Multistate and Multicolor Photochromism through Selective Cycloreversion in Asymmetric Platinum(II) Complexes with Two Different Dithienylethene–Acetylides

Photocontrolled multiple-state photochromic benzo[b]phosphole thieno[3,2-b]phosphole-containing alkynylgold(I) complex via selective light irradiation

Photochromic materials have drawn growing attention because using light as a stimulus has been regarded as a convenient and environmental-friendly way to control properties of smart materials. While photoresponsive systems that are capable of showing multiple-state photochromism are attractive, the development of materials with such capabilities has remained a challenging task. Here we show that a benzo[b]phosphole thieno[3,2‑b]phosphole-containing alkynylgold(I) complex features multiple photoinduced color changes, in which the gold(I) metal center plays an important role in separating two photoactive units that leads to the suppression of intramolecular quenching processes of the excited states. More importantly, the exclusive photochemical reactivity of the thieno[3,2‑b]phosphole moiety of the gold(I) complex can be initiated upon photoirradiation of visible light. Stepwise photochromism of the gold(I) complex has been made possible, offering an effective strategy for the construction of multiple-state photochromic materials with multiple photocontrolled states to enhance the storage capacity of potential optical memory devices.

Two cyclometalated Pt(ii) complexes showing reversible phosphorescence switching due to grinding-induced destruction and crystallization-induced formation of supramolecular dimer structure

Two Pt(ii) complexes 1 and 2 reveal similar supramolecular dimer structure, in which two [Pt(dfppy/ppy)(pbdtmi)]+ cations connect each other through the π⋯π stacking interaction. Thus these complexes show reversible phosphorescence switching by grinding and crystallization with toluene.

Regulation of the Switchable Luminescence of Tridentate Platinum(II) Complexes by Photoisomerization

Organoplatinum (II) complexes are promising candidates for the construction of smart supramolecular materials due to their unique flat structures. This accompanied by intriguing luminescent properties, prompts the molecules to aggregate after external stimuli. Nevertheless, the utilization of photo-responsive subunits to modulate their assemble behaviors and functions are still rarely explored. In this work, azobenzene (azo)-appended tridentate platinum (II) complexes with different linkers have been designed and synthesized. The intermolecular hydrogen bonding, π-π stacking, and metal-metal interactions were finely controlled through the tiny alteration of the linkers, which was found to play a vital role in self-assembly, and photophysical and photoisomerization properties. Some of them exhibited dual emission bands originating from metal-perturbed triplet intraligand (3IL) and metal-metal to ligand charge transfer (3MMLCT) excited states due to the different intermolecular interactions. Based on this, the manipulation of switchable luminescence as well as the controllable morphologies have been realized by photoisomerization.

Synthesis, Photophysical, Photochromic, and Photomodulated Resistive Memory Studies of Dithienylethene-Containing Copper(I) Diimine Complexes

A series of dithienylethene-containing copper(I) diimine complexes have been synthesized and structurally characterized. Systematic studies on their photophysics, electrochemistry, and photochromism have been carried out. The photoinduced color changes of the copper(I) complexes have been achieved by photoexcitation into the metal-to-ligand charge-transfer (MLCT) absorption bands, indicating the photosensitization of light-induced cyclization by the ³MLCT excited state. In addition, by an increase in either the steric bulkiness around the copper(I) center or the structural rigidity of the complexes, the quantum efficiencies of photoluminescence and photocyclization can be effectively enhanced because of suppression of the flattening distortion of the complexes at the MLCT excited state. Furthermore, one of the complexes has been employed as an active component in the fabrication of solution-processed resistive memory devices. Notable lowering of the switching threshold voltage of the binary memory devices has been realized through photocyclization of the dithienylethene-containing copper(I) system.

Photoisomerization of PtII Complexes Containing Two Different Photochromic Chromophores: Boron Chromophore versus Dithienylethene Chromophore

In order to examine competitive photoisomerization, a series of novel photochromic Pt^II molecules that contain both dithienylethene (DTE) and B(ppy)Mes₂ units (ppy=2-phenylpyridine, Mes=mesityl) were successfully synthesized and fully structurally characterized. Their photochromic properties were examined by UV/Vis, emission and NMR spectroscopy. It was found that the DTE unit in all three compounds is the preferred photoisomerization site, exhibiting reversible photochromism with irradiation. The B(ppy)Mes₂ unit does not undergo photoisomerization in these molecules, but likely enhances the photoisomerization quantum efficiency of the DTE moiety through the antenna effect. Extended irradiation with UV light leads to the rearrangement of the ring-closed isomers of DTE. TD-DFT computational studies indicate that the DTE photocyclization proceeds via a triplet pathway through an efficient energy transfer process.

