Photoluminescence Switching of Azobenzene-Conjugated Pt(II) Terpyridine Complexes by Trans−Cis Photoisomerization

Abstract

Pt(II) complexes with a terpyridylazobenzene ligand (tpyAB) were newly synthesized, and their photoluminescence properties by trans-cis isomerization of the azo moiety were investigated. In these complexes, upon excitation with 366-nm light in polar solvents such as DMF, DMSO, and propylene carbonate, trans-to-cis isomerization with significant UV-vis spectral changes occurred almost completely. Cis-to-trans isomerization was observed both by irradiation with visible light and by heat. The reduction peaks due to the terpyridine and the azo group in the cyclic voltammograms of the Pt complexes were shifted in the positive direction by trans-to-cis isomerization. Emission spectral changes due to trans-cis isomerization were observed for both the tpyAB and the Pt complexes. The significant differences in the emission properties of the complex compared to tpyAB include the observation that both the excitation and emission wavelengths were shifted to lower energy, located in the visible region. Moreover, the change in emission intensity between the trans and cis forms was more significant upon excitation with UV light, because the trans form of the complexes showed absolutely no emission. Accordingly, the azobenzene-conjugated Pt(II) terpyridine complexes promise to be doubly photofunctional materials, showing complete off-on switching of emission linked to the trans-cis conformation change.

Square-Planar Pd(II), Pt(II), and Au(III) Terpyridine Complexes: Their Syntheses, Physical Properties, Supramolecular Constructs, and Biomedical Activities

“…Complexes 5-7 containing the electron-withdrawing cyano moiety and electron-donating NMe 2 and SMe groups exhibited luminescence at 25°C with excited-state lifetimes of 116,1920, and 146 ns, respectively. 49 It was proposed that the cyano group in complex 5 activated the 3 MLCT band by decreasing its energy level and increasing the gap between 3 d-d and 3 MLCT, whereas the NMe 2 group in 6 induced the luminescence Via mixing the 3 MLCT and triplet intraligand charge-transfer ( 3 ILCT) transitions ( Figure 14A).…”

Photoisomerisation in Aminoazobenzene‐Substituted Ruthenium(II) Tris(bipyridine) Complexes: Influence of the Conjugation Pathway

“…Interestingly, the phosphorescence properties of the complexes in deoxygenated THF are only slightly affected by the trans ‐to‐ cis photoisomerisation (Supporting Information, Figure S6) 6c. 7a, 27 This observation is in line with the fact that the lowest triplet state is the 3 MLCT, which excludes any triplet–triplet energy transfer to the azo photochromic moiety. This suggests that the significant decrease of Φ t→c observed for Ru L1 – L3 presumably stems from this competing deactivation channel to the 3 MLCT state, as depicted in Scheme .…”

“…For instance, this has already been implemented by linking the azo unit to a polypyridine and coordinating the resulting ligand to a transition‐metal atom 7. Some of these complexes show photochromism7c or luminescence switching upon irradiation 7a. 8 Although isomerisation is assumed to take place from intraligand excited states localised on the azobenzene unit, the choice of the metal centre is known to drive the photochromic properties of the azobenzene unit 7a.…”

“…Some of these complexes show photochromism7c or luminescence switching upon irradiation 7a. 8 Although isomerisation is assumed to take place from intraligand excited states localised on the azobenzene unit, the choice of the metal centre is known to drive the photochromic properties of the azobenzene unit 7a. 9 In fact, the photoisomerisation was reported to be suppressed in azobenzene‐containing polypyridine Ru II complexes, presumably due to an energy transfer from the reactive azobenzene‐localised intraligand (IL) state to low‐lying metal‐to‐ligand charge transfer (MLCT) states 9.…”

Induction of E/Z isomerization in a pendant metal-bound azobenzene: a synthetic, spectroscopic and theoretical study

“…[1][2][3][4] Azobenzene has been appended to a number of chromophores, including transition metal complexes, in an attempt to couple the E/Z isomerization process to an external electronic transition. [5][6][7][8][9][10][11][12][13] Transition metal compounds that exhibit metal to ligand charge transfer transitions (MLCT), as seen in many d 6 metal complexes, are ideal for transferring energy to an external group. [14][15][16][17][18] In this report, we present a study of two Re(CO) 3 diimine complexes with a pendant azobenzene group.…”