Ionic-to-coordinate structural transformation of hybrid metal halides with improved anti-Kasha room-temperature phosphorescence and dynamic multicolor emission

Abstract

Hybrid metal halides (HMHs) have emerged as promising platforms for room-temperature phosphorescence (RTP) due to their structural tunability and excited-state dynamics. However, the distinct roles of ionic versus coordinate assembly in governing RTP behavior remain unexplored. Herein, we report a thermally induced single-crystal-to-single-crystal (SCSC) transformation from ionic (DPTAH₃)InCl₆·2.5H₂O (In-1, DPTA = 3,5-di(1H-pyrazol-4-yl)-4H-1,2,4-triazol-4-amine) to ionic (DPTAH₃)InCl₆ (In-2) and finally to coordinate (DPTAH)InCl₄ (In-3). This stepwise transition enables a systematic investigation of the structure–optical properties. In detail, all three samples exhibit anti-Kasha RTP due to the fast relaxation of excitons via T₂ → S₀ and efficient reverse internal conversion from T₁ to T₂. Coordinate In-3 shows improved anti-Kasha RTP performance, resulting from the synergistic effects of improved structural rigidity and heavy-atom-enhanced ISC from S₁ → T₂ and T₃. Ionic In-1 and In-2 exhibit a higher Sb³⁺ doping efficiency, with a near-unity photoluminescence quantum yield, due to their ionic nature. Additionally, these three samples show excitation-dependent multicolor emissions and dynamic RTP behavior because of the twisted intramolecular charge transfer of DPTA and triplet energy transfer from DPTA to Sb³⁺. These advantages enable advanced applications in white-light LED and time-resolved anti-counterfeiting. This work provides a mechanistic understanding of how assembly modes govern RTP and offers a design strategy for luminescent materials.