Related Experiment Video
Updated: Aug 6, 2026
09:11
Raman and IR Spectroelectrochemical Methods as Tools to Analyze Conjugated Organic Compounds
Published on: October 12, 2018
Disentangling Polymorphism, Texture, and Molecular Orientation in TIPS-Pentacene Thin Films by Polarized Raman
Martina Zangari1, Francesco Stancari2, Tommaso Salzillo1
1Department of Industrial Chemistry "Toso Montanari" & INSTM-UdR Bologna, University of Bologna, Via P. Gobetti 85, Bologna 40129, Italy.
ACS Applied Optical Materials
|August 5, 2026
Summary
Bar-assisted meniscus shearing creates oriented organic semiconductor films without new polymorphs. This method, using X-ray diffraction and Raman spectroscopy, helps distinguish crystal structure, texture, and molecular orientation for better charge transport understanding.
Area of Science:
- Materials Science
- Organic Electronics
- Solid-State Physics
Background:
- Thin-film processing significantly impacts organic semiconductor crystal structures.
- Disentangling polymorphism, texture, and molecular orientation is crucial for charge transport.
- 6,13-bis-(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) is a model organic semiconductor.
Purpose of the Study:
- To investigate the structural properties of TIPS-pentacene thin films prepared by bar-assisted meniscus shearing.
- To determine if this processing method induces new polymorphs or alters existing structures.
- To establish effective methods for resolving structure, texture, and orientation in organic semiconductor films.
Main Methods:
- Preparation of highly oriented TIPS-pentacene thin films using bar-assisted meniscus shearing.
- Characterization via grazing-incidence X-ray diffraction (GIXD) for texture analysis.
- Spectroscopic analysis using polarized Raman spectroscopy.
- Theoretical validation through periodic first-principles calculations (density functional theory).
Main Results:
- Bar-assisted meniscus shearing yields TIPS-pentacene films adopting the bulk Form I crystal structure.
- The processing induces pronounced out-of-plane and in-plane textures, not new polymorphs.
- GIXD confirmed film texture, while polarized Raman spectroscopy and DFT calculations supported the Form I assignment.
- Low-frequency vibrational modes in TIPS-pentacene exhibit mixed character, sensitive to packing.
Conclusions:
- Bar-assisted meniscus shearing is suitable for creating highly ordered TIPS-pentacene films with controlled texture.
- Polarized Raman spectroscopy, GIXD, and DFT calculations effectively differentiate polymorphs, texture, and orientation.
- This combined approach provides a robust method for analyzing complex organic semiconductor thin films.
Related Concept Videos
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...
01:20¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
01:15¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
02:05Prochirality
The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
01:18Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...