Synthesis, Photophysics, and Switchable Luminescence Properties of a New Class of Ruthenium(II)–Terpyridine Complexes Containing Photoisomerizable Styrylbenzene Units

Abstract

We report here the synthesis and structural characterization of a new class of homoleptic terpyridine complexes of Ru(II) containing styrylbenzene moieties to improve room-temperature luminescence properties. Solid-state structure determination of 2 was done through single-crystal X-ray diffraction. Tuning of photophysical properties was done by incorporating both electron-donating and electron-withdrawing substituents in the ligand. The complexes exhibit strong emission having lifetimes in the range of 10.0–158.5 ns, dependent on the substituent and the solvent. Good correlations were also observed between Hammett σ p parameters with the lifetimes of the complexes. Styrylbenzene moieties in the complexes induce trans–trans to trans–cis isomerization accompanied by huge alteration of their spectral profiles upon treating with UV light. Reversal of trans–cis to trans–trans forms was also achieved on interacting with visible light. Change from trans–trans to the corresponding trans–cis form leads to emission quenching, whereas trans–cis to the corresponding trans–trans form leads to restoration of emission. In essence, “on–off” and “off–on” photoswitching of luminescence was observed. Calculations involving density functional theory (DFT) and time-dependent-DFT methods were performed to understand the electronic structures as well as for appropriate assignment of the absorption and emission bands.

Photocatalytic Hydrogen Evolution Driven by a Heteroleptic Ruthenium(II) Bis(terpyridine) Complex

“…In addition, the coordination geometry of the bis terpyridine complex allows the design of linear arrays or polymers, [12][13][14] whose properties can be tuned by using different spacers as well as substituents. [15][16][17] Despite intensive efforts dedicated to improving their photophysical properties, ruthenium bis tridentate complexes have, to the best of our knowledge, not been shown to photocatalyze hydrogen production. 18,19 Herein, we report a newly designed heteroleptic complex capable of coordinating to the catalyst via peripheral pyridine substituents and discuss its photophysical and electrochemical properties as well as its potential as photosensitizer in hydrogen production experiments.…”

Low-cost photo-switches based on stilbene-appended Zn(II)–terpyridine complexes

“…The terpyridine ligands (tpy-pvp-X with X = H, Me and NO 2 ) are synthesized upon reacting tpyPhCH 2 PPh 3 Br with 4-substituted benzaldehyde in DCM at ~ 5 °C and thoroughly characterized by adopting our reported procedure [30][31][32]. The Zn(II) complexes are synthesized upon treating tpy-pvp-X with [Zn(ClO 4 ) 2 ] in 2:1 molar ratio in chloroform-methanol (1:1, v/v) mixture at RT and purified through column chromatography followed by recrystallization from chloroform-methanol (1:2, v/v) mixture.…”

“…Nishihara's group reported some terpyridine complexes of Ru(II) and Rh(III) coupled with photoactive azo unit [68]. Recently, our group initiated the isomerization studies of stilbene-appended terpyridine complexes of Fe(II), Ru(II) and Os(II) metals [30,31,33,59]. Photoisomerization behaviors of various heavier transition metal complexes (Re, Co, Rh, Ir, etc.)…”

“…Even though lots of studies were performed with purely organic stilbene derivatives, but analogous studies with their coordination complexes are comparatively limited in the literature [18][19][20][21][22]. Compared to organic compounds, metal complexes offer a greater variety of electronic structures, in relation to the coordination sphere, electronic configuration and oxidation state of the metal [23][24][25][26][27][28][29][30][31][32][33]. To mimic the function of photochemical molecular devices (such as photo switches) in metal complexes, one of the most effective strategies is to reversibly alter their properties by inducing conformational changes on the photo-responsive component appended on the ligands.…”

“…To mimic the function of photochemical molecular devices (such as photo switches) in metal complexes, one of the most effective strategies is to reversibly alter their properties by inducing conformational changes on the photo-responsive component appended on the ligands. A majority of the studies to this end are primarily focused on noble metals which are very expensive and the synthetic procedures often demand very drastic conditions [23][24][25][26][27][28][29][30][31][32][33]. Our primary objective in this work is to design suitable basemetal complexes which could show off similar behavior and can lead to the construction of a new class of low-cost and easily synthesizable photo-switches.…”