An efficientsynthesis of novel type of dipyrido-1,4-thiazine (4) was elaborated in the reactions of two pairs of 3,4-disubstituted pyridines in DMF. The reactions proceeded through the S→N type of the Smiles rearrangement of the resulting 4,4'-dipyridinyl sulfide. In the case of formation of 10-(3'-nitro-4'- pyridinyl)-2,7-diazaphenothiazine (5) double rearrangement was observed. 10H- 2,7-diazaphenothiazine
We present a fully reversible and highly efficient on-off photoswitching of magnetic resonance imaging (MRI) contrast with green (500 nit), and violet-blue (435 nm) light. The contrast change is based on inframolecular light-driven coordination-induced spin state switch (LD-CISSS), performed with azopyridine-substituted Ni-porphyrins. The relaxation time Of the solvent protons in 3 mM solutions of the azoporphyrins in DMSO was switched between 3.5 and 1.7 s. The relaxivity of the contrast agent changes by a factor of 6.7. No fatigue or side reaction was observed, even after >100 000 switching cycles in air at room temperature. Electron-donating substituents at the pyridine improve the LD-CISSS in two ways: better photostationary states are achieved, and intramolecular binding is enhanced.
Rasala, D., Bulletin de la Societe Chimique de France, 1992, # 1, p. 79 - 84