One-Pot Synthesis of Bis(arylamino)pentiptycenes by TiCl4-DABCO Assisted Reductive Amination of Pentiptycene Quinone.

The previously eight-step synthesis of bis(arylamino)pentiptycenes (2) from pentiptycene quinone (1) can now be achieved in a single step with 18-90% yields through TiCl4-DABCO assisted reductive amination with anilines. Both the dual amination of 1 and the in situ reduction of quinone diimines are unprecedented. The π system of 2 can be further expanded, including the formation of bis(diarylamino)pentiptycenes. This work also provides mechanistic insights into the challenges encountered in the dual reductive amination of 1 with other amines.

Porous Supramolecular Assembly of Pentiptycene-Containing Gold(I) Complexes: Persistent Excited-State Aurophilicity and Inclusion-Induced Emission Enhancement.

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 Au4 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.

A polymorphic pentiptycene-containing gold(I) isocyanide complex: solvent- and conformation-dependent supramolecular luminescence.

Four crystalline (pseudo)polymorphs of [Ph-Au-C[triple bond, length as m-dash]N-Phip-OC8H17] (1), where Phip = central phenylene of pentiptycene, reveal that the π-backbone conformation relative to the AuAu bonding axis is important in determining the energy and efficiency of the supramolecular luminescence, which offers mechanistic insights into the luminescence mechanochromism and vapochromism and the solvent-dependent aggregation-induced emission (AIE) of 1.

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

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.

A dual fluorescent/phosphorescent zincophosphite with interesting water adsorption and structural transformation properties.

A dual fluorescent/phosphorescent solid was produced using the triazole-assisted synthesis method under hydro(solvo)thermal conditions. The title compound emitted blue luminescence that turned green when UV irradiation was stopped. It also exhibited stable PL properties with good thermal and photostability. Furthermore, the 3D inorganic skeleton in NTOU-6 underwent structural transformation into another inorganic metallophosphite solid (NTOU-6b) and water adsorption was observed during this process of structural reconstruction. The detailed structural features of both compounds were also determined by single-crystal X-ray diffraction. This is a very rare example of a metallophosphite with the interesting properties of luminescence color switching (blue to green), water adsorption, and structural transformation. The synthesis, structural diversity, adsorption, material stability, and luminescence properties were also discussed.

Iptycene substitution enhances the electrochemical activity and stability of polyanilines.

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.

Photomechanochromic vs. mechanochromic fluorescence of a unichromophoric bimodal molecular solid: multicolour fluorescence patterning.

Mechanofluorochromism (MFC) of molecular solids generally results from the variation of intermolecular interactions induced by external mechanical forces. However, the use of internal photomechanical forces to perturb intermolecular interactions for multicolour fluorescence responses has yet to be demonstrated. Herein we report a unichromophoric anthracene-pentiptycene derivative (1) that displays both MFC and photomechanofluorochromism (PMFC), which lead to various fluorescence colours including red-green-blue (RGB) and near-pure white-light emission. Compound 1 crystallizes in two polymorphs, the yellow (Y) and green (G) emissive forms, in which the pairwise stacked anthracene groups undergo [4 + 4] photodimerization to form the UV (black) emissive photodimer 2 and meanwhile exert photomechanical stresses on the neighbouring molecules. While the photomechanical stresses cause an excimer-to-monomer switching that results in a blue fluorescent state for the Y form, a red-emissive "super dimer" is photomechanically produced for the G form. The recovery of the Y form demands heating, but the G form could be restored by selective photoexcitation of the super dimer. X-ray crystal structures of the Y and G forms and the photodimer 2 generated through single-crystal-to-single-crystal transformation provide a clue to the origins of polymorph-dependent PMFC. The corresponding MFC and mechano-activated vapofluorochromism (VFC) of 1 also shed light on the structure-property relationship. The ability to spatially and temporally control the fluorochromicity of 1 is demonstrated by a series of multicolour fluorescence patterning of "angelfishes".

The spectral heterogeneity and size distribution of the carbon dots derived from time-resolved fluorescence studies.

We performed comprehensive studies on the photoluminescence properties of the carbon dots prepared from citric acid (C-dotsCA) and citric acid + ethylenediamine (C-dotsCA+EDA). The cryogenic experiment confirmed that the excitation dependent fluorescence and the spectral relaxation dynamics of the C-dots are associated with the presence of multiple emissive states/species in the C-dots instead of solvation dynamics. Moreover, we also compared the size of the C-dots estimated from the TEM/AFM images and fluorescence anisotropy methods. The experimental results indicate that the fluorescence anisotropy method not only avoids the formation of aggregates during the sample preparation processes, but also selectively detects the size of emissive C-dots in the solution. Therefore, the fluorescence anisotropy method is ideal for studying the size dependent optical properties of the C-dots.