Issue 43, 2020

Engineering functionalized low LUMO [1]benzothieno[3,2-b][1]benzothiophenes (BTBTs): unusual molecular and charge transport properties

Abstract

Diacene-fused thienothiophenes (DAcTTs) have provided an excellent π-framework for the development of high mobility p-type molecular semiconductors in the past decade. However, n-type DAcTTs are rare and their electron transport characteristics remain largely unexplored. Herein, a series of functionalized low LUMO (lowest unoccupied molecular orbital) [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based small molecules, D(C7CO)-BTBT, C7CO-BTBT-CC(CN)2C7, and D(C7CC(CN)2)-BTBT, have been developed. Detailed structural, physicochemical, optoelectronic, and single-crystal characterization were performed. The new molecules exhibit large optical band gaps (∼2.8–3.1 eV) and highly stabilized (−ΔELUMO = 1.2–1.4 eV)/π-delocalized LUMOs as compared to p-type DAcTTs. Symmetric functionalization is found to be important to enable strong intermolecular interactions in the solid-state. All molecules exhibit alternately stacked layers of “F–BTBT–F” and “S” (F: functional group/S: substituent) with strong herringbone-like interactions (2.8–3.6 Å distances) between π-cores. While carbonyls, regardless of the substituent, adopt nearly coplanar π-backbones with BTBT, dicyanovinylenes are found to be twisted (47.5°). The conformational difference at the molecular level has unusual effects on the π-electron deficiencies, frontier molecular orbital energetics, thermal/photophysical properties, and π-electronic structures. Dicyanovinylenes at the 2,7 positions, despite twisted conformations, are shown for the first time to yield good electron transport in DAcTTs. The D(C7CC(CN)2)-BTBT thin film exhibits large 2D plate-like crystalline grains (∼1–2 μm sizes) of terraced islands and becomes a rare example of an n-type DAcTT in organic field-effect transistors (OFETs). Although a stabilized/π-delocalized LUMO, largely governed by functional groups and intramolecular twists, is essential for electron transport, our findings suggest that it should be combined with proper substituents to yield a favorable three-dimensional BTBT/functional group π-electronic structure and a low intramolecular reorganization energy. Combined with our first n-type DAcTT semiconductor D(PhFCO)-BTBT, a molecular library with systematically varied chemical structures has been studied herein for the first time for low LUMO DAcTTs. The molecular engineering perspectives presented in this study may give unique insights into the design of novel electron transporting thienoacenes for unconventional optoelectronics.

Graphical abstract: Engineering functionalized low LUMO [1]benzothieno[3,2-b][1]benzothiophenes (BTBTs): unusual molecular and charge transport properties

Supplementary files

Article information

Article type
Paper
Submitted
21 iyn 2020
Accepted
31 iyl 2020
First published
21 avq 2020

J. Mater. Chem. C, 2020,8, 15253-15267

Engineering functionalized low LUMO [1]benzothieno[3,2-b][1]benzothiophenes (BTBTs): unusual molecular and charge transport properties

R. Ozdemir, K. Ahn, İ. Deneme, Y. Zorlu, D. Kim, M. Kim and H. Usta, J. Mater. Chem. C, 2020, 8, 15253 DOI: 10.1039/D0TC02945A

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements