Dynamics of Forster transfer in polyfluorene-based polymer blends and Langmuir-Blodgett nanostructures

We have studied the Forster transfer dynamics in spin-cast polyfluorene blends and Langmuir-Blodgett (LB) nanostructures by time-resolved photoluminescence (PL) spectroscopy. The blend system consisted of poly(9,9-dioctylfluorene) (F8) as the host and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) as the guest. In the spin-cast films we find evidence for phase separation at high F8BT concentrations. In the LB nanostructures, the host-guest separation is precisely controlled by optically-inert monolayer spacers of stearic acid. This permits a quantitative analysis of the Forster transfer dynamics, from which we deduce a value of 38 +/- 7 Angstrom for the Forster radius of the F8-F8BT system, in agreement with the predictions based on spectral overlap calculations. (C) 2003 Elsevier Science B.V. All rights reserved.