Vibrational spectroscopy is adopted to investigate the film structure of poly{[N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′bithiophene)} (P(NDI2OD-T2)) at the molecular level. Both Raman and IR spectra are measured for P(NDI2OD-T2) solutions and films. A good match with density functional theory (DFT) calculations at the B3LYP/6-311G** level is obtained, so that the main spectral features could be assigned. No significant spectral shifts are recorded when passing from very diluted solutions to the solid state, while clear variations in the relative intensity of specific spectral markers are observed. The comparison of the spectral patterns shown by IR spectra recorded with reflection−absorption IR spectroscopy (RAIRS) and in normal transmission experiments allows to derive a structural model of the polymer. In as-cast films, or in films subjected to mild thermal treatments, below the melting point, the backbone of the polymer chains lies preferentially in the substrate plane, with the T2 units lying flat parallel to the substrate and the NDI2OD unit featuring a dihedral angle θ with the T2 unit (θ ≈ 38°). This structure and polymer orientation is consistent with reported good bulk electron mobility in vertical diodes structures and high field-effect mobility in lateral fieldeffect transistors. Furthermore, we observe that upon a melt-annealing treatment, a clear modification of the RAIRS spectrum occurs suggesting either a loss of the preferential orientational order of the film or a flip of some domains featuring the polymer segments tilted out of the substrate.

Direct arylation (DA) is emerging as a highly promising method to construct inexpensive conjugated materials for large-area electronics from simple and environmentally benign building blocks. Here, we show that exclusive α-C–H selectivity is feasible in the DA of π-extended monomers having unsubstituted thiophene or furan units, leading to fully linear materials. Two new naphthalene diimide-based conjugated copolymers—P(FuNDIFuF₄) and P(ThNDIThF₄), composed of naphthalene diimide (NDI), furan (Fu) or thiophene (Th), and tetrafluorobenzene (F₄)—are synthesized. Insight into structure–function relationships is given by density functional theory (DFT) calculations and variety of experimental techniques, whereby the effect of the heteroatom on the optical, structural, and electronic properties is investigated. The use of furan (Fu) allows for enhanced solubilities, a smaller dihedral angle between NDI and Fu as a result of the smaller size of Fu, and a smaller π–π-stacking distance in the solid state. P(FuNDIFuF₄) also exhibits a more edge-on orientation compared to P(ThNDIThF₄). Despite these advantageous properties of P(FuNDIFuF₄), P(ThNDIThF₄) exhibits the highest electron mobility: ∼1.3 cm²/(V s), which is a factor of ∼3 greater than that of P(FuNDIFuF₄). The enhanced OFET performance of P(ThNDIThF₄) is explained by reduced orientational disorder and the formation of a terrace-like thin-film morphology

Combined systems of semiconducting polymers and aqueous electrolytes are emerging as a new frontier of organic electronics, with many promising applications in neuroscience, biomedicine, and photoelectrochemical cells. A detailed characterization of the effect of direct, prolonged contact with water in working conditions, typically upon visible light illumination, is thus urgently needed. Here, we report a comprehensive study of processes occurring in thin films of regioregular poly(3-hexylthiophene) (rr-P3HT), the election material for such applications, exposed to different environmental conditions. We demonstrate that the contact with saline solutions is not worse than contact with open air: in both situations the reversible formation of a charge transfer complex between polymer and molecular oxygen is the main phenomenon, enhanced by visible light illumination. Experimental data and theoretical modeling provide an insightful picture of the complex formation, as a precursor of photoactivated doping, and first unambiguously identify its spectral signature by means of vibrational spectroscopy techniques. In perspective, this work validates use of semiconducting polymers in contact with electrolytes and paves the way to new, rapidly emerging trends in organic electronics