Atropisomeric Conjugated Diimides in Semiconductors

In a recent study published in the journal ACS Materials Letters, for the first time, researchers analyzed atropisomerism in 1,4,5,8-naphthalene tetracarboxylic diimides (NDIs) and 3,4:9,10-perylene tetracarboxylic diimides (PDIs) for application in thermally responsive organic semiconductors.

Study: Atropisomeric Conjugated Diimides: A Class of Thermally Responsive Organic Semiconductors. Image Credit: Macro photo/

These diimides have two stable conjugated forms at room temperature, namely Syn-conformers and anti-conformers.

The Syn and Anti conformers are interconvertible in a heated solution, but in the solid-state, only the Syn conformers can be converted into Anti conformers via thermal annealing.

The researchers found that, for organic field-effect transistors (OFETs), conversion of Syn-NDI into Anti-NDI exhibited a 100-fold improvement in electron mobility, whereas, for the conversion of Syn-PDI to Anti-PDI, the recorded improvement in electron mobility was 5000-fold. Also, all Anti-conformer semiconductors had similar order and magnitude of electron mobility irrespective of the amount of thermal annealing.

What is Atropisomerism?

Atropisomerism is a stereochemical phenomenon resulting from steric hindrance that restricts rotation about a single chemical bond, most commonly a σ-bond between two sp2 hybridized atoms. Atropisomers compounds feature stereogenic axes due to the restriction of rotation around chemical bonds such as Caryl-Caryl and Caryl-N. Depending on the rotational conformation, atropisomers can be divided into two types, namely S-shape divergent antirotamers and C-shape convergent syn-rotamers.

Moreover, atropisomers based on conjugated aromatic diimide derivatives such as 1,2,4,5-benzene tetracarboxylic diimides (BDI), NDI, and PDI show restricted rotation of the Caryl-Nimide bonds imposed by the steric hindrance of ortho-alkyl substituents with the imide carbonyls.

The compounds with larger polarity and smaller retention factor (Rf) values are assigned as Syn-NDI and Syn-PDI, in which the long dodecyl ortho-alkyl substituents are on the same side NDI/PDI core. Meanwhile, the compounds with lesser polarity and larger Rf values are assigned as Anti-NDI and Anti-PDI, in which the long dodecyl ortho-alkyl substituents are oriented to different sides of the NDI/PDI core.

Characterization of NDI and PDI Conjugate Conformers

All NDI and PDI-based conjugate atropisomers showed good solubility in common organic solvents, such as dichloromethane and chloroform. Thermogravimetric analysis (TGA) showed 5% weight loss at 419 and 426 °C for Syn-NDI and Anti-NDI, respectively.

More from AZoM: An Overview of Atom Chip Technology

Differential scanning calorimetry (DSC) plots for second heating and cooling cycles showed almost identical peak values for both Syn-NDI and Anti-NDI, indicating the same phase transitions. The UV−vis absorption spectra of Syn-NDI and Anti-NDI in dilute dichloromethane solution and the thin film state were also identical. 

In solution, the maximum absorption was at 580 nm, which red-shifted by 5nm for the thin films (solid-state). Furthermore, at 111°C and in a toluene solution, both Syn-NDI and Anti-NDI interconverted to each other at a fast rate. However, down at 80 °C, only Syn-NDI converted to Anti-NDI. The rotational energy barriers rates of pure Syn-NDI and Anti-NDI in toluene at 100 °C were 111.41 and 114.68 kJ/mol, respectively.

In contrast, the UV-vis absorption spectra of Syn-PDI and Anti-PDI showed differences in the thin film state with onset absorption wavelengths at 537 and 543 nm, respectively, indicating that there are obvious intermolecular interactions in the thin-film state. Additionally, the rotational energy barrier of both in toluene solution was similar at 100 °C. The conversion of Syn-PDI into Anti-PDI in a thin-film state was faster in the temperature range of 100−140 °C.

Effect of Thermal Annealing

The team fabricated bottom-gate top-contact (BGTC) OFETs with NDI- or PDI-based atropisomers as active layers and measured corresponding electron mobility at different annealing temperatures. The thin films of Syn-NDI showed average electron mobility on the order of 10−4 cm2.V−1. s−1, while for Anti-NDI it was at about 10−2 cm2. V−1.s−1.

After thermal annealing at 240 °C, the average electron mobility of Syn-NDI increased to 10−2 cm2. V−1.s−1, which was 100-fold higher than the value of the initial thin film. Similarly, when thin films of Syn-PDI were thermally annealed at 160 °C, the average electron mobility drastically increased from ~10−2 cm2.V−1. s−1 to 7.87 × 10−2 cm2.V−1.s−1.


To conclude, the researchers of the current study analyzed the application of atropisomerism behavior of NDIs and PDIs in a thermally responsive organic semiconductor. They found that the interconversion of NDI and PDI conjugates increased electron mobility by 10-fold and 5000-fold, respectively. The conjugate conversion was one-way in solid thin film state, but either-ways in solution state. Also, in contrast to NDI conjugates, PDI conjugates indicated intermolecular interactions in a thin-film state. This discovery can help develop multi-stimuli-responsive semiconductor devices.


Ge, C., Zhang, W., Tan, W., McNeill, C., Gao, X., Atropisomeric Conjugated Diimides: A Class of Thermally Responsive Organic Semiconductors, ACS Materials Letters, 2022, 4, 363-369.

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

Bismay Prakash Rout

Written by

Bismay Prakash Rout

Bismay is a technical writer based in Bhubaneshwar, India. His academic background is in Engineering and he has extensive experience in content writing, journal reviewing, mechanical designing. Bismay holds a Masters in Materials Engineering and BE in Mechanical Engineering and is passionate about science & technology and engineering. Outside of work, he enjoys online gaming and cooking.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Prakash Rout, Bismay. (2022, January 21). Atropisomeric Conjugated Diimides in Semiconductors. AZoM. Retrieved on March 24, 2023 from

  • MLA

    Prakash Rout, Bismay. "Atropisomeric Conjugated Diimides in Semiconductors". AZoM. 24 March 2023. <>.

  • Chicago

    Prakash Rout, Bismay. "Atropisomeric Conjugated Diimides in Semiconductors". AZoM. (accessed March 24, 2023).

  • Harvard

    Prakash Rout, Bismay. 2022. Atropisomeric Conjugated Diimides in Semiconductors. AZoM, viewed 24 March 2023,

Tell Us What You Think

Do you have a review, update or anything you would like to add to this news story?

Leave your feedback
Your comment type