Achieving T-Type Photochromism through Generating Copper(I) Metallacyclopentadiene Biradical

Abstract

Photochromism due to organometallic ring-closure through CC linkage has not been attained ever before. In this work, we report an initial approach to achieve T-type photochromism by creating metallacyclopentadiene biradical under light irradiation. A class of CuPt 2 phenylacetylide compounds were prepared with distinguished photochromic recyclability and durability, which involve the formation of thermally sensitive copper(I)-butadienyl five-membered ring through copper(I)participated ring-closure. Upon UV light irradiation, metallacyclopentadiene with copper(I) center chelated by 1,3-butadiene-1,4-diyl biradical is generated through photochemical C-C linkage of two face-to-face oriented ethynyl units in close proximity, which gives rise to a drastic change in UV-Vis absorption spectrum. When UV light irradiation is ceased, decoloration occurs through thermal cycloreversion, which endows photochromic CuPt 2 complexes with self-recovery characteristics.Electron paramagnetic resonance (EPR) spectral study confirms a biradical feature of the ring-closed isomer. The thermal decoloration half-lives at ambient temperature are regulated from seconds to hours by increasing F substituents in phenylethynyl ligands.

Attaining Exceptional Stable Copper(I) Metallacyclopentadiene Diradicaloids through Ligand Engineering

“…Of the four CCC 6 F 5 ligands, two of them are far away from each other, whereas the other two are face-to-face arranged in close proximity with ca. 3.4 Å distance between two C 6 F 5 planes, implying the presence of a significant intramolecular π–π interaction between them . As shown in Figure a, the face-to-face arranged CCC 6 F 5 ligands in CuPt 2 complex 1 facilitate the two ethynyls (CC) to arrange side by side with a distance of C42···C91 of 3.51 Å.…”

“…The 19 F NMR spectroscopy gives valuable information for the comparison of the structural features between complexes 1−6 and the corresponding diradicaloids 1c−6c. As depicted 3a) uncovers triplet-state characteristics of the diradicals.…”

“…As a result, the elaborate design of triphosphine ligands makes it feasible to accomplish fully spectroscopic and electrochemical characterization of these ultrastable copper(I) metallacyclopentadiene diradicaloids as well as exploit their potential applications in electronic and optoelectronic fields. 19 As shown in Figure 1a, the face-to-face arranged C�CC 6 F 5 ligands in CuPt 2 complex 1 facilitate the two ethynyls (C�C) to arrange side by side with a distance of C42•••C91 of 3.51 Å. Undoubtedly, such a side-by-side orientation facilitates them to connect through the C ethynyl −C ethynyl bond for generating ringclosed isomer 1c upon UV light irradiation as indicated in Figure 1b.…”

“…15−19 We uncovered recently that triphosphine-sustained Pt 2 Cu complexes [Pt 2 Cu(dpmp) 2 (C�CR) 4 ] + (dpmp = bis-(diphenylphosphinomethyl)phenylphosphine, R = phenyl derivatives) show unconventional T-type photochromism through the formation of copper(I) metallacyclopentadiene diradicals. 19 Based on this finding, we are devoted to establishing a photochemically synthetic approach for this new class of diradicaloids, which are likely stabilized through ligand engineering to delocalize unpaired electrons and increase half-lives. In this work, we successfully obtain a series of ultrastable diradicaloids of copper(I) metallacyclopentadienes (Scheme 1) by introducing electron-deficient groups to triphosphine ligand with a half-life to be as long as ca.…”

“…The different degree of overlapping between metal orbitals and molecular orbitals of 1,3-butadienyl moieties endows them with some degree of π-conjugation as well as specific chemical reactivity, which makes them not only serve as reactive intermediates useful for chemical transformation in organic synthesis but also as a family of potential semiconductor and photoelectric materials useful in the optoelectronic field. − In striking contrast to organic five-membered heterocycles, metallacyclopentadienes are mostly unstable under ambient conditions due to their high reactivity. In many cases, they are sensitive to heat, air, and moisture because the much longer M–C bonds than C–C ones as well as the significantly smaller C–M–C angle than that of C–C–C result in large tension to destabilize metallacycles so that they are difficultly accessible through conventional synthetic procedures. − …”