A colorimetric and fluorescent chemosensor for Hg2+ based on a photochromic diarylethene with a quinoline unit

A new colorimetric and fluorescent 'on-off' chemosensor, 1O, based on a photochromic diarylethene with a quinoline unit was designed and synthesized. The chemosensor 1O demonstrated selective and sensitive detection of Hg2+ ions in the presence of other competitive metal ions in acetonitrile. The stoichiometric ratio of the sensor 1O for Hg2+ was determined to be 1 : 1, and the limit of detection of the probe 1O was calculated to be 56.3 nM for Hg2+. In addition, a molecular logic circuit with four inputs and one output was successfully constructed with UV/vis light and metal-responsive behavior. ESI-MS spectroscopy, Job's plot analysis, and 1H NMR titration experiments confirm the binding behavior between 1O and Hg2+.

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

A highly selective fluorescent probe for detection of Cd2+ and HSO3− based on photochromic diarylethene with a triazole-bridged coumarin-quinoline group

A novel photochromic diarylethene containing a quinoline-linked 3-aminocoumarin Schiff base unit (1O) was synthesized and used for the selective detection of Cd²⁺ and HSO₃⁻. The synthesized probe exhibited a straightforward response for the selective detection of Cd²⁺. Its fluorescence emission red-shifted ∼126 nm and was enhanced 24.9 fold in the presence of Cd²⁺. Meanwhile, the fluorescence color of 1O changed from dark cyan to golden yellow. The binding stoichiometry between 1O and Cd²⁺ was determined to be 1 : 1. A molecular logic circuit with three inputs and one output was successfully constructed with its light and metal-responsive behaviors. In addition, 1O was able to selectively recognize HSO₃⁻ with a 135-fold enhanced fluorescence emission and a notable fluorescence color change from dark cyan to bright cyan. The ¹H NMR and mass spectrometry analyses suggest that the HSO₃⁻ sensing of 1O is based on the hydrolysis of the Schiff base group of 1O.

A novel photochromic diarylethene containing a quinoline-linked 3-aminocoumarin Schiff base unit (1O) was synthesized and used for the selective detection of Cd²⁺ and HSO₃⁻.

Multiphotochromism in an Asymmetric Ruthenium Complex with Two Different Dithienylethenes

An asymmetric bis(dithienylethene-acetylide) ruthenium(II) complex trans-Ru(dppe)₂(L1o)(L2o) (1oo) incorporating two different dithienylethene-acetylides (L1o and L2o) was designed to modulate multistate photochromism in view of the well separated ring-closing absorption bands between L1o and L2o. Upon irradiation with appropriate wavelengths of light, complex 1 undergoes stepwise photocyclization and selective photocycloreversion to afford four states (1oo, 1co, 1oc, and 1cc). As a contrast, symmetric complexes trans-Ru(dppe)₂(L1o)₂ (2oo) and trans-Ru(dppe)₂(L2o)₂ (3oo) with two identical dithienylethene-acetylides were synthesized, and the corresponding photochromic behavior was investigated. The photochromic properties of the oxidized species (1oo⁺/1co⁺/1oc⁺/1cc⁺, 2oo⁺/2co⁺/2cc⁺, and 3oo⁺/3co⁺/3cc⁺) were also investigated. The ring-closing absorption bands of one-electron oxidized species 1oo⁺, 2oo⁺, and 3oo⁺ show obvious blue shifts relative to those of 1oo, 2oo, and 3oo, respectively. The ring-closing absorption bands in both neutral and oxidized species grow progressively following oo → oc/co → cc and oo⁺ → oc⁺/co⁺ → cc⁺. As revealed by spectroscopic, electrochemical, and computational studies, complex 1 displays eight switchable states through stepwise photocyclization, selective cycloreversion, and a reversible redox process.