Mono‐Heteroatom Harnessing Excited‐state Structural Planarization for Dihydrodibenzo[a,c] phenazines

: With the aim of generalizing the structure-properties relationship of bending heterocyclic molecules that undergo prominent photoinduced structural planarization (PISP), a series of new dihydrodibenzo[ac]phenazine derivatives in which one nitrogen atom is replaced by oxygen (PNO), sulfur (PNS), selenium (PNSe), or dimethylmethanediyl (PNC) was strategically designed and synthesized. Compounds PNO, PNS, and PNSe have significantly nonplanar geometries in the ground state, which undergo PISP to give a planarlike conformer and hence a large emission Stokes shift. A combination of femtosecond early relaxation dynamics and computational approaches established an R*→I* (intermediate)→P* sequential kinetic pattern for PNS and PNSe, whereas PNO undergoes R*→P* one-step kinetics. The polarization ability of the substituted heteroatoms, which is in the order O

Keywords:

• Chemistry
• Chemical-mechanical planarization
• Excited state
• Heteroatom
• Photochemistry
• Organic chemistry
• Lone pair
• Conformational isomerism
• Crystallography
• Delocalized electron
• Substituent
• Inorganic chemistry
• Ground state
• Stokes shift

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