Absorption, Fluorescence, and Two‐Photon Excitation Ability of 5‐o‐Tolyl‐11 (or 13)‐o‐tolylisoindolo[2,1‐a]quinolines Prepared by Ring‐Closing Metathesis and [2+3] Cycloaddition

We have successfully improved the fluorescence quantum yield of isoindolo[2,1‐a]quinoline derivatives by suppressing the rotation of the phenyl groups at positions 5 and 11 (or 13). Additionally, we found that the planarity of these phenyl groups at positions 5 and 11 (or 13) of isoindolo[2,1‐a]quinoline derivatives is crucial for two‐photon absorption properties. The fluorescent properties was improved by introducing ortho‐substituents to the phenyl groups at the 5‐ and 11 (or 13) ‐positions of isoindolo[2,1‐a]quinoline, thereby increasing the dihedral angle and rotational energy. The planarity of these phenyl groups at positions 5 and 11 (or 13) of isoindolo[2,1‐a]quinoline derivatives is crucial for two‐photon absorption properties.