Related Experiment Video
Updated: Jul 11, 2026
09:11
Raman and IR Spectroelectrochemical Methods as Tools to Analyze Conjugated Organic Compounds
Published on: October 12, 2018
Raman spectroscopy of intermolecular charge transfer complex between a conjugated polymer and an organic acceptor
V V Bruevich1, T Sh Makhmutov, S G Elizarov
1Faculty of Physics and International Laser Center, Lomonosov Moscow State University, Moscow 119992, Russia.
The Journal of Chemical Physics
|September 18, 2007
Summary
Researchers investigated charge transfer complexes (CTCs) between MEH-PPV and TNF using spectroscopy. They found evidence of electron transfer and structural changes in MEH-PPV, indicating CTC formation in both films and solutions.
Area of Science:
- Materials Science
- Polymer Chemistry
- Spectroscopy
Background:
- Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is a conducting polymer with potential applications in organic electronics.
- Charge transfer complex (CTC) formation can significantly alter the electronic and optical properties of organic materials.
Purpose of the Study:
- To investigate the formation and characteristics of intermolecular donor-acceptor charge transfer complexes (CTCs) between MEH-PPV and 2,4,7-trinitrofluorenone (TNF).
- To understand the impact of CTC formation on the molecular structure and electronic properties of MEH-PPV.
Main Methods:
- Raman spectroscopy to analyze vibrational modes and structural changes in MEH-PPV.
- Optical absorption spectroscopy to detect the formation of CTCs and their spectral signatures.
Main Results:
- The formation of a CTC between MEH-PPV and TNF was confirmed by the appearance of a new absorption band and changes in MEH-PPV's Raman spectra.
- A low-frequency shift in a key MEH-PPV Raman band indicated partial electron transfer (approximately 0.2e(-)) from MEH-PPV to TNF.
- Experimental data were consistent in both solid films and solutions, suggesting CTC formation occurs in both states.
Conclusions:
- Intermolecular CTCs form between MEH-PPV and TNF in the electronic ground state.
- The polymer segments involved in CTCs become more planar, but their conjugation length remains unchanged.
- The stoichiometry of the CTC can vary, with a suggested composition of MEH-PPV:TNF=1:X, where X ≤ 0.5 per MEH-PPV monomer unit.
Related Concept Videos
01:32UV–Vis Spectroscopy of Conjugated Systems
Organic compounds with conjugated double bonds show strong absorption features in the UV–visible region of the electromagnetic spectrum attributed to π → π* electronic excitations. Generally, a UV–vis absorption spectrum is recorded as a plot of absorbance vs wavelength. The wavelength of maximum absorbance, which manifests as a peak in the absorption spectrum, is denoted as λmax.
One of the factors influencing λmax is the extent of conjugation in the...
One of the factors influencing λmax is the extent of conjugation in the...
01:20Raman Spectroscopy: Overview
The underlying principle of Raman spectroscopy is based on the interaction between light and matter, specifically molecules' inelastic scattering of photons. When a monochromatic beam of light, typically from a laser source, interacts with a sample, most scattered light has the same frequency as the incident light. This is known as Rayleigh scattering.
However, a small fraction of the scattered light exhibits a frequency shift due to the exchange of energy between the incident photons and the...
However, a small fraction of the scattered light exhibits a frequency shift due to the exchange of energy between the incident photons and the...
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:29IR and UV–Vis Spectroscopy of Aldehydes and Ketones
Infrared spectroscopy, also known as vibrational spectroscopy, is mainly used to determine the types of bonds and functional groups in molecules. In aldehydes and ketones, the carbonyl (C=O) bond shows an absorption around 1710 cm-1. The C=O bond vibration of an aldehyde occurs at lower frequencies than that of a ketone. In addition to the C=O absorption in an aldehyde, the aldehydic C–H bond also gives two peaks in the 2700–2800 cm-1 range. This absorption, coupled with the C=O stretching, is...
01:16UV–Vis Spectroscopy: Molecular Electronic Transitions
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this process,...
01:28IR and UV–Vis Spectroscopy of Carboxylic Acids
In IR spectroscopy of carboxylic acids, the C=O bond shows a characteristic band between 1710 and 1760 cm⁻¹, and the O–H bond exhibits a broad band between 2500 and 3300 cm⁻¹.
However, the stretching absorptions for the C=O bond vary depending on the structure of carboxylic acids. The C=O bond of the free carboxylic acids shows a higher stretching frequency, 1760 cm−1, while H-bonded carboxylic acids (dimers) exhibit stretching absorptions at a lower frequency, 1710 cm−1. The C=O bond of the...
However, the stretching absorptions for the C=O bond vary depending on the structure of carboxylic acids. The C=O bond of the free carboxylic acids shows a higher stretching frequency, 1760 cm−1, while H-bonded carboxylic acids (dimers) exhibit stretching absorptions at a lower frequency, 1710 cm−1. The C=O bond of the...