Excimer-Monomer Photoluminescence Mechanochromism and Vapochromism of Pentiptycene-Containing Cyclometalated Platinum(II) Complexes Che-Jen Lin, Yi-Hung Liu, Shie-Ming Peng, Teruo Shinmyozu, and Jye-Shane Yang* Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan * S Supporting Information ABSTRACT: The ability of the bulky H-shaped pentiptycene scaffold in promoting the mechanochromic and vapochromic luminescence properties for organometallic materials has been demonstrated with the N^C^N cyclometalated platinum(II) complexes [X-NCNPtY], where X = Br or Pa, the substituent on the terdentate dipyridylbenzene N^C^N ligand, and Y = Cl or Pa, the ancillary ligand, in which Pa = pentiptycene acetylene. Intermolecular interactions between the planar NCNPt cores are described by π-π and d-π interactions with negligible Pt II ···Pt II bonding, corresponding to ligand-centered excimer rather than metal -metal-to-ligand charge-transfer emission, for these platinum(II) complexes in aggregates and in the solid state. Interplay of the relative excimer-to-monomer emission intensity in response to external force and/or vapor stimuli accounts for the luminescence mechanochromism and vapochromism of the pentiptycene-incorporated platinum(II) complexes [Pa- NCNPtCl], [Br-NCNPtPa], and [Pa-NCNPtPa], whereas the pentiptycene-free counterpart [Br-NCNPtCl] undergoes little or no emission color response. In particular, the complex [Pa-NCNPtCl] displays a distinct response to aromatic versus nonaromatic organic vapors: namely, aromatic vapors such as benzene convert the excimer emission to monomer emission, but the opposite is true with nonaromatic vapors. A two-stage emission color change from red to orange and then to yellow could thus be achieved by grinding and by subsequent benzene-vapor fuming. Another feature associated with [Pa-NCNPtCl] is an aggregation-induced green → magenta luminescence color change in water/tetrahydrofuran mixed solutions. The structure- luminescence property relationship is discussed in relation to intermolecular interactions and packing modes that depend on the number and positions of pentiptycene groups. 1. INTRODUCTION Cyclometalated platinum(II) complexes have attracted much attention because of their intriguing photoluminescent and photoresponsive supramolecular properties. 1-7 The square- planar coordination geometry of the platinum center as well as the flat π ligands allows intermolecular Pt II ···Pt II and π-π interactions, which could drive self-assembly in solution and the solid state and thus switch the monomer emission to red- shifted metal-metal-to-ligand charge-transfer (MMLCT) or excimer (excited-state dimer) emission. 8,9 When the Pt II ···Pt II or π-π interactions are susceptible to external perturbations such as mechanical stress and chemical vapors, the correspond- ing systems would display mechanochromic and vapochromic luminescence properties and hold great promise as sensory materials. 9-20 Pentiptycene is a rigid H-shaped molecule, in which the central phenylene ring is sterically shielded by the two V- shaped “iptycenyl” substituents. 21 Pentiptycene has been incorporated into π-conjugated organic or organometallic systems such as platinum acetylides 22-24 and oligo- 25-27 and poly(aryleneethynylene)s 28-30 to diminish intermolecular π- stacking interactions and thus improve the photoluminescence quantum efficiency in aggregates, powders, and thin solid films; the putative porous structures created by the stacked pentiptycene scaffolds could also facilitate interactions with chemical vapors for photoluminescence quenching. 24,28-30 Recently, we demonstrated a new function of pentiptycene, that is, promoting both mechanochromic and vapochromic luminescence for organic π systems toward multicolor and multicomponent responses. 31 This finding has prompted us to investigate the corresponding performance of pentiptycene in photoluminescent orgaometallic platinum(II) complexes. We report herein the mechanochromic and vapochromic luminescence properties of pentiptycene-containing cyclo- metalated platinum(II) complexes [Br-NCNPtPa], [Pa- NCNPtCl], and [Pa-NCNPtPa], in which NCN stands for the terdentate 1,3-bis(2-pyridyl)benzene N^C^N ligand and Pa the pentiptyceneacetylene (PaH) group (Chart 1). The pentiptycene-free system [Br-NCNPtCl] was also prepared as a reference for the discussion of the pentiptycene effect. Both the X-ray crystallographic and electronic spectroscopic data Received: January 3, 2017 Published: April 13, 2017 Article pubs.acs.org/IC © 2017 American Chemical Society 4978 DOI: 10.1021/acs.inorgchem.7b00009 Inorg. Chem. 2017, 56, 4978-4989