A design strategy towards stable fluorenyl radicals (FRs) is established by introducing donor-π-radical (D-π-R) conjugation between amine N atoms and FR centers through phenyl or 9-anthryl moieties. Four FRs with or without N atom containing protecting groups were designed and synthesized for comparison. X-ray crystallographic analysis displayed planar fluorenyl skeletons of CDP-FR and MA-FR, which form large dihedral angles with protecting groups. Even though, the increased bond-order of C-C and C-N bond be-tween radical center and N atoms by Wiberg bond analysis of all FRs confirmed the D-π-R conjugation. Time-dependent DFT calcula-tions based on frontier molecular orbital analysis further revealed the contribution of D-π-R structures as donor-acceptor effect on the lowest energy absorptions of carbazole and diphenylamine substituted CDP-FR and DPAA-FR. Therefore, beneficial from D-π-R conjugations, CDP-FR and DPAA-FR showed better photo-stability than TP-FR and MA-FR. Our study here provides a new strategy to design and synthesize persistent stable monoradicals.