Stimuli-Responsive Near-Infrared Emissive Os(II)–Terpyridine Complexes with a Sense of Logic

Abstract

Two bis-tridentate Os(II) compounds based on a heteroditopic terpyridine–bipyridine-type ligand were synthesized, and their photophysical properties were thoroughly studied. The compounds exhibit strong spin-allowed 1 MLCT bands in the visible domain (489–521 nm) as well as weak 1 GS to 3 MLCT bands within the 668–815 nm domain. The compounds display strong luminescence from the 3 MLCT state in the near-infrared domain (728–780 nm) at room temperature having lifetimes in the range of 20.0–171.0 ns. After coordination of [Os(tpy-PhCH 3 /H 2 pbbzim) 2 ] 2+ unit to the terpyridine site of tpy-Hbzim-dipy, the complexes offer vacant pyridine–imidazole motifs for interacting with cationic and anionic guests. Consequently, photophysical properties of the compounds were tuned to a great extent upon interaction with selected cations, anions, pH, as well as protons. Anion-induced alteration of the ground- and excited-state properties of the compound lead to recognition of specific anions in solution. Significant change in the optical spectral behaviors as well as switching of emission spectral properties of the compounds was done in the NIR region upon treating with anions, cations, protons, and solvents (dichloromethane, acetonitrile, methanol, dimethylsulfoxide, and water). Moreover, the optical outputs in response to external stimuli were used to demonstrate binary functions of two-input IMPLICATION, NOR, and XNOR logic gates.

Emission Switching in the Near-Infrared by Reversible Trans–Cis Photoisomerization of Styrylbenzene-Conjugated Osmium Terpyridine Complexes

“…All complexes possess a reversible wave with E 1/2 in the range of 0.92−94 V due to Os II /Os III oxidation and a set of quasi-reversible and/or irreversible waves in the potential range of −1.0 to −2.3 V due to reductions of the tpy and nitrobenzene units. 56 A representative CV of 2 is displayed in Figure 3. Theoretical calculations also show that the spin density for the one-electron-oxidized form was found to be localized mainly on the osmium center and, to some extent, on the stilbene unit but on tpy motifs (except 4, where localization occurs on the nitrobenzene unit) in their one-electron-reduced form (Figure S15).…”

“…The results are summarized in Table . All complexes possess a reversible wave with E 1/2 in the range of 0.92–94 V due to Os II /Os III oxidation and a set of quasi-reversible and/or irreversible waves in the potential range of −1.0 to −2.3 V due to reductions of the tpy and nitrobenzene units . A representative CV of 2 is displayed in Figure .…”

“…Both electron-donating and -withdrawing substituents were incorporated in the tpy-pvp-X moiety to fine-tune their optical behaviors and also to alter the rate of photoisomerization. Although NIR-emitting osmium­(II) polypyridyl complexes are reported in our laboratory − and also by other research groups, − we found no such reports in which photoisomerization studies of osmium­(II) terpyridine complexes coupled with styrylbenzene units have been performed.…”