Optical Properties of Poly(para-phenylene Vinylene) and Single-Walled Carbon Nanotube Composite Films:  Effects of Conversion Temperature, Precursor Dilution, and Nanotube Concentrations

Abstract

Optical absorption, photoluminescence, and Raman scattering spectra of poly(para-phenylene vinylene) (PPV) and single-walled carbon nanotube (SWNT) composite films are investigated at room temperature. Samples have been prepared at different precursor conversion temperatures, T c , (300, 180,and 120°C) and with SWNT mass concentrations from x) 0% up to 64%. In each sample, we observe drastic changes in all optical absorption spectra of PPV and composite films. In particular, after conversion at T c) 120°C, PPV samples exhibit photoluminescence (PL) with a new feature at about 2.55 eV together with less-intense ones at about 2.37 and 2.20 eV, respectively. The most-intense at 2.55 eV is due to a radiative recombination on the shorter conjugated segments and interpreted from a theoretical model based on a distribution of conjugated lengths. This distribution, which allows an assignment of all PL peaks, is also able to explain all experimental data including Raman scattering and optical absorption spectra in a given sample. Also, further changes in PL and optical absorption spectra are observed by increasing the SWNT concentration in composite films converted at the same temperature. We have also investigated the effect of the dilution of the precursor polymer solution. From the theoretical analysis of the optical absorption, PL, and resonance Raman spectra, we show that PPV samples are characterized by a decrease of the effective conjugation lengths when the precursor dilution increases. All experimental data are explained well with a bimodal distribution model reflecting an effective inhomogeneity in the polymer as suggested already from morphological pictures issued in particular from X-ray data.

Photoluminescence properties of new PPV derivatives

“…The graft groups on the phenyl rings in the C 1-4 -PPV-ether are therefore expected to affect the planarity of the structure. Similar observations have been addressed by other authors [29,30]. They compared series of 3,6 carbazolenevinylene derivatives [31] and series of triphenylamine derivatives [32] with different groups and observed a faster PL decay for derivatives presenting a more non-planar conformation.…”

“…The standard PPV film is characterized by long conjugated segments organized in well packed regions (formed in aggregated area) where polymer chains are close to each other [29]. It was demonstrated in a previous publication that this aggregation play a role in the decay rates in PPV film [30]. Thus interchain interactions favor a fast migration of excitons providing a fast decay channel.…”

Electronic interaction in composites of a conjugated polymer and carbon nanotubes: first-principles calculation and photophysical approaches

“…A comparable behavior has been observed at the interface of PPV/MWCNT bilayers by Ago et al [29–30]. This trend is also similar to that of pristine PPV films fabricated from precursor solutions at low concentration or with decreasing conversion temperatures [11]. The inversion of the intensity ratio at x = 8% can be explained by the onset of formation of much shorter, conjugated segments with average repeat unit number 3 ≤ n u ≤ 5.…”

About Grafting of Single-Walled Carbon Nanotubes on the Oligo-N-Vinyl Carbazole and Copolymer Involving N-Vinylcarbazole and Hexylthiophene

“…Compared to the pristine PVK-3HT, the increase of SWNTs weight concentration progressively induces a faster decays time. A comparable behavior has been observed on the transient decays time of the prepared composite of PPV and SWNTs (Massuyeau et al, 2007). This behavior supports the hypothesis that SWNTs in the composite present a good network for the charge migration from and their presence facilate also the separation process.…”

“…However, the band at 430 nm shows a sudden decrease when adding SWNTs and undergoes a continuously blueshiftwing, reflecting that there is a shortness of the effective conjugation length of these blocks (Wéry et al, 2003). Although, there is no significant changes observed in optical absorption spectra when increasing SWNTs weight concentration due to the already reached percolation threshold, the large amount of SWNTs either in grafted or not, or in isolated or bundled forms can influences the excitated states of the resulting composite (Massuyeau et al, 2007). Therefore, the luminescent properties must logically undergo a dependent evolution versus the SWNTs weight concentrations.…”