicate that λmax was very slightly red-shifted with respect to their fluorophore carboxylic acid. Fluorescence measurements reveal that these molecules are good blue emitters in solution state but red-shifted in the solid-state. Quantum yield calculation shows that emission efficiencies decreased for smaller spacers between fluorophore and stannoxane core. We have carried out thermal studies for all compounds. These suggest that the compounds are robust and stable until about 300 °C. Interestingly, we have demonstrated the synthesis of SnO2 from the hexameric organotin drum 3 by heating in the temperature range 600–1200 °C.