Jump to main content
Jump to site search
Access to RSC content Close the message box

Continue to access RSC content when you are not at your institution. Follow our step-by-step guide.



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

Author affiliations

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

Back to tab navigation

Supplementary files

Article information


Submitted
21 Jun 2020
Accepted
31 Jul 2020
First published
21 Aug 2020

J. Mater. Chem. C, 2020, Advance Article
Article type
Paper

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, Advance Article , DOI: 10.1039/D0TC02945A

Social activity

Search articles by author

Spotlight

Advertisements