Fast and slow time regimes of fluorescence quenching in conjugated polyfluorene-fluorenone random copolymers: The role of exciton hopping and dexter transfer along the polymer backbone

Dias, FB; Knaapila, M; Monkman, AP; Burrows, HD

Abstract

The luminescence decay kinetics of polyfluorene copolymers containing fluorenone units randomly distributed along the polymer chain have been Studied by steady-state and time-resolved fluorescence techniques in toluene solution. The typical green emission from polyfluorenes containing 9-fluorenone moieties is only observed if the 9-fluorenone group is covalently attached to the polymer. Small-angle neutron scattering (SANS) measurements indicate that, independent of the 9-fluorenone fraction, all the studied copolymers adopt an open wormlike conformation. This prevalent 1-dimensional arrangement confirms that the green emission observed with polyfluorenes is not the result of excimer formation in the typical sandwich-like conformation. Analysis of time-resolved fluorescence decays by the maximum entropy method (MEM) collected at the polyfluorene emission (415 nm) and by global analysis of decays collected at 415 and 580 nm (the 9-fluorenone defect emission wavelength) clearly indicates two different time regimes in the Population of the fluorenone defect: one occurring in the time interval of 10 to 30 ps and a second one occurring in the time range from 70 to 200 ps. While the slower process shows a linear dependence with the 9-fluorenone fraction, compatible with a hopping migration process along the polymer chain, the faster process does not show such a dependence and instead suggests a short-range Dexter mechanism. These findings are in agreement with our previous work where the presence of a faster component was suggested.

Citation

Dias, F., Knaapila, M., Monkman, A., & Burrows, H. (2006). Fast and slow time regimes of fluorescence quenching in conjugated polyfluorene-fluorenone random copolymers: The role of exciton hopping and dexter transfer along the polymer backbone. Macromolecules, 39(4), 1598-1606

• Journal Article Type: Article
• Publication Date: 2006-02
• Journal: Macromolecules
• Print ISSN: 0024-9297
• Electronic ISSN: 1520-5835
• Publisher: American Chemical Society
• Volume: 39
• Issue: 4
• Pages: 1598-1606
• Keywords: PHOTON-HARVESTING POLYMERS; MAXIMUM-ENTROPY METHOD; ENERGY-TRANSFER; LIFETIME DISTRIBUTIONS; GREEN EMISSION; LUMINESCENCE; DYNAMICS; MIGRATION; CHAIN; POLYTHIOPHENE
• Public URL: https://durham-repository.worktribe.com/output/1536329