Remarkable Photophysics and Amplified Quenching of
Conjugated Polyelectrolyte Oligomers
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Abstract
We report the photophysics and fluorescence
quenching of a series
of monodisperse, anionic π-conjugated oligomers that are molecularly
dissolved in aqueous solution. These structurally well-defined oligomers
feature oligo(phenylene ethynylene) backbones with two −CH<sub>2</sub>COO<sup>–</sup> units on each repeat unit, with overall
lengths of 5, 7, and 9 repeats. The ionic oligomers display a structured
fluorescence band with high quantum efficiency in water, in contrast
to the low fluorescence quantum efficiency and pronounced aggregation
displayed by structurally similar oligomeric and polymeric (phenylene
ethynylene) conjugated polyelectrolytes studied previously. Stern–Volmer
(SV) fluorescence quenching studies using cationic charge- and energy-transfer
quenchers reveal that all of the oligomers give rise to SV quenching
constants (<i>K</i><sub>SV</sub>) in excess of 10<sup>6</sup> M<sup>–1</sup>, with values increasing with oligomer length,
consistent with the amplified quenching effect. The amplified quenching
effect is proposed to occur due to the formation of comparatively
small oligomer aggregates