Control of Pt···Pt interactions in Pt(II) complex crystals as luminescence sensors for the detection of external stimuli: recent achievements and perspectives.

This review summarizes recent advances in the control of the luminescent chromic behavior of Pt(II) complex crystals, focusing on the design strategies of their molecular and packing structures. Square-planar Pt(II) complexes exhibit unique chromic luminescence owing to flexible Pt···Pt interactions, enabling their use as highly sensitive optical sensors to visualize external stimuli and environmental changes. However, the energy of the Pt···Pt interaction is relatively weak, making it difficult to precisely design and control the chromic luminescence based on the Pt···Pt interactions. This review discusses the challenging control of Pt···Pt interactions based on molecular assembly and presents design strategies using hydrogen bonding, halogen interactions, π-π stacking, and ion-pairing and counterion effects, with specific examples for each approach. Future research will focus on expanding analytical approaches, integrating these materials into sensing devices, and exploring synergies between chromic luminescence and other physical properties such as magnetism and conductivity. These advancements are expected to lead to innovative sensing technologies and significant breakthroughs in analytical chemistry and materials science.