Staff profile
Publication details for Professor Andy Monkman
Dias, FB, Maiti, M, Hintschich, SI & Monkman, AP (2005). Intramolecular fluorescence quenching in luminescent copolymers containing fluorenone and fluorene units: A direct measurement of intrachain exciton hopping rate. Journal Of Chemical Physics 122(5): 11.- Publication type: Journal papers: academic
- ISSN/ISBN: 0021-9606
- Keywords: TIME-RESOLVED FLUORESCENCE; CONJUGATED POLYMERS; ENERGY-TRANSFER; GREEN EMISSION; STEADY-STATE; POLYFLUORENE; PICOSECOND; DYNAMICS; DEFECTS; KINETICS
Author(s) from Durham
Abstract
The quenching process of fluorescence emission in polyfluorene (PF) due
to the presence of intramolecular 9-fluorenone (9FL) moieties is
studied in dilute toluene solution as a function of 9FL content in
eight copolymers containing both fluorene and fluorenone units
(PF/FLx). The absorption spectrum of PF/FLx copolymers clearly shows a
new absorption band, redshifted relatively to the PF and 9-fluorenone
absorption, which increases in intensity when the fluorenone fraction
increases and also decreases with solvent polarity. Fluorescence
emission spectra of PF/FLx show that this redshifted and unstructured
emission does not coincide with the 9-fluorenone emission and, with
increasing solvent polarity, it further redshifts and decreases in
intensity. An isoemissive point is clearly observed on the fluorescence
emission spectra of PF/FLx as a function of fluorenone content, showing
that the new emission band is formed at the expense of PF. We propose
the formation of an intramolecular charge transfer complex (ICTC)
between PF units and 9-fluorenone to explain the appearance of the new
emission band. Global analysis of time resolved fluorescence decays
collected at 415 nm (PF emission) and 580 nm (the ICTC emission) show
that three exponentials are generally needed to achieve excellent fits.
Two of the components (420 ps and 6.5 ns) are independent of
9-fluorenone fraction. A further fast component is strongly dependent
on fluorenone fraction and ranges between 280 and 70 ps. This component
appears as a decay time at 415 nm and as a rise time at 580 nm and is
ascribed to the migration of exciton to quenching sites (formation of
intramolecular CT complex or exciton ionization at CT complex). A
kinetic mechanism involving three different kinetic species, quenched
PF units kinetically coupled with the ICTC complex, and unquenched PF
units is proposed to explain the experimental data and the quenching
rate constant is obtained, k(1)congruent to10(11) s(-1). This is an
experimental measurement of the intrachain exciton hopping rate. (C)
2005 American Institute of Physics.