Through-Space Electron Effect Regulated Selective Expression of Ultralong Organic Room Temperature Phosphorescence and Photochromism

We report a through-space electron effect (TSEE) between two phosphorescent units that significantly modulates the selective expression of ultralong organic room-temperature phosphorescence (UORTP) and photochromism. A series of phosphorescent molecules (DNapTr, DNapBNT, DNapFL, and DNapPy), featuring two phosphorescent units connected by a nonconjugated spacer, were synthesized. Our findings reveal that both TSEE and the energy gap Δ<i>E</i> (defined as <i>E</i>_PU2 - <i>E</i>_PU1) between the lowest triplet energy levels (T₁) of the phosphorescent units play crucial roles in determining UORTP and the photochromic behavior in PMMA films. NMR spectra and molecular simulations confirm the presence of TSEE, with their strength ranked as DNapPy < DNapFL < DNapBNT in the presence of TSEE. The DNap unit is governed by TSEE, where moderate TSEE inhibits radical cation formation, while strong TSEE promotes it. Consequently, DNapTr, DNapBNT, and DNapFL exhibit tunable photochromism, whereas DNapPy remains nonphotochromic. UORTP is jointly influenced by TSEE and Δ<i>E</i>. For DNapTr (Δ<i>E</i> > 0), excitons are trapped by DNap via TSEE, leading to UORTP from DNap. In DNapBNT and DNapFL (Δ<i>E</i> slightly <0), strong TSEE directs UORTP to PU2. In DNapPy (Δ<i>E</i> ≪ 0), moderate TSEE enables UORTP from both DNap and Py. By leveraging TSEE and tuning T₁ of PU2, we successfully modulated both photochromism and UORTP. This study provides a strategy for designing intelligent organic phosphorescent materials.