Synergistic Diphenylboron and Heavy‐Atom Effect: A BF ₂ ‐Free Strategy for Four‐Coordinated Boron Room‐Temperature Phosphorescence

Purely organic room‐temperature phosphorescence (RTP) materials based on four‐coordinated boron are predominantly centered on the boron difluoride (BF 2 ) unit, leveraging its strong rigidification effect. Herein, a diphenylboron (BPh 2 ) and heavy‐atom synergistic strategy, constructing a BF 2 ‐free four‐coordinated boron RTP material (PMB‐Br), is presented. The introduction of the bromine atom endows the powder samples with green phosphorescence featuring a lifetime of 1.72 ms. Theoretical calculations reveal that the bromine atom intramolecularly enhances the key spin‐orbit coupling (SOC) constant to 16.13 cm −1 , providing the core driving force for efficient intersystem crossing; simultaneously, it intermolecularly cooperates with BPh 2 to construct a rigid network that stabilizes the excitons. A comparison with the isostructural BF 2 analogue (PMB‐BF 2 , SOC of merely 0.63 cm −1 ) demonstrates that the BPh 2 unit, due to its ability to induce an S 1 (CT)/T 2 (CT+LE) excited‐state configuration, possesses a more pronounced synergy with the heavy‐atom effect to enhance SOC. Based on this, a complementary dual‐pathway model for four‐coordinated boron RTP is tentatively proposed. Alongside the rigidification‐predominated BF 2 ‐based strategy, the BPh 2 pathway exemplifies a potential complementary SOC–predominated strategy, providing a new perspective for the future exploration beyond the established BF 2 ‐centric design paradigm.