Functionalized carbon nanotubes with tethered pyrenes: Synthesis and photophysical properties

Single-walled (SWNTs) and multiple-walled carbon nanotubes (MWNTs) were functionalized with dendra of tethered pyrene species, where the tether length was varied. These functionalized carbon nanotube samples are soluble in common organic solvents, making it possible to characterize the samples and to investigate and compare the photophysical properties of the tethered pyrene moieties in homogeneous solution. In general, the pyrene monomer excited state is significantly quenched by two competing processes of "intramolecular" excimer formation and energy transfer to the nanotube. The excimer formation is dynamic in nature, and the excimer emission is also quenched by the energy transfer, contributing to the overall low fluorescence quantum yields and rapid fluorescence decays. There are effects of the tether length on photoexcited-state properties of the pyrene species according to a comparison of the results obtained in solution vs in solid-state polymer matrix. The structurally more flexible environment for the pyrene moiety associated with a longer tether is more favorable to the excimer formation and less favorable to the excited-state energy transfer. The mechanistic implication of the results and potential applications of such materials are discussed.