Abstract
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.
Highlights
Phenothiazines have become attractive in numerous applications in organic electronics due to their outstanding electronic properties: fully reversible one-electron oxidations at low potentials,[1] rather unusual among organic compounds on the one hand, and luminescence, rather unusual in combination with redox activity on the other hand
Just recently we established a fast and efficient multicomponent access to diversely acceptor-substituted thiophenes based on lithiation-electrophile trapping sequences,[12] we set out for one-pot pseudo five-component syntheses of 2,6-diacceptor-substituted dithieno[1,4]-thiazines (Scheme 2)
The acceptor substituted phenothiazine 6 was synthesized in a one-pot fashion for electronic comparison
Summary
We present efficient one-pot syntheses of six novel 2,6-disubstituted syn–syn and anti–anti dithieno[1,4]thiazines 3 as well as a comparative study on their ground and excited state electronic properties and electronic structures. In a similar fashion 3,7-dibromo-10-phenyl-10H-phenothiazine (5),[13] by brominelithium exchange, was reacted in the LiForK sequence to give the phenothiazine derivative 6. This type of donor-acceptor conjugate can be often found in efficient bulk-heterojunction (BHJ) solar cells.[14]
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