摘要
A series of green fluorescent protein chromophore analogues incorporating nitrogen-donor units-carbazole (Cz), phenothiazine (PTZ), phenoxazine (PXZ), and acridine (ACR)-was synthesized to elucidate the impact of donor strength and substitution topology on excited-state dynamics. The para-substituted derivatives display strong intramolecular charge-transfer (ICT) absorption and efficient emission, whereas the meta-substituted analogues exhibit weaker ground-state conjugation but significantly larger Stokes shifts and enhanced charge separation. Among the donors, PXZ and PTZ are particularly effective due to their distorted heterocyclic geometries, which facilitate HOMO-LUMO decoupling. The exceptionally large Stokes shifts observed in PTZ derivatives are attributed to extensive excited-state relaxation involving quasi-equatorial to quasi-axial (eq -> ax) conformer interconversion, a mechanism confirmed by the emergence of blue-shifted, structured emission at 77 K. Additionally, p-Cz exhibits enhanced fluorescence in polar solvents driven by the amino conjugation effect, while p-ACR demonstrates reversible mechanofluorochromism. These findings provide a comprehensive framework for designing organic luminophores with tunable ICT emission and intrinsic large Stokes shifts for advanced photonic and sensing applications.