| Recently,metal-free organic room temperature phosphorescence（RTP）has attracted intense attention in diverse applications such as anti-counterfeiting,molecular sensing and displays due to their long-lived emission life-times.Until now,most luminescent materials with phosphorescence are confined to inorganic and precious metal complexes with distinct shortcomings such as high cost,biological toxicity,and instability in aqueous solutions.Therefore,developing a novel type of pure organic phosphorescent material is very meaningful.However,the development of efficient and ultralong organic phosphorescence（UOP）still remains a great challenge.The key issues involve the inefficient intersystem crossing（ISC）caused by weak spin–orbit coupling（SOC）and the rapid non-radiative decay due to molecular motions and oxygen quenching,among other things.Inspired by the widespread d-pπbond in transition metal complexes,we proposed a d-pπbond strategy for regulate excited-state electronic configuration to prolong phosphorescence lifetime（up to 19 times）.（1）Organic compounds containing phenothiazine（unique non-planar butterfly structure）units were chosen as model systems.Through subtle chemical modification,that is,a one-step sulfur oxidation,a d-pπbond was introduced into the luminogens.Luminogens of DOPPMO and DOPEO were obtained in overall yields of 77%and86%,respectively.The phase purity and molecular packing were confirmed by powder XRD and single-crystal analysis.（2）After obtaining a single crystal,a series of characterizations were carried out on the photophysical properties of the four compounds.After the introduction of the d-pπbond,the lifetime was hugely improved（from 24 ms to 455 ms,19 times）.（3）Furthermore,crystal analysis and theoretical calculations reveal that d-pπbonds play a significant role in manipulating the electronic configuration and molecular stacking of these compounds.A nearly pure（p（11）p*）configuration of T1 and a more rigid molecular environment in the crystal state were attained,which gave rise to a substantial increase of the phosphorescence lifetime.（4）Given the remarkably different afterglow-time features,a primary application for data encryption was demonstrated.This work provides a new idea for constructing new ultralong phosphorescent materials and prolonging room temperature phosphorescence lifetime from the perspective of chemical bonds. |
