π-Extended Thiadiazoles Fused with Thienopyrrole or Indole Moieties: Synthesis, Structures, and Properties

Abstract

We report the syntheses, structures, photophysical properties, and redox characteristics of donor-acceptor-fused π-systems, namely π-extended thiadiazoles 1-5 fused with thienopyrrole or indole moieties. They were synthesized by the Stille coupling reactions followed by the PPh(3)-mediated reductive cyclizations as key steps. X-Ray crystallographic studies showed that isomeric 1b and 2b form significantly different packing from each other, and 1a and 4a afford supramolecular networks via multiple hydrogen bonding with water molecules. Thienopyrrole-fused compounds 1b and 2b displayed bathochromically shifted intramolecular charge-transfer (CT) bands and low oxidation potentials as compared to indole-fused analog 3b and showed moderate to good fluorescence quantum yields (Φ(f)) up to 0.73. In 3b-5b, the introduction of electron-donating substituents in the indole moieties substantially shifts the intramolecular CT absorption maxima bathochromically and leads to the elevation of the HOMO levels. The Φ(f) values of 3-5 (0.04-0.50) were found to be significantly dependent on the substituents in the indole moieties. The OFET properties with 1b and 2b as an active layer were also disclosed.

A Series of π‐Extended Thiadiazoles Fused with Electron‐Donating Heteroaromatic Moieties: Synthesis, Properties, and Polymorphic Crystals

“…The absorption and fluorescence spectra of 4 – 8 were recorded in various solvents to investigate their photophysical properties in detail, and the relevant data for discussion are summarized in Table 1. We recently found that the longest absorption maxima (${\lambda {{{\rm abs}\hfill \atop {\rm max}\hfill}}}$ ) and the fluorescence maxima (${\lambda {{{\rm fl}\hfill \atop {\rm max}\hfill}}}$ ) are increasingly redshifted from 3 to 2 to 1 , and not only the nature of the aromatic rings fused with the pyrrole rings, but also their orientation affect the photophysical properties 10. Therefore the photophysical data for 4 – 8 are chiefly discussed from the viewpoint of the effects of 1) the extension of multifused π‐frameworks compared with 1 – 3 , that is, benzannulation, 2) the nature of the aromatic rings annulated to the pyrrole rings, that is, benzothiophene, naphthalene, and benzofuran, and 3) their orientation.…”

“…The Φ f values in CH 2 Cl 2 for most compounds seem to be lower than those in other solvents, although the reason for this is unclear at present. We recently demonstrated that the moieties annulated to the pyrrole rings significantly affect the fluorescence efficiency 10. Compounds 1 and 2 display moderate‐to‐high Φ f values of 0.33–0.73 and 0.34–0.51, respectively, whereas 3 displays significantly low Φ f values of 0.04–0.07.…”

“…On the other hand, we envisioned that the fusion of electron‐donating and ‐accepting heteroaromatics in ring‐fused polycyclic skeletons leads not only to the intramolecular CT interactions characteristic of D–A‐substituted compounds but also to efficient intermolecular π–π stacking interactions in the solid state. On this basis we recently designed and synthesized six‐ring fused thiadiazoles 1 – 3 10 in which highly electron‐ donating thienopyrrole or indole moieties are annulated to an electron‐accepting benzothiadiazole (BTD) unit to form a new class of D–A‐fused chromophores 11–16. We demonstrated that thiadiazoles 1 – 3 display fluorescence solvatochromism and electrochemical amphoterism as well as forming dense π‐stacking structures.…”

Heteroatom-Bridged Benzothiazolyls for Organic Solar Cells: A Theoretical Study

“…The nitrogen bridges not only planarize the molecular structure to induce stronger intermolecular π-π interaction but also play 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 an important role in determining the electronic and photophysical properties of the resulted polymers for OPV applications. The relatively low PCE of the N-bridged DTBT is mainly due to the high-lying HOMO and LUMO resulted from the strong electron donating ability of N atom 27 .…”

Theoretical study on the electronic structures and properties of diindolocarbazole isomers

“…Meanwhile, intermolecular frontier orbital overlap in molecular organizations is essential to enhance charge carrier mobility. The multifused aromatic and heteroaromatic compounds, for instance, are promising candidates on account of their flat and rigid frameworks, which provide the effective extension of π‐conjugation and allow for forming a dense molecular packing . Thus, they are expected to obtain spectacular properties such as strong fluorescence and high carrier mobility.…”