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.