“…Phenol blue (PB), also known as N , N -dimethylindoaniline, N -(4-dimethylaminophenyl)-1,4-benzoquinoneimine, is a well-known nonfluorescent solvatochromic dye − which has been widely studied by spectroscopic methods, such as resonance Raman scattering, − time-resolved transient absorption (TRTA), , and NMR, , as well as theoretical simulations. − PB is composed of an electron-donating (dimethylaniline) moiety connected to an accepting (benzoquinone monoimine) one by a π-conjugated bridge. Upon photoexcitation, charge transfer (CT) occurs from the donor to the acceptor moiety, and the contribution from the zwitterionic resonance structure becomes stronger than that from the covalent quinoneimine one in the first excited-singlet (S 1 ) state (Chart , top).…”