Topochemical photocycloaddition in two-dimensional lead-halide coordination polymers with tunable phosphorescence.

Topochemical transformation in which the parent structural motifs are preserved has become a powerful strategy to access new advanced materials. Solid-state topochemical conversion in a single-crystal-to-single-crystal (SCSC) fashion is particularly attractive as it provides design principles with unequivocal structural details. Here, we report a series of two-dimensional (2D) lead-halide coordination polymers with bipyridyl ethylene (bpe) ligands that can undergo quantitative SCSC [2 + 2] photocycloaddition. The chemical and structural diversity of 2D lead-halide coordination polymers allows systematic modulation of the rate of SCSC [2 + 2] photocycloaddition by changing the halide and bpe ligands. Our work reveals the structure-property relationship in lead-halide coordination polymers during the dynamic [2 + 2] photocycloaddition process. The photo-transformed coordination polymers with cyclobutane linkages show drastically different properties in optical absorption and emission. We present a viable strategy to modify the structure and properties of lead-halide coordination polymers by post-synthetic modification.