Influence of cyclodextrin size on fluorescence quenching in conjugated polyrotaxanes by methyl viologen in aqueous solution

• Published in: Journal of materials chemistry Vol. 19; no. 18; pp. 2846 - 2852
• Main Authors: ODDY, Francine E, BROVELLI, Sergio, STONE, Matthew T, KLOTZ, Eric J. F, CACIALLI, Franco, ANDERSON, Harry L
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2009
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electronics; Exact sciences and technology; Growth from solutions; Materials science; Methods of crystal growth; physics of crystal growth; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optoelectronic devices; Photoluminescence; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Encapsulation; Luminescence; Photoluminescence; Fluorescence; Light emitting diodes; Charge transport; Time resolved spectra; Luminescence decay; Macrocycle; Viologen polymer; Aggregation; Conjugated polymer; Cyclodextrin; Aqueous solutions; Wires; Size effect; Luminescence quenching; Crystal growth from solutions; Transport processes
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/b821950h

Poly(4,4'-diphenylenevinylene) rotaxanes and [2]rotaxanes with a-, b-, g-cyclodextrin macrocycles were synthesised and their sensitivities to fluorescence quenching by methyl viologen in aqueous solution were determined, relative to uninsulated analogues. Stern-Volmer analysis revealed that the fluorescence quenching response of polyrotaxanes is strongly dependent on the diameter of the cyclodextrins. Polyrotaxanes, composed of the smaller diameter a- or b-cyclodextrins, are the least easily quenched, with Stern-Volmer constants about two orders of magnitude smaller than from the wider g-cyclodextrin polyrotaxane and the uninsulated polymer. Time-resolved photoluminescence results demonstrate the crucial role of interchain aggregation on the sensitivity to fluorescence quenchers. The materials with the highest Stern-Volmer constants exhibit the most biexponential photoluminescence decay, which is indicative of aggregation, and the emission spectra of solutions containing methyl viologen resemble the early-time emission spectra (0-3 ns after excitation) of the unquenched samples. The results show that the threaded a-cyclodextrin is effective in preventing aggregation, and in hindering fluorescence quenching, even when only a small fraction of the conjugated polymer is encapsulated. This conclusion is relevant to the application of these materials in optoelectonic devices, such as light-emitting diodes, where it is essential to prevent luminescence quenching without hindering charge transport.