Synthesis and Structural Analysis of Thiophene-Pyrrole-Based <i>S</i>,<i>N</i>‑Heteroacenes

Fused <i>S</i>,<i>N</i>-heterohexacene <b>4</b> was synthesized by applying Pd-catalyzed tandem Buchwald–Hartwig coupling and further functionalized to corresponding acceptor-capped derivatives <b>5</b> and <b>6</b> showing bond length equalization in the π-conjugated backbone and intense optical transitions. Organic thin film transistors (OTFTs) based on a vacuum-deposited film of <b>6</b> exhibit p-channel charge-carrier mobilities as high as 0.021 cm² V^–1 s^–1 and current on/off ratios of 10⁵

Exciton Coupling of Merocyanine Dyes from H- to J‑type in the Solid State by Crystal Engineering

A key issue for the application of π-conjugated organic molecules as thin film solid-state materials is the packing structure, which drastically affects optical and electronic properties due to intermolecular coupling. In this regard, merocyanine dyes usually pack in H-coupled antiparallel arrangements while structures with more interesting J-type coupling have been rarely reported. Here we show that for three highly dipolar merocyanine dyes, which exhibit the same π-scaffold and accordingly equal properties as monomers in solution, the solid-state packing can be changed by a simple variation of aliphatic substituents to afford narrow and intense absorption bands with huge hypsochromic (H) or bathochromic (J) shifts for their thin films and nanocrystals. Time-dependent density functional theory calculations show that the energetic offset of almost 1 eV magnitude results from distinct packing motifs within the crystal structures that comply with the archetype H- or J-aggregate structures as described by Kasha’s exciton theory

Influence of Solid-State Packing of Dipolar Merocyanine Dyes on Transistor and Solar Cell Performances

A series of nine dipolar merocyanine dyes has been studied as organic semiconductors in transistors and solar cells. These dyes exhibited single-crystal packing motifs with different dimensional ordering, which can be correlated to the performance of the studied devices. Hereby, the long-range ordering of the dyes in staircase-like slipped stacks with <i>J</i>-type excitonic coupling favors charge transport and improves solar cell performance. The different morphologies of transistor thin films and solar cell active layers were investigated by UV–vis, AFM, and XRD experiments. Selenium-containing donor–acceptor (D–A) dimethine dye <b>4</b> showed the highest hole mobility of 0.08 cm² V^–1 s^–1. BHJ solar cells based on dye <b>4</b> were optimized by taking advantage of the high crystallinity of the donor material and afforded a PCE of up to 6.2%