CC BY 4.0 · Organic Materials 2023; 5(01): 72-83
DOI: 10.1055/a-2020-0308
Organic Materials in India
Original Article

Exploring Indeno[2,1-c]fluorene Antiaromatics with Unsymmetrical Disubstitution and Balanced Ambipolar Charge-Transport Properties

a   Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India
b   Department of Electrical Engineering, School of Engineering, Shiv Nadar Institution of Eminence, Gautam Buddha Nagar, Uttar Pradesh 201314, India
a   Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India
b   Department of Electrical Engineering, School of Engineering, Shiv Nadar Institution of Eminence, Gautam Buddha Nagar, Uttar Pradesh 201314, India
a   Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India
› Author Affiliations


Unsymmetrically disubstituted antiaromatic indenofluorene (IF), in comparison to aromatic pentacene counterpart with unsymmetrical disubstitution, was rare in the literature until our recent report on indeno[1,2-b]fluorene and indeno[2,1-a]fluorene. Described herein is a straightforward access to unsymmetrically disubstituted indeno[2,1-c]fluorenes bearing mesityl at one apical carbon and C6F5, 3,5-(CF3)2C6H3, and CCSii-Pr3 at the other apical carbon, including 4-methoxyphenyl/3,5-(CF3)2C6H3 push/pull substitution at the apical carbons with appreciable orbital density, and a previously unknown symmetrically C6F5-disubstituted [2,1-c]IF. The electronic properties of the unsymmetrical derivatives lie halfway in between the two symmetrical counterparts, while the 4-methoxyphenyl derivative showed the smallest HOMO–LUMO energy gap and near-infrared absorption with intramolecular charge transfer character. Single-crystal analyses showed 1D-columnar stacks for the unsymmetrical motif with the C6F5 units co-facially π-stacked with the IF core, whereas symmetrically C6F5-disubstituted [2,1-c]IF, with a low-lying LUMO, showed intermolecular π–π stacks between the IFs that resulted in good electron mobility (µ e = 8.66 × 10−3 cm2 · V−1 · s−1) under space charge limited current measurements. Importantly, balanced ambipolar charge-transport behaviour could be extracted for an IF series with symmetrical/unsymmetrical substitutions, in comparison to its π-contracted pentalene congener.

Publication History

Received: 16 October 2022
Received: 14 December 2022

Accepted after revision: 25 January 2023

Accepted Manuscript online:
27 January 2023

Article published online:
15 February 2023

© 2023. The authors. This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (

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