Directional Crystallization from the Melt of an Organic p-Type and n-Type Semiconductor Blend

Abstract

Directional crystallization from the melt has been used as a tool to grow parallel crystalline stripes of p-and n-type molecular semiconductors. To start, the phase behavior of 2,7dioctyl[1]benzothieno [3,2-b][1]benzothiophene (C8-BTBT-C8): tetracyanoquinodimethane (TCNQ) blends (molar ratio from 20:1 to 1:1) has been investigated by variable-temperature X-ray diffraction, differential scanning calorimetry, and polarized optical microscopy. The partial charge transfer between the C8-BTBT-C8 donor and the TCNQ acceptor as a function of temperature has been studied. Blends of 10:1 and 20:1 have been selected for directional crystallization because they show similar thermotropic and phase behavior comparable to that of pure C8-BTBT-C8. Directional crystallization results suggest that moderate cooling rates (6 and 12 °C min −1 ) leads to a digitated growth mode that gives rise to parallel crystalline stripes of C8-BTBT-C8 and C8-BTBT-C8-TCNQ charge-transfer complexes (C8-BTBT-C8-TCNQ CT), as confirmed by confocal Raman imaging. X-ray diffraction reveals high preferential orientation and good in-plane alignment for both C8-BTBT-C8 and C8-BTBT-C8-TCNQ CT crystallites.

Charge transfer complexes of a benzothienobenzothiophene derivative and their implementation as active layer in solution-processed thin film organic field-effect transistors

“…The latter cannot be explained by the mismatch of the highest occupied molecular orbital (HOMO) of the donor with the lowest unoccupied molecular orbital (LUMO) of the acceptor, 25 since CT complexes with TCNQ have been reported for other BTBT derivatives, with even deeper HOMO level. 6,20,21,[26][27][28] Both CT complexes, (C 8 O-BTBT-OC 8 )(F 2 TCNQ) and (C 8 O-BTBT-OC 8 )(F 4 TCNQ), crystallize as isomorphous in the triclinic P% 1 space group (see Table S1 for details and Fig. S1, ESI †), and feature extended stacks, running along the a-axis, in which molecules of the donor C 8 O-BTBT-OC 8 alternate with the corresponding acceptor TCNQ-derivative in an Á Á ÁAÁ Á ÁDÁ Á ÁAÁ Á ÁDÁ Á Á fashion (Fig.…”

“…Additionally, it is worth noting how both (C 8 O-BTBT-OC 8 )(F 2 TCNQ) and (C 8 O-BTBT-OC 8 )(F 4 TCNQ) display a remarked structural resemblance with other CT complexes made up of alkylated benzothienobenzothiophene and TCNQ derivatives, which were previously reported as promising candidates for the development of OSCs. 6 Raman and Infrared (IR) spectroscopy are non-destructive techniques very useful for the characterisation of CT complexes Scheme 1 Molecular structures of the donor (C 8 O-BTBT-OC 8 ) and acceptor (F 2 TCNQ and F 4 TCNQ) compounds, and HOMO (blue) and LUMO (red) energy levels for C 8 O-BTBT-OC 8 , F 2 TCNQ, and F 4 TCNQ. 22,23 The LUMO levels of the acceptor molecules were estimated by Inverse Photoemission Spectroscopy (IPES).…”

“…The latter cannot be explained by the mismatch of the highest occupied molecular orbital (HOMO) of the donor with the lowest unoccupied molecular orbital (LUMO) of the acceptor, 25 since CT complexes with TCNQ have been reported for other BTBT derivatives, with even deeper HOMO level. 6,20,21,26–28…”

“…1,2 For many decades CT complexes were intensively investigated in order to establish guidelines to design materials exhibiting high roomtemperature mobility or superconductivity. 3 However, in the more recent years, the focus has also been placed on the development of more technologically relevant applications deploying such CT complexes, [4][5][6] including thermoelectrics, 7 photoconductors, 8,9 strain sensors, 10 light detectors, 11 ferroelectrics 12 or organic field-effect transistors (OFETs), where CT complexes can act as organic metals 13,14 or organic semiconductors. 15,16 The separate D or A units in a CT complex typically can act as unipolar (p and n, respectively) organic semiconductors when implemented in an OFET.…”

Memory Effect and Crystallization of (R, S)-2-Chloromandelic Acid Glass

“…As part of our research dedicated to the nucleation and growth of organic crystals from the melt state in direct contact with rigid substrates, − this work presents the case of 2-chloromandelic acid (2-ClMA) that exists as R and S enantiomers, shown in Figure S1. ( R )-2-ClMA is an important pharmaceutical intermediate to produce ( S )-clopidogrel, an antiplatelet agent used to treat coronary artery and vascular disease. , Recently, racemic ( R , S )-2-chloromandelic acid was identified as a metastable conglomerate (form γ) by He et al , and Lorenz et al The conglomerate can be obtained from freeze-drying an aqueous solution, crystallization from polar solvents, or undercooled liquid.…”