Dramatic changes in the excited-state behaviour of the green fluorescent protein chromophore by a strong π-donating group through significantly lowering the excited-state potential energy surface with photoinduced intramolecular charge transfer

A strong pi-donating group like p-NMe2 dramatically changes the excited-state behavior of the green fluorescent protein (GFP) chromophore, such as realizing charge-transfer absorption and executing significant photoinduced intramolecular charge transfer (ICT), which makes a planar first singlet (S-1) excited-state minimum disappear and significantly lowers the S-1 excited-state potential energy surface (PES), leading to barrierless tau-torsion and phi-torsion excited-state relaxation and eliciting the phi-torsion S-1 excited-state minimum. This finding is critical since a strong pi-donating group like p-NMe2 may do the same things to other fluorophores.