Precisely Regulating 2.45 s Pure Blue Room‐Temperature Phosphorescence via Supramolecular Coordination

Achieving tunable blue room‐temperature phosphorescence (BRTP) emission faces forbidden challenges due to difficulties in generating high‐energy triplet excitons and their sensitivity. Herein, a covalently crosslinked purely organic material (BOP@BA) is prepared from boric acid (BA) and 3,5‐dicarboxyphenylboronic acid (BOP) via a simple dehydration reaction. This material exhibits pure deep blue room‐temperature phosphorescence (RTP) with a lifetime of 2.45 s. Unlike individual BA or BOP, dehydrated BOP@BA exhibits a hypsochromic shift to 415 nm, yielding a purely deep‐blue RTP. Meanwhile, the formed covalent skeleton protects the high‐energy triplet excitons from nonradiative deactivation, thereby elongating the lifetime to 2.45 s. Significantly, lanthanide ions (Ln 3+ : Eu 3+ and Tb 3+ ), acting as fine controllers, enable precise tuning of the lifetime through supramolecular coordination and energy transfer, with a precision of as low as 0.1 s and an effective range of 1.71–2.45 s. This work is expected to provide a feasible strategy for constructing ultralong BRTP materials and achieving precise luminescence manipulation.