Synthesis of Doubly Fused Phenothiazine-Embedded Dithiasapphyrins

The condensation of phenothiazine-based tripyrrane with bithiophene diol in the presence of acid catalysts resulted in the formation of unique doubly fused phenothiazine-embedded dithiasapphyrins instead of the expected nonfused phenothiazine-embedded dithiasapphyrins. Four examples of different meso-substituted N-C-fused dithiasapphyrins were synthesized to demonstrate the versatility of the (3 + 2) condensation reaction. High-resolution mass spectrometry and different spectroscopic and computational techniques were used to confirm the intramolecular ring fusion in our reported macrocycles. DFT studies showed that the double N-C-fused dithiasapphyrins were thermodynamically more stable as opposed to the nonfused phenothiazine-embedded dithiasapphyrin. The nonaromaticity in the macrocycles was established with the help of NMR, absorption, and DFT studies. The absorption spectra showed distinct bands in the visible region which were bathochromically shifted to the NIR region after protonation. The electrochemical studies revealed the highly electron-rich nature of the macrocycles, and theoretical studies were similar to the experimental observations.