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


Abstract

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

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