Mobility versus Alignment of a Semiconducting π‑Extended Discotic Liquid-Crystalline Triindole Constanza Ruiz, †,‡ Upendra K. Pandey, §,∥ Roberto Termine, § Eva M. García-Frutos, † Guzma ́ n Ló pez-Espejo, ⊥ Rocío Ponce Ortiz, ⊥ Wei Huang, ‡ Tobin J. Marks, ‡ Antonio Facchetti, ‡ M. Carmen Ruiz Delgado, ⊥ Attilio Golemme, § and Berta Gó mez-Lor* ,† † Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049, Madrid, Spain ‡ Department of Chemistry and the Materials Research Center, the Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States § LASCAMM CR-INSTM, CNR-NANOTEC Lab LiCryL, Dipartimento di Fisica, Universita ̀ della Calabria, 87036 Rende, Italy ∥ Interdisciplinary Centre for Energy Research, Indian Institute of Science, Bangalore, 560012, India ⊥ Department of Physical Chemistry, University of Ma ́ laga, 29071, Ma ́ laga, Spain * S Supporting Information ABSTRACT: The p-type semiconducting properties of a tripheny- lene-fused triindole mesogen, have been studied by applying two complementary methods which have different alignment require- ments. The attachment of only three flexible alkyl chains to the nitrogen atoms of this π-extended core is sufficient to induce columnar mesomorphism. High hole mobility values (0.65 cm 2 V −1 s −1 ) have been estimated by space-charge limited current (SCLC) measurements in a diode-like structure which are easily prepared from the melt, rendering this material a good candidate for OPVs and OLEDs devices. The mobility predicted theoretically via a hole- hopping mechanism is in very good agreement with the experimental values determined at the SCLC regime. On the other hand the hole mobility determined on solution processed thin film transistors (OFETs) is significantly lower, which can be rationalized by the high tendency of these large molecules to align on surfaces with their extended π-conjugated core parallel to the substrate as demonstrated by SERS. Despite the differences obtained with the two methods, the acceptable performance found on OFETs fabricated by simple drop-casting processing of such an enlarged aromatic core is remarkable and suggests facile hopping between neighboring molecular columns owing to the large conducting/isolating ratio found in this discotic compound. KEYWORDS: organic semiconductors, discotic liquid-crystals, OFETS, SCLC measurements, hole mobility ■ INTRODUCTION The field of organic electronics has evolved impressively in the past few years and the first device generation based on organic semiconductors has reached the market. 1, 2 The major contribution advancing this field have been associated with the development of organic semiconductors exhibiting high charge carrier mobility. However, finding organic semi- conductors with the proper balance between mobility and processability, remains challenging. In this context discotic liquid crystals, constituted by an aromatic central core surrounded by flexible alkyl tails, are among the most promising candidates. 3−5 In the columnar mesophases induced by discotic mesogens the aromatic cores are strongly interacting ensuring an uniaxial pathway for efficient charge carrier transport while the soft and self-repairing nature of these materials facilitates their easy processing and the realization of defect free domains over large areas. 6−10 Because of their characteristic molecular structure consisting of a π-conjugated conducting core surrounded by electrically insulating substituents, charge transport in discotic liquid crystals is highly anisotropic and a precise control of the orientation of the columnar axis on the substrate is therefore essential to optimize charge transport. 11,12 This high dependence of the electrical performance on the degree of columnar alignment represents a serious drawback for application of discotic mesogens in several optoelectronic devices by simple solution-processing techniques. Although the uniform macroscopic orientation of columns on different substrates has been successfully achieved via different strategies such as the application of electric 13,14 or magnetic fields, 12,15 use of surface modifiers, 16,17 and confinement effects 18,19 among others, to date solutions vary from material to material and are complicated by the fact that each type of device has Received: May 26, 2016 Accepted: September 19, 2016 Research Article www.acsami.org © XXXX American Chemical Society A DOI: 10.1021/acsami.6b06241 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX