Fig. 2
Absorption and fluorescence spectra of 1. a In CH2Cl2. b In CH3OH. c Absorption spectral changes versus pHm in CH3OH. d The absorption changes at 618 nm during the pHm titration. e Fluorescence spectral changes versus pHm in CH3OH. f Fluorescence changes at 635 nm during the pHm titration. The concentration of 1 was 10−5 M for absorption and 10-6 M for fluorescence measurements. Definition of pHm: pHm, the apparent pH in methanol, is determined in analogy to pHe, a measure of the acid strength of ethanol and high ethanol content fuels as measured directly with a common pH electrode in high-content alcoholic solution, see ASTM D6423–08, ASTM International, West Conshohocken, PA (U.S.).
