Core Fluorination Enhances Solubility and Ambient Stability of an IDT‐Based n‐Type Semiconductor in Transistor Devices

Abstract

The synthesis of a novel fluorinated n-type small molecule based on an indacenodithiophene core is reported. Fluorination is found to have a significant impact on the physical properties, including a surprisingly dramatic improvement in solubility, in addition to effectively stabilizing the lowest-unoccupied molecular orbital energy (−4.24 eV). Single-crystal analysis and density functional theory calculations indicate the improved solubility can be attributed to backbone torsion resulting from the positioning of the fluorine group in close proximity to the strongly electron-withdrawing dicyanomethylene group. Organic thin-film transistors made via blade coating display high electron mobility (up to 0.49 cm 2 V −1 s −1 ) along with good retention of performance in ambient conditions.

n-Type organic semiconducting polymers: stability limitations, design considerations and applications

“…as expected with PTEG-1 70 ), long range order is achieved, and therefore mobility is increased. 71,72 However, where branched chains are required to impart sufficient solubility, they can significantly impede charge transport. 73 One solution is the introduction of a linear spacer between the backbone and the branching point, which maintains good close-contact distances and allows for solution-processability of the material.…”

The influence of alkyl group regiochemistry and backbone fluorination on the packing and transistor performance of N-cyanoimine functionalised indacenodithiophenes

“…29,[31][32][33][34] We recently reported that the functionalization of the bridgehead position of IDT with the strongly electron withdrawing dicyanomethylene group together with simultaneous fluorination of the central benzene ring resulted in a material with a low lying LUMO and promising n-type performance. 35 Unusually, we found that this material demonstrated improved solubility compared to the analogous nonfluorinated material, which appeared to result from the steric interactions between the fluorine and the dicyanomethylene group leading to a bowing of the structure.…”

“…2,7-Dihexyl-diFIDT-di(N(CN)) and 3,8-dihexyl-diFIDT-di(N(CN)) were synthesised following a modified literature procedure (Scheme 1). 36,40 The starting 2,7-dihexyl-diFIDT-di(O) was synthesised following our recently reported route, 35 and the isomeric 3,8dihexyl-diFIDT-di(O) was prepared by a modification of the route reported to the non-fluorinated analogue. 32 Thus, Stille crosscoupling of diethyl 2,5-dibromo-3,6-difluoroterephthalate ( [1]) with trimethyl(4-hexylthiophen-2-yl)stannane ([2]) using tetrakis (triphenylphosphine)palladium(0) afforded diethyl 2,5-difluoro-3,6-bis(4-hexylthiophen-2-yl)terephthalate ( [3]) in high yield (83%) after purification by silica gel chromatography.…”

“…This change in packing motif upon core fluorination is similar to that observed for the dicyanomethylene-containing analogue, 2,7-dihexyl-diFIDT-di(C(CN) 2 ), reported in our previous study. 35 There is co-facial packing of the conjugated core within a stack, along the a axis, with an interplanar stacking distance of 3.41 Å and a slipping distance of 3.24 Å (angle 43.61) (Fig. S22, ESI †).…”

“…39 In our case we found that the solubility of both dialkyl-diFIDT-di(N(CN)) OSCs was sufficient in chlorobenzene to fabricate transistor devices by blade-coating, a potentially scalable technique for solution based devices. 35,44 Devices were fabricated in a bottomcontact top-gate (BC -TG) configuration, with the active layer deposited onto the substrate at 100 1C, followed by spin coating of the gate dielectric (Cytop TM ) and thermal evaporation of the aluminium gate electrode. The key results are summarised in Table 2.…”