Polymorphism and Mechanochromism in 2-Phenylbenzothiazole Cyclometalated Pt Complexes with Chelating NO Ligands.

New cyclometalated Pt complexes with 2-phenylbenzothiazole (pbt) and two different picolinate ligands [Pt(pbt)(R-pic-κ)] (R = H (), OH ()) were prepared. In contrast to , the OH substituent group on allows modulation of the packing in the solid state through donor-acceptor H-bonding interactions with the CHCl solvent. Thus, three pseudopolymorphs of with different aggregation degrees were isolated, including yellow , orange-red () and black () with emissions at 540, 656, and 740 nm, respectively, in the solid state at 298 K. and can be transformed to the pristine solid . Studies of their crystal structures show that and stack in columns with only π···π stacking interactions, whereas displays strong aggregated 1D infinite chains based on Pt···Pt and π···π stacking interactions, consistent with the colors and the photophysical properties, measured in several media. Interestingly, and exhibit reversible mechanochromic behavior with high contrast in the color and color emission upon mechanical grinding due to a phase transition between a crystalline and an amorphous state, as confirmed by powder X-ray diffraction (PXRD) studies. Theoretical calculations indicate that Pt···Pt contacts are more relevant in the trimers and tetramers than in the dimers, particularly in their T states, associated with a change from a IL/MLCT transition in the monomer to MM(L+L')CT in the oligomers. Noncovalent interaction (NCI) theoretical studies indicate that the π···π stacking among chelates also exerts a strong influence in the metal-metal-to-ligand charge transfer transition character.