Evidence of temperature dependent charge migration on conjugated segments in poly-p-phenylene vinylene and single-walled carbon nanotubes composite films

Abstract

We present new results of temperature dependence of photoluminescence spectra carried out on poly-p-phenylene vinylene (PPV) and on PPV composite films with single-walled carbon nanotubes. By performing studies at different temperatures (87 and 300 K), we show that a distribution of conjugated PPV segments is needed to interpret experimental data. At the microscopic scale, such a distribution corresponds to the morphological picture of poorly packed short chain segments and well-packed ordered long chain segments. Within this scheme, a new interpretation emerges for explaining the specific behavior of the photoluminescence bands. In particular, the two most intense components of the photoluminescence spectra of PPV thermally converted at 300 degrees C (2.23 and 2.43 eV at 300 K) change drastically their relative intensity when the observation temperature decreases. This effect is interpreted as due to the inhibition of charge migration to longer segments and to radiative recombination occurring mainly on n = 5 conjugated segments.

Grafting of oligo-N-vinyl carbazole on single walled carbon nanotubes

“…Besides, the two PL bands situated at lower wavelengths change mutually their relative intensities as it is reported for PPV/SWNTs [50]. This change implies the formation of new luminescent centre which corresponds probably to the defect related to the covalent bonding of SWNTs, as envisaged in the case of polystyrene functionalized SWNTs [51].…”

Influence of Single-Walled Carbon Nanotubes Enriched in Semiconducting and Metallic Tubes on the Vibrational and Photoluminescence Properties of Poly(para-phenylenevinylene)

“…were purchased from NanoIntegris. The strategy used for the synthesis of the PPV/SWNTs composite involves (i) the preparation of three suspensions of M-SWNTs, S-SWNTs, and (M+S)-SWNTs that have ∼2 mg of CNTs in 2 mL of toluene under ultrasonication for 10 min; (ii) the deposition of the M-SWNTs, S-SWNTs, and (M+S)-SWNTs films onto rough Au supports with an area of 1 cm 2 (the CNT film thickness is estimated using the protocol described in ref 18 and by knowing that the density of the M-SWNTs, S-SWNTs, and (M +S)-SWNTs was equal to 1.13, 19 2.23, 19 and 1.337 20 g/cm 3 , respectively); and (iii) the preparation of a solution of 0.02 M TBPX and 0.1 M tetrabuthylammonium bromide (TBAB) in dimethylformamide (DMF). PPV and its composites were synthesized using cyclic voltammetry in a conventional threeelectrodes, one-compartment cell.…”

“…The interest in poly­(para-phenylenevinylene)/carbon nanotubes (PPV/CNT) composites began in 1999 and was motivated by their great potential for applications in the field of photovoltaic devices. The synthesis method that is currently used for composites based on PPV and CNTs (either multiwalled carbon nanotubes (MWNTs) or single-walled carbon nanotubes (SWNTs)) is the thermal conversion of the PPV precursor solution (hereafter labeled PPV PS) containing different weight percentages of CNTs. , For a better understanding of the physical properties of this composite material, various optical studies have been reported: Stokes and anti-Stokes photoluminescence (PL), , electroluminescence, ultraviolet–​visible–​near-infrared (UV–vis–NIR) absorption, photoconductivity, resonant/nonresonant Stokes/anti-Stokes Raman scattering , and absorption middle infrared (IR) spectroscopy . The main highlights of these studies are the following: (i) SWNTs induce a percolation regime in the PPV matrix, beginning at a weight percentage of SWNTs of ≈2% .…”

“…(iii) The PL spectra reveal that SWNTs play a role in inhibiting the complete thermal conversion of the PPV precursor due to the functionalization of SWNTs with PPV macromolecular chains (MCs) of different length. (iv) SWNTs play the role of a PPV PL quenching agent. − (v) Nonresonant/resonant Raman spectroscopy , demonstrates that a noncovalent functionalization of SWNTs with PPV occurs during the thermal conversion of the PPV PS containing different weights of SWNTs. (vi) A modification of the angle of the IR active transition dipole moment of the phenyl ring C–H in the out-of-plane vibrational mode, situated at ∼835 cm –1 , was reported in the case of the samples obtained by the thermal conversion of the PPV PS containing different weights of SWNTs .…”

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

“…Moreover, a new vibronic structure apperas at lower energy side of the emission spectrum centered at 499 nm (2.48 eV) is observed in the case of the chloroform solvent. In fact, in both cases an energy transfer is occured as depicted by the mutual change of PL intensity between the two PL bands situated at lower wavelengths as it is reported for PPV/SWNTs (Mulazzi et al, 2006). This change implies the formation of new luminescent centre which corresponds probably to the defect related to the covalent bonding of SWNTs In fact, the band observed at 499 nm can be the consequence of annealing treatment or of the SWNTs addition.…”