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A series of novel phenothiazine based [1,2,4]triazolo[4, 3‐a]pyridine scaffolds were designed and synthesized in good yields by the oxidative cyclisation of phenothiazine pyridylhydrazones. Biological responses of all compounds toward a panel of human breast cancer cells (MDA‐MB‐231, MDA‐MB‐468, MCF7, SKBR3 and T47D) and human non‐tumorigenic epithelial breast cells (MCF10 A) were evaluated. Structure‐activity relationship revealed that compound with pendant phenyl ring on phenothiazine exhibited significant cytotoxic activity and apoptotic induction effects against breast cancer cell line with IC50 value 10.2 to 17.6 μM. Notably, the cytotoxic effect was 3.5 fold higher on cancer than non‐cancer cells, indicating potential control of breast cancer with lower side effects. Molecular docking studies confirmed the presence of hydrophobic contacts between appended phenyl ring, triazolopyridine and phenothiazine moieties with adjacent residues within the binding pocket of tubulin. One of the nitrogen in the triazolo ring also showed hydrogen bonding with tubulin. These tubulin interactions were also found with the taxane ring of paclitaxel. Cell cycle analysis confirmed the G2/M arrest induced by this compound on human breast cancer cells. Therefore, the potential anti‐cancer, pro‐apoptotic, and cell cycle arrest warrant further development of this molecule as a new class of anticancer agent.

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Smart materials displaying changes in colour and optical properties in response to acid stimuli are known as acidochromic materials. The recent progress and emerging trends in the field of smart organic materials with acidochromic properties reported in last seven years are presented herein. The molecular design of acidochromic organic materials, origin of the chromic and fluorochromic response to acid stimuli and related mechanisms are also discussed. Materials and systems covered in the review are divided according to the presence of basic moiety undergoing reversible protonation/ deprotonation, such as pyridine, quinoline, quinoxaline, azole, amine derivatives etc. in the molecules. Many donoracceptor molecules displaying acidochromic behaviour are cited. Alterations in visual colour change and optical properties supporting acidochromism are discussed for each example. Mechanistic studies based on the theoretical calculations, single crystal X-ray diffraction analysis and powder pattern diffraction analysis are also discussed. The application of these acidochromic molecules as acid-base switches, sensor films, self-erasable and rewritable media, data security inks, data encryption, molecular logic gates etc., are also reported. Thus, the review article aims at giving an insight into the design, characterization, mechanism and applications of organic acidochromic materials which will guide the researchers in designing and fine-tuning new acidochromic materials for desired applications

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