Proton-Induced Phase Transformations of Alkylated Diimine Platinum Complexes with Pyrazine Dithiolato

A series of platinum complexes, [Pt(pdt)(Rbpy)] (pdt = 2,3-pyrazine dithiolato; Rbpy = 4,4'-di-tert-butyl- (Ptpdt), 4,4'-dinonyl- (Ptpdt), and 4,4'-bis(3-octyltridecyl)-2,2'-bipyridyl (Ptpdt)), were synthesized and found to exhibit proton-responsive behavior in solution, crystalline, and liquid crystal (LC) states. All three complexes display distinct solvatochromic properties, ambipolar redox behavior, and reversible acid-base responsiveness. Upon treatment of Ptpdt with HCl in solution, monoprotonated species [Pt(Hpdt)(Rbpy)]·Cl (R = Bu, C9, and C8,10) are formed, wherein each Hpdt ligand features a C═S, a C-S, and a protonated nitrogen atom. Interestingly, similar monoprotonation is also induced in the condensed phases (crystalline phase for R = Bu and C9, or smectic LC phase for R = C8,10) upon exposure to HCl vapor, resulting in [PtHpdt]·Cl in the crystalline (R = Bu), low-crystalline (R = C9), and hexagonal columnar LC phases (R = C8,10). This work demonstrates a rare example of phase-dependent protonation behavior across molecular and supramolecular levels, offering a strategy for designing functional materials capable of dynamic phase modulation in response to acidic stimuli.