Communication of Bichromophore Emission upon Aggregation - Aroyl-S,N-ketene Acetals as Multifunctional Sensor Merocyanines.

Aroyl-S,N-ketene acetal-based bichromophores can be readily synthesized in a consecutive three-component synthesis in good to excellent yields by condensation of aroyl chlorides and an N-(p-bromobenzyl) 2-methyl benzothiazolium salt followed by a Suzuki coupling, yielding a library of 31 bichromophoric fluorophores with substitution pattern-tunable emission properties. Varying both chromophores enables different communication pathways between the chromophores, exploiting aggregation-induced emission (AIE) and energy transfer (ET) properties, and thus, furnishing aggregation-based fluorescence switches. Possible applications range from fluorometric analysis of alcoholic beverages to pH sensors.

Widely Electronically Tunable 2,6-Disubstituted Dithieno[1,4]thiazines-Electron-Rich Fluorophores Up to Intense NIR Emission.

2,6-Difunctionalized dithieno[1,4]thiazines were efficiently synthesized by (pseudo)five- or (pseudo)three-component one-pot processes based on lithiation-electrophilic trapping sequences. As supported by structure-property relationships, the thiophene anellation mode predominantly controls the photophysical and electrochemical properties and the electronic structures (as obtained by DFT calculations). From molecular geometries and redox potentials to fluorescence quantum yields in solution, the interaction of the dithieno[1,4]thiazine-core with the substituents causes striking differences within the series of regioisomers. Most interestingly, strong acceptors introduced in anti-anti dithieno[1,4]thiazines nearly induce a planarization of the ground-state geometry and a highly intense NIR fluorescence (ΦF =0.52), whereas an equally substituted syn-syn dithieno[1,4]thiazine exhibits a much stronger folded molecular structure and fluoresces poorly (ΦF =0.01). In essence, electrochemical and photophysical properties of dithieno[1,4]thiazines can be tuned widely and outscore the compared phenothiazine with cathodically shifted oxidation potentials and redshifted and more intense absorption bands.

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.