Phenothiazine Based Mechano-fluorochromic Gels and Solids: Superhydrophobic Surface Formation and Crystal-to-Crystal Phase Transition

Organic materials exhibiting mechano-fluorochromic behavior in their gel state are extremely rare in the literature. Similarly, examples of mechano-fluorochromic organic materials with crystal-to-crystal phase transitions have not been reported till date. Herein, we achieved these two remarkable properties in phenothiazine derivatives S1 and S2 [(E)-N'-((10-ethyl-10H-phenothiazin-3-yl)methylene)-3,4,5-tris(hexadecyloxy)benzohydrazide and (E)-N'-((10-ethyl-10H-phenothiazin-3-yl)methylene)isonicotinohydrazide)], where S1 formed mechano-luminescent xerogel and S2 exhibited the rare feature of crystal-to-crystal phase transition with mechano-luminescence behavior. Study of the photo physical properties of S1 and S2 indicated the suppression of twisted intramolecular charge transfer (TICT) upon self-assembly, leading to blue shifted emission from S1 and S2. While both S1 and S2 exhibited the propensity to aggregate and disclosed the aggregation induced emission (AIE) behavior in a binary solvent (THF/H2O) mixt...