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

Abstract

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.

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

“…28,31 Consequently, we attempted the preparation of the oxidized species of all three BBTTs. Analogously to dithieno [1,4]thiazine (DTT) 27,30,[38][39][40][41] chemical oxidation was carried out with antimony pentachloride as oxidant (Scheme 3). 41 By choice of solvent, temperature and equivalents of antimony pentachloride the oxidation stage can be reliably controlled.…”

“…Different steric hindrance unequivocally causes the absence of measurable luminescence in syn-syn BBTTs (bis [1]benzothieno[2,3-b:3′,2′-e] [1,4]thiazines), whereas inverse anellation of benzo [b]thiophene units leads to luminescence for syn-anti BBTTs (bis [1]benzothieno[2,3-b:2′,3′-e] [1,4] thiazines) peaking for anti-anti BBTTs (bis [1]benzo-thieno[3,2-b:2',3'e] [1,4]thiazines) with fluorescence quantum yields drastically increased to 45%. [26][27][28][29][30] Furthermore, anti-anti BBTTs represent the first known fused thiazines with antiaromatic character in the crystalline solid state. Likewise, being identified as Weitztype-redox systems, 31 BBTTs are outscoring their progenitors, i.e.…”

Synthesis and Electronic Properties of Conjugated syn,syn‐Dithienothiazine Donor‐Acceptor‐Donor Dumbbells

“…Thereby, the low optical band gaps of these redox switchable deep colored, emissive dumbbell systems can be consistently determined from both experimental and computational data. Upon transposing the synthetic strategy to (hetero)aryl bridged bis( anti , anti ‐dithieno[1,4]thiazine) dumbbell a cathodic shift of the oxidation potentials, and redshifted absorption and emission maxima with higher intensity can be expected [10,11] . Studies directed towards novel anti , anti ‐dithieno[1,4]thiazine substituted and bridged systems as novel donor‐acceptor‐donor and acceptor‐donor‐acceptor systems with low band gaps are currently underway.…”

“…As a novel type of fused 1,4‐thiazines we have recently introduced dithieno[1,4]thiazines, which can be considered as electron‐density enriched, tunable congeners of phenothiazines [10] . Most remarkably they not only outperform phenothiazine by lower oxidation potentials with higher radical cation stability, as novel types of donors for organic chromophores and electrophores [11] …”

Dithienothiazine Copolymers – Synthesis and Electronic Properties of Novel Redox-Active Fluorescent Polymers

“…Just very recently, we have introduced dithieno[1,4] thiazines, electron-density enriched congeners of phenothiazines, 14 which even have lower oxidation potentials with higher radical cation stability, as novel types of donors for organic chromophores and electrophores. 15 The paramount practical advantage of dithieno [1,4]thiazines over phenothiazines is their ready functionalization in the α,α'positions of the thieno cores. Based upon versatile transformations by lithiation-electrophilic trapping sequences, 16 halogenated and organometallic build blocks became accessible, which were employed to the efficient synthesis of dithienothiazine dimers, trimers and homopolymers.…”