Antifreezing Effect of the Central Metal on Porphyrin Supercooled Liquid and Glass

Abstract

The profound impact of the central metal on the morphological properties of metalloporphyrins bearing 3,4,5-tri((S)-dihydrocitronellyloxy)phenyl groups at the diagonal meso-positions is disclosed. Systematic comparison of the free-base porphyrin 1H 2 with metalloporphyrins 1Ms incorporating Ni(II), Cu(II), and Zn(II) as the central metal found the counterintuitive antifreezing effect of the central metal; 1H 2 crystallizes immediately after the removal of the solvent, while the central metal retards nucleation. We interpret that the miscibility of the elastic alkyl chains and the porphyrin segment is crucial in imparting fluidity to 1M and smooth nucleation in the context of classical nucleation theory, while the full rationalization of the thermal behaviors requires the existence of the nuclei precursor according to the two-step nucleation model. The morphological behaviors of 1Ms are highly susceptible to only marginal differences in the chemical structure, presumably due to the relatively large discrete size of the porphyrin ring, approximately 1 nm. The somewhat counterintuitive antifreezing effect of the central metal is interpreted to arise from the increased viscosity due to the enhanced molecular interactions.

Metallic Lustrous Porphyrin Foil with an Exceptional Refractive Index

“…The solution-phase experiments of polymers were severely limited by the colloidal metastable nature. It should be noted that the solubility of polymers 1 and 2 (Scheme ) gradually dropped during storing as porphyrin foil and even as solutions, which became insoluble in organic solvents, such as chloroform, toluene, and THF, presumably due to physical cross-linking of the polymer backbones by decreasing the free volume via π-stacking, based on our recent findings for the glassy porphyrin unit . Based on the following experimental observations, we consider that the polymers irreversibly precipitate or colloidally aggregates depending on thermal desolvation, i.e.…”

“…It should be noted that the solubility of polymers 1 and 2 (Scheme 1) gradually dropped during storing as porphyrin foil and even as solutions, which became insoluble in organic solvents, such as chloroform, toluene, and THF, presumably due to physical crosslinking of the polymer backbones by decreasing the free volume via πstacking, based on our recent findings for the glassy porphyrin unit. 35 Based on the following experimental observations, we consider that the polymers irreversibly precipitate or colloidally aggregates depending on thermal desolvation, i.e., lower critical solution temperature-like behaviors. 36 The proportion of the Soret band at 499 nm became smaller than the proportion at 462 nm after heating at 343 K (Figure S1A), suggesting the precipitation of highly stacked components.…”