Thermochromism of Corrole Solutions in Ethanol

The temperature dependence of electronic absorption spectra of a family of 5,10,15-triarylcorroles in EtOH solution was studied in the range 288–328 K. Corroles in EtOH existed as mixtures of the free base and deprotonated form, the ratio of which was determined by the donor–acceptor properties of the peripheral substituents. Free corrole bases deprotonated as the temperature rose. Deprotonation obeyed the van′t-Hoff equation with activation energy E a = 2.0 kcal/mol, which was the same within measurement error limits for all studied compounds. The temperature was proposed to affect indirectly the deprotonation by changing the EtOH dielectric constant. The decreasing dielectric constant with increasing temperature shifted the acid–base equilibrium toward formation of the deprotonated form.