Measurement of Solvation Ability of Solvents by Porphyrin-Based Solvation/Desolvation Indicators

A new solvent scale, solvation ability (SA), was developed to arrange solvents in the order of their SA for large pi-conjugated compounds. The SA of a solvent was determined in a binary solvent system of an assessed solvent and a standard "good" solvent (GS) or "poor" solvent (PS), chloroform or methylcyclohexane, respectively, in the presence of two types of solvation/desolvation indicators, 1Zn(2) and 2Zn(2). The latter comprises bis(imidazolylporphyrinatozinc) linked via a 1,3-butadiynylene moiety having linear alkyl and hydrophilic side chains, respectively. GSs and PSs give extended (E-) and stacked (S-) supramolecular polymers of the indicators, respectively. SA values are defined as vol % of the standard solvent added to an assessed solvent to give the balance point where comparable amounts of E- and S-polymers of the indicators coexist. GSs and PSs have positive and negative signs, respectively. In this study, the SA of 25 solvents was determined. The SA values with indicator 1Zn(2) were as follows: ethyl acetate (-81), hexane (-50), cyclohexane (-47), CCl4 (-25), chloroform (50), and nitrobenzene (79).