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

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.

Recent Advances in Monocomponent Visible Light Photoinitiating Systems Based on Sulfonium Salts

During the last decades, multicomponent photoinitiating systems have been the focus of intense research efforts, especially for the design of visible light photoinitiating systems. Although highly reactive three-component and even four-component photoinitiating systems have been designed, the complexity to elaborate such mixtures has incited researchers to design monocomponent Type II photoinitiators. Using this approach, the photosensitizer and the radical/cation generator can be combined within a unique molecule, greatly simplifying the elaboration of the photocurable resins. In this field, sulfonium salts are remarkable photoinitiators but these structures lack absorption in the visible range. Over the years, various structural modifications have been carried out in order to redshift their absorptions in the visible region. In this work, an overview of the different sulfonium salts activable under visible light and reported to date is proposed.

Efficient Construction of Symmetrical Diaryl Sulfides via a Supported Pd Nanocatalyst-Catalyzed C-S Coupling Reaction

Aryl sulfides play an important role in pharmaceuticals, biologically active molecules and polymeric materials. Herein, a general and efficient protocol for Pd@COF-TB (a kind of Pd nanocatalyst supported by a covalent organic framework)/DIPEA-catalyzed one-pot synthesis of symmetrical diaryl sulfides through a C-S coupling reaction from aryl iodides and Na₂S₂O₃ is developed. More importantly, the addition of N,N-diisopropylethylamine (DIPEA) can not only enhance the catalytic activity of a Pd@COF-TB nanocatalyst, but also effectively inhibit the formation of biphenyl byproducts, which are a product of Ullmann reaction. Besides, it has been confirmed that the aryl Bunte salts generated in situ from Na₂S₂O₃ and aryl iodides are the sulfur sources involved in this C-S coupling reaction. With the strategy proposed in this work, a variety of symmetrical diaryl sulfides could be obtained in moderate to excellent yields with a high tolerance of various functional groups. Moreover, a possible mechanism of this Pd nanoparticle-catalyzed C-S coupling reaction is proposed based on the results of controlling experiments.

Phenothiazine-Based Luminophores with AIE, Solvatochromism, and Mechanochromic Characteristics

Aggregation-induced emission (AIE) fluorescent molecules with unique photoelectric properties have received extensive attention due to the wide range of applications. In this work, two novel phenothiazine-based luminophores DPE-PTZ-Cl and DPE-PTZ-CF₃ were designed based on the frontier molecular orbital (FMO) theory and construction strategy of AIEgens. As expected, both of the luminophores displayed typical AIE behavior and realized the spatial separation of FMOs, which was confirmed by the positive solvatochromism behavior. Their AIE properties could be attributed to the twisted three-dimensional (3D) conformation. Such a conformation resulted from "butterfly-like" phenothiazine and a multirotor structure of diphenylethylene. The spatial separation of FMOs originated from the push-pull electronic synergistic effect of the donor-acceptor (D-A) architecture. Interestingly, DPE-PTZ-Cl also showed a rare blue-shifted mechanochromic (MC) luminescence property. Single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD) experiments were carried out to reveal that the phase transformation between crystalline and amorphous states was responsible for the peculiar solid-state luminescence phenomenon.

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.

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.