The multicolour fluorescence responses to external mechanical forces vs. internal photomechanical stresses of a molecular solid are demonstrated and compared.

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.

We report herein a porous supramolecular framework formed by a linear mononuclear Au(I) complex (1) via the tongue-and-groove-like joinery between the pentiptycene U-cavities (grooves) and the rod-shaped π-conjugated backbone and alkyl chains (tongues) with the assistance of C−H•••π and aurophilic interactions. The framework contains distorted tetrahedral Au 4 units, which undergo stepwise and persistent photoinduced Au(I)− Au(I) bond shortening (excited-state aurophilicity), leading to multicolored luminescence photochromism. The one-dimensional pore channels could accommodate different solvates and guests, and the guest inclusion-induced luminescence enhancement (up to 300%) and/or vapochromism are characterized. A correlation between the aurophilic bonding and the luminescence activity is uncovered by TDDFT calculations. Isostructural derivatives 2 and 3 corroborate both the robustness of the porous supramolecular assembly and the mechanisms of the stimulation-induced luminescence properties of 1. This work demonstrates the cooperation of aurophilicity and structural porosity and adaptability in achieving novel supramolecular photochemical properties.

The electrochemical stability of polyaniline (PANI) films is a key issue for their application as electrode materials. This work demonstrates that a low fraction (<5%) of pentiptycene incorporation of the PANI conjugated backbone could significantly enhance the capacitive performance and charge-discharge cycling stability of PANI films, attributable to the clipping effect of pentiptycene cavities that restricts motional freedom of polymer chains and promotes interchain conductivity.

Four crystalline (pseudo)polymorphs of [Ph−Au−C≡N−Phip−OC8H17] (1), where Phip = central phenylene of pentiptycene, reveal that the π-backbone conformation relative to the Au∙∙∙Au bonding axis is important in determining the energy...

Understanding the crystal packing behavior of a luminescent π‐conjugated system would facilitate the design of crystals of the desired luminescence properties. Crystal pseudopolymorphism provides a great opportunity for such a purpose and meanwhile for tuning the solid‐state luminescence properties of a molecular system via crystallization in different solvents. Herein, we report an example of structural modification that converts a polymorphic anthracene‐pentiptycene π‐system (1) into a pseudopolymorphic counterpart (2), which displays polymorph‐dependent fluorescence color and [4 + 4] photodimerization activity. The five pseudopolymorphs of 2 (crystal notation 2/Solvent, and Solvent = THF, Hex, CHCl3, DCM, and MeOH) have a common feature of forming one‐dimensional (1D) columnar alkyl‐pentiptycene threading mode. The subsequent packing of the 1D columns depends on the size of the included solvents, leading to two major types of pentiptycene‐based framework. One of the frameworks possesses 1D solvent channels that account for 14–18% of the unit cell volume, and the other type has small solvent cavities. A crystal with partial hexane inclusion (i.e., 2/Hex') is also obtained, which provides insights into the stability of the apohost structure. Intriguing solvent guest effects on the fluorescence properties of 2/Solvent are also noted.

Because of the ultrafast C=C bond torsion and electrocyclic reaction in the excited state, cis‐stilbenes are generally nonfluorescent (Φf <10−4) in common solvents at ambient temperature. The known examples of highly fluorescent cis‐stilbenes are limited to those with the C=C configuration structurally locked. Herein we report a novel cis‐stiff‐stilbene c‐2 a that displays a high fluorescence quantum efficiency up to 0.47 in acetonitrile (MeCN) without sacrificing the photoisomerization ability. Through comparison with the corresponding aminostilbene c‐1 and positional isomer c‐2 b, the fluorescence turn‐on for c‐2 a takes root in two structural origins: namely, a rigid stilbene backbone that suppresses the cis→dihydrophenanthrene (DHP) photocyclization and a non‐twisted meta‐N,N‐dimethylamino (DMA) substituent that slows down the cis→trans photoisomerization. The corresponding trans isomers t‐1, t‐2 a, and t‐2 b are also investigated to gain insights into the meta‐DMA effect in stiff‐stilbene.

This is a very rare example of a crystalline metallophosphite/phosphate framework with structural transformation, water adsorption, and luminescence color switching (blue to green).