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 π-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 (S₁) excited-state minimum disappear and significantly lowers the S₁ excited-state potential energy surface (PES), leading to barrierless τ-torsion and φ-torsion excited-state relaxation and eliciting the φ-torsion S₁ excited-state minimum. This finding is critical since a strong π-donating group like p-NMe₂ may do the same things to other fluorophores.