Photoluminescence Intensity Fluctuations and Electric‐Field‐Induced Photoluminescence Quenching in Individual Nanoclusters of Poly(phenylenevinylene)

Abstract

Substantial fluctuations of the fluorescence intensity have been detected for single clusters of poly(phenylenevinylene) containing more than 75 polymer chains or 30,000 monomer units. To the best of our knowledge, this is the first time such fluctuations (which resemble the "blinking" effect in single-molecule fluorescence) have been reported for such a large molecular ensemble containing several macromolecules. Together with the distinct jumps, smooth fluctuations of the fluorescence intensity, with characteristic times from milliseconds to seconds, were observed. This fact distinguishes the fluorescence behaviour of the polymer clusters from that of other multichromophoric systems such as the single chains of conjugated polymers reported in the literature. The consecutive or simultaneous switching of one or several emitting sites from the "on" to "off" state does not explain the character of the fluctuations observed. We suggest that the quenching of the light-emitting exciton by a long-lived species, such as, for example, polarons, plays an important role in these unusual fluctuations. Electric field induced fluorescence quenching differs significantly for different clusters. It is proposed that this fluorescence was mainly quenched by polarons injected from the electrodes in the presence of an electric field. The specific behaviour of each cluster is explained by suggesting a different position of the clusters with respect to the electrodes.

Single particle spectroscopy on composite MEH-PPV/PCBM nanoparticles

“…The hole has a quenching radius in excess of 10 nm, which is on the same length scale as the nanoparticle dimensions. Similar observations have also been made in bulk films and aggregates [48,49].…”

Fluorescence blinking in MEH-PPV single molecules at low temperature

“…Indeed, an estimate of the quenching radius in case of Fo¨rster energy transfer to polarons is around 4 nm [12]. But a stretched MEH-PPV chain with a mass of 100000 units has a length of about 230 nm.Thus, in case (i) the polymer chains must have a collapsed conformation with characteristic sizes of at most a few nanometers.…”

“…However, the nature of the quencher and quenching mechanism are not understood. Among possible candidates charged species [7][8]12] and triplet states [13] can be pointed out. It is agreed that polymer conformation plays a very important (if not crucial) role in the blinking behavior.…”

Correlation between spectroscopic and morphological properties of composite P3HT/PCBM nanoparticles studied by single particle spectroscopy

“…These nanoparticles are an intermediate system between bulk films and single molecules, and limit the number of molecules (a few to a few tens of molecules) under investigation while maintaining the required functionality as found for the bulk material. This results in a material system that is representative of the bulk, but simplified enough to be able to complete studies that relate material function to properties at the molecular level [18][19][20][21][22]. In addition, certain processes that would go unnoticed in bulk measurements will be detected in nanoparticle samples by the single particle spectroscopy approach due to reduction of the heterogeneity based on both sample and methodology.…”