Ultrafast Energy Transfer from Fluorene Polymers to Single-Walled Carbon Nanotubes in Wrapped Carbon Nanotube Bundles

Conjugated polymers can selectively wrap around single walled carbon nanotubes (SWNTs) with specific chiral angles and diameters. Such a hybrid material containing both. SWNTs and polymers is attractive for applications such as organic photovoltaic devices and photosensors. In this study, we investigate excitation energy transfer (EET) in a paper form of semiconducting SWNTs wrapped by poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) by means of photoluminescence (PL) excitation spectroscopy and time-resolved luminescence spectroscopy. Photoluminescence excitation maps and spectra show PL peaks when the, 0-0 singlet transition of PFO is excited at 2.88 eV, as well as peaks corresponding to EET between semiconducting SWNTs wrapped by PFO. The PL decay time measured for a drop-cast PFO film is 82 ps, whereas the decay time due to PFO in the PFO-wrapped SWNT sample is as short as 0.38 ps. From these results, the EET rate between PFO and SWNTs is estimated to be 2.6 X 10(12) s(-1). Comparison of the highest occupied molecular orbitl and lowest unoccupied molecular orbital energy levels for PFO with the band edge energies of SWNTs indicates that EET can occur from the PFO to SWNTs with band gap energies in the range of 0.8 to 1.4 eV.