Synthesis, Molecular Packing, and Electrical Properties of New Regioisomeric n-type Semiconducting Molecules with Modification of Alkyl Substituents Position

Abstract

We design and synthesize a series of regioisomeric n-type small molecules, which have an identical diketopyrrolopyrrole (DPP) core and 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)­propanedinitrile (INCN) terminal groups with octyl substituents at different positions. The isomeric structures are confirmed by two-dimensional NMR spectroscopy based on the heteronuclear multiple-bond coupling method. Incorporation of the electron-deficient DPP and strongly electron-withdrawing INCN groups yields deep frontier molecular orbitals with n-type charge-transport properties in solution-processed organic field-effect transistors (OFETs). Interestingly, a minor change in the substitution position of the octyl side chains significantly influences the optoelectronic and morphological properties of the thin film. The polycrystalline morphology of the as-cast films is reorganized differently with thermal annealing depending on the octyl topology, significantly affecting the OFET performance. With thermal treatment at 200 °C, the kinked DPP­(EH)-INCNO1 (EH = 2-ethylhexyl) structures transform into single crystalline-like structures, exhibiting a remarkably improved electron mobility up to ∼0.6 cm2V−1 s−1 compared with DPP­(EH)-INCNO2 isomers. The more linear DPP­(EH or HD)-INCNO2 (HD = 2-hexyldecyl) molecules become more crystalline with thermal treatments, but their polycrystalline packing structures with large grain boundaries are the main reason for their lower electron mobility. When the solubilizing alkyl substituents are selected, careful molecular design is needed, with consideration of both the solubility and intermolecular packing, for optimizing the optoelectronic properties.

Enlightening the Well-Controlled Photochemical Behavior of 1,1-Dicyanomethylene-3-Indanone-Functionalized π-Conjugated Molecules

“…16 Common molecular-level approaches to optimizing OPV thin film morphology and charge transport 17−19 include modifying the π-conjugated backbone structure and/or planarity and the structure and/or placement of solubilizing side chains. 20−24 Modifications specific to INCN-containing molecules include altering the solubilizing alkyl chain placement along the π-conjugated backbone 25 or on the indanone ring 26 and introduction of halogen atoms 27 or methoxy groups 28 structural changes, while sometimes seemingly minor, can induce a higher film absorption coefficient, larger crystalline coherence, and higher electron mobility, ultimately leading to higher PCE. We recently reported the ability of dicyanorhodanine (RCN) functionalized thiophenes to undergo Z/E configurational isomerization upon photoirradiation 29 and observed that the solid-state morphologies and optoelectronic properties of thin films from RCN-containing oligomers can be significantly affected by configurational composition.…”

Dielectric behavior of curcuminoid polymorphs on different substrates by direct soft vacuum deposition

“…As mentioned earlier, molecular packing, crystal structure, and the interplay between molecular structure and substrate surfaces have an important impact on the electrical properties of materials. 49 , 50 , 51 , 52 To gain insight into the correlation between the AlkCCMoid structure with its electrical properties we used 1-SC, 1-MP, and 1-SUB (onto Si/SiO 2 surfaces) to perform XRD, GIWAXS, and electrical measurements.…”

Chalcogenopheno[3,2-b]pyrrole-Containing Donor–Acceptor–Donor Organic Semiconducting Small Molecules for Organic Field-Effect Transistors

“…A thiophene spacer and DPP were chosen in this work because of a better reported performance in DPP- and TP-based small molecules . To study the difference between chalcogenopheno­[3,2 -b ]­pyrroles and thieno­[3,2- b ]­thiophene (TT), a 2-ethylhexyl side chain on DPP and methyl side chain on chalcogenopheno­[3,2- b ]­pyrroles was utilized to maintain sufficient solubility of the final molecules and retain the similarity of the donors. − The pyrrole located at the end of the molecules minimizes the dihedral angle that may be generated by the pyrrole side chain. By studying these four molecules, we have, for the first time, investigated all reported chalcogenopheno­[3,2- b ]­pyrroles in the same system and compared them to thieno­[3,2- b ]­thiophene, thus obtaining insights into the differences between chalcogenopheno­[3,2 -b ]­pyrroles and TT at the molecular level.…”