Effect of PCBM Concentration on Photoluminescence Properties of Composite MEH‐PPV/PCBM Nanoparticles Investigated by a Franck–Condon Analysis of Single‐Particle Emission Spectra

Abstract

The emission of composite conjugated polymer (MEH-PPV)/fullerene (PCBM) nanoparticles is investigated by single particle spectroscopy (SPS), and changes in vibronic structure with nanoparticle composition are evaluated by means of a detailed Franck-Condon analysis. Consistent with previous reports we find that the emission spectra can be modeled as the superposition of two types of emitters, one with aggregate character and one with molecular character. Major findings from the fitting of the SPS data to a Franck-Condon model are that 1) the occurrence of each of the two types of emitters changes with nanoparticle composition to the point that no aggregate emitters are detected (at 50 wt% PCBM), 2) at the highest PCBM doping levels (75 wt% PCBM) aggregate emitters reappear due to nanoscale phase separation in the composite nanoparticles, 3) the molecular emitters show small Huang-Rhys factors that increase with PCBM doping, indicative of extensive delocalization and exciton migration that is reduced by the disorder introduced in the polymer material by PCBM doping and 4) the aggregate emitters show large Huang-Rhys factors, indicative of the localized nature of these energy trap sites, with a broad distribution of values of these Huang-Rhys factors. The latter observation suggests a broad heterogeneous distribution of aggregate morphologies in blended conducting polymer materials, which can be attributed to variations in polymer chain folding and stacking at the aggregate sites. The reported results obtained by the SPS approach show how blending conjugated polymers with fullerenes at various doping levels induces changes in interchain interactions and aggregate site density even at length scales below a few tens of nanometers that affect conjugated polymer material properties, an observation that has gone unnoticed in bulk studies of blended conjugated polymer films.

Single nanoparticle of organic p-type and n-type hybrid materials: nanoscale phase separation and photovoltaic effect

“…The S factor is defined as S ¼ I 0-1 /I 0-0 , where I 0-1 and I 0-0 are the absorption intensities of the 0-1 and 0-0 transitions, corresponding to the peaks at 555 and 606 nm, respectively, and indicates the variation in the p-conjugation length due to conformational disorder (a low S value indicates a longer pconjugation length). 20 The S values for the annealed hybrid NPs were smaller than those of the non-annealed hybrid NPs for all the PCBM concentrations, as shown in Fig. 3(b).…”

Photoinduced Cation Translocation in a Calix[4]biscrown: Towards a New Type of Light‐Driven Molecular Shuttle

“…SMS samples were prepared by spin‐coating a 2 wt.‐% PMMA solution containing an appropriate concentration of conjugated polymer onto a clean cover slide, followed by thermal deposition of aluminum film approximately 200 nm thick to prevent fast photobleaching during the experiments. The SMS experimental apparatus was a home‐built sample‐scanning confocal microscope that has been described elsewhere 26, 27. The data reported herein were recorded under laser excitation at 488 nm from an argon‐ion laser (Melles Griot 43 series).…”

Single‐Molecule Spectroscopy and AFM Morphology Studies of a Diblock Copolymer Consisting of Poly(3‐hexylthiophene) and Fullerene

“…The SMS experimental apparatus was a home-built sample-scanning confocal microscope that has been described elsewhere. [26,27] The data reported herein were recorded under laser excitation at 488 nm from an argon-ion laser (Melles Griot 43 series). The pixel dwell times for imaging were 20 ms. Single-molecule emission spectra were collected using an Andor iXon EMþ DU-897 back-illuminated charge-coupled device coupled to a spectrograph (PI Acton SP-2156).…”