Steric Engineering of Cyclometalated Pt(II) Complexes toward High-Contrast Monomer–Excimer-Based Mechanochromic and Vapochromic Luminescence

• Published in: Inorganic chemistry Vol. 59; no. 16; pp. 11584 - 11594
• Main Authors: Lien, Chen-Yu, Hsu, Ying-Feng, Liu, Yi-Hung, Peng, Shie-Ming, Shinmyozu, Teruo, Yang, Jye-Shane
• Format: Journal Article
• Language: English
• Published: American Chemical Society 17.08.2020
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.0c01390

Ligands play a crucial role in the supramolecular photoluminescence properties of Pt­(II) square-planar complexes. To improve the luminescence color responses of N∧C∧N cyclometalated Pt­(II) complexes to external stimuli such as mechanical stress and chemical vapors, we have conducted a steric engineering of the previous systems 1a–1d [Inorg. Chem. 2017, 56, 4978–4989] by introducing two tert-butyl groups to the tridentate ligand to form complexes 2a–2c. Unlike the “too low” or “too high” steric hindrance of the NCNPt core in 1a–1d, the combined steric effects of the tert-butyl groups at one side and the pentiptycene group at the other side of the NCNPt core in 2b are “just right” for generating as-prepared powders with pure monomer (green) emission or pure excimer (red) emission, depending on the rate of precipitation from solutions. The synergistic steric effects are also beneficial to the solid-state luminescence quantum efficiency (30–36%). As a result of the differences in steric interactions and thus in the relative monomer vs excimer emission intensity, each complex of 2a–2c performs a two-step luminescence mechanochromism and vapochromism with different color patterns. This work provides an intriguing example of steric engineering of Pt­(II) complexes toward highly emissive molecular solids with high-contrast mechanochromic and vapochromic luminescence.