Four Ounces Can Move a Thousand Pounds: A Nitrogen Atom Greatly Influences Phosphorescence and Photochromism

Abstract How to precisely regulate ultralong phosphorescence and photochromism in a single molecule is a current technical challenge that needs to be solved. Herein, a simple atom‐level modification method is developed to tune both ultralong phosphorescence and photochromism of organic molecules. A series of nitrogen‐modified dinaphthylamine‐structured molecules is designed and synthesized by altering the number and position of the N atom. All these molecules demonstrate colorful ultralong phosphorescence and tunable photochromism due to the subtle structural change. The changing position of the N atom greatly influences the T1 energy level, intersystem crossing (ISC) efficiency, Singlet‐Triplet Energy Gap (ΔEST), and the electron density (Mulliken charge) of the ‐NH‐ group. The lone electron pair of ‐NH‐ will shift to the nitrogen‐modified aromatic ring due to its strengthened electron‐drawing ability. Photo‐induced generation of cation radicals is involved in the photochromic process, and these molecules show a controllable recovery rate due to the different electron density of the ‐NH‐ group. In this case, phosphorescence and photochromism are two competitive pathways for excitons. This work realizes the effect of minor modifications from the atomic level to tune the UORTP properties, as well as photochromism to a large extent.