Tuning Triplet Exciton Pathways via Molecular Aggregation in a Family of Coordination Polymers.

Molecular aggregation is the key factor in determining the triplet exciton pathways of room-temperature phosphorescence (RTP) materials; however, controlling different aggregation forms and understanding their synergistic effects remain challenging. In this work, we report three coordination polymers (CPs) with cofacial translational stacking (H-aggregation), cofacial-staggered translational stacking (H-J aggregation) and cofacial translational-crossing stacking (H-X aggregation): [Zn(3,4-PyDC)(TPT)]·TPT (1; 3,4-PyDC = 3,4-pyridinedicarboxylate; TPT = 2,4,6-tri(4-pyridyl)-1,3,5-triazine), [Zn(IPA)(TPT)2]·H2O (2; IPA = isophthalate) and [Zn3(3,5-PyC)2(TPT)3(H2O)2] (3; 3,5-PyC = 3,5-pyrazoledicarboxylate). By changing the aggregation modes, these CPs exhibit tunable triplet exciton pathways, enabling distinct fluorescent, phosphorescent, and photochromic properties. Single-crystal X-ray diffraction, time-resolved emission spectroscopy and theoretical analysis demonstrate that enhanced charge migration in 2 with H-J aggregation promotes charge-separated photochromism, while differentiated orbital energies in 3 with H-X aggregation enables wavelength-responsive room temperature phosphorescence. These findings provide a route to hybrid CPs with designated triplet-exciton pathways and associated optical properties by manipulating molecular aggregation.