Bis[1]benzothieno[1,4]thiazines: Planarity, Enhanced Redox Activity and Luminescence by Thieno-Expansion of Phenothiazine

Dithienoazepine-Based Near-Infrared Dyes: Janus-Faced Effects of a Thiophene-Fused Structure on Antiaromatic Azepines

We here disclose that the incorporation of thiophene rings into a seven-membered 8π azepine in a fused fashion produces a useful antiaromatic core for near-infrared (NIR) dyes. In contrast to dibenzazepine derivatives with bent structures, dithieno-fused derivatives with electron-accepting groups adopt flat conformations in the ground state. The dithieno-fused derivatives exhibited broad absorption spectra that cover the visible region as well as sharp emission bands in the NIR region, which are considerably red-shifted relative to those of the dibenzo-fused congeners. Theoretical study revealed two contradictory effects of the less-aromatic thiophene-fused structure, i.e., the enhancement of the antiaromaticity of the adjacent azepine ring and the relief of the antiaromaticity through the contribution of a quinoidal resonance form. The combination of the dithienoazepine core with cationic electron-accepting groups produced a NIR fluorescent dye with an emission at 878 nm in solution.

3,9-Disubstituted Bis[1]benzothieno[3,2-b;2',3'-e][1,4]thiazines with Low Oxidation Potentials and Enhanced Emission

Dibrominated bis[1]benzothieno[3,2-b;2',3'-e][1,4]thiazines (BBTT) are efficiently synthesized and applied in Suzuki and Buchwald-Hartwig cross-coupling reactions to give access to 3,9-disubstituted BBTT derivatives with extended π-conjugation and enhanced electronic properties. For instance, 3,9-di(hetero)aryl substituted BBTT derivatives surpass their parent congeners phenothiazines with lower oxidation potentials and pronounced yellow to orange-red fluorescence (Φ_f ≈ 30-45%). In addition, 3,9-bis(di(hetero)arylamino substituted BBTT possess very high lying HOMO energy (E_HOMO = -4.46 to -4.83 eV), a favorable property of hole transport molecules. A representative X-ray structure analysis reveals that the central BBTT core in these extended π-systems is essentially planarized. Upon protonation of a 3,9-bis(di(hetero)arylamino) substituted BBTT, the absorption color shifts from yellow to deep blue with a concomitant loss of the emission. The optical properties of these novel BBTT derivatives can be plausibly rationalized by time-dependent density functional theory (TD(DFT)) calculations and correlation between experimentally determined oxidation potentials and σ_p parameters as well as between photophysical data and the specific substituent parameter σ_p^- by establishing electronic structure-property relationships.

Radical cations and dications of bis[1]benzothieno[1,4]thiazine isomers

Radical cations and dications of three isomeric bis[1]benzothieno[1,4]thiazines are (electro)chemically generated, spectroscopically characterized and assigned by (TD)DFT calculations.

Electron-Rich Phenothiazine Congeners and Beyond: Synthesis and Electronic Properties of Isomeric Dithieno[1,4]thiazines

A series of isomeric dithieno[1,4]thiazines is accessible through an intermolecular-intramolecular Buchwald-Hartwig amination starting from dihalodithienyl sulfides. The electronic properties of dithieno[1,4]thiazine isomers differ conspicuously over a broad range depending on the thiophene-thiazine anellation: a large cathodic (340 mV) or an anodic shift (130 mV) of the redox potentials relative to corresponding phenothiazines is possible. Structure-property relationships of the dithieno[1,4]thiazine constitution derived from DFT calculations and cyclic voltammetry not only reveal increased electron density but also different delocalization of the radical cations that determines the electrochemical properties significantly. In addition, photophysical properties (absorption and emission) qualify dithieno[1,4]thiazines as promising substitutes of phenothiazine and beyond due to increased tunable electron richness.

Dithieno[1,4]thiazines and Bis[1]benzothieno[1,4]thiazines-Organometallic Synthesis and Functionalization of Electron Density Enriched Congeners of Phenothiazine

This mini-review summarizes the syntheses and functionalizations of dithieno[1,4]thiazines and bis[1]benzothieno[1,4]thiazines, both electron density-enriched congeners of phenothiazines with remarkable electronic properties. Diversity-oriented, straightforward, and efficient syntheses, including versatile one-pot processes, have been developed for the anellated 1,4-thiazines as well as various functionalization for the expansion of the π-systems. Thereby, syntheses of different regioisomers depending on the (benzo)thieno-thiazine anellation are discussed, which exert a deep impact on the electronic properties. The tunable photophysical and electrochemical properties of dithieno[1,4]thiazines and bis[1]benzothieno[1,4]thiazines outscore phenothiazines on many points and promise an enormous potential in molecular electronics and applications beyond.

Diversity-oriented approach to functional thiophene dyes by Suzuki coupling-lithiation one-pot sequences

Functional thiophenes, e.g. for organic metal-free dye sensitized solar cells (DSSC), are accessible efficiently via a divergent and diversity-oriented synthetic strategy.

Game of Isomers: Bifurcation in the Catalytic Formation of Bis[1]benzothieno[1,4]thiazines with Conformation-Dependent Electronic Properties

Two regioisomers of bis[1]benzothieno[1,4]thiazine are unexpectedly obtained by tuning the catalytic conditions of the intermolecular-intramolecular Buchwald-Hartwig amination. Mechanistic insights and evidence of intermediates support a conclusive mechanistic rationale. Furthermore, a computationally based study on the influence of conformational aspects on the HOMO energy level of anellated 1,4-thiazine paves the way to enhance the electronic properties, thus successfully achieving higher luminescent and easier oxidizable syn- syn bis[1]benzothieno[1,4]thiazines.