Synthesis and photophysical and electrochemical properties of functionalized mono-, bis-, and trisanthracenyl bridged Ru(II) bis(2,2':6',2"-terpyridine) charge transfer complexes

Abstract

With the aim of developing new molecular devices having long-range electron transfer in artificial systems and as photosensitizers, a series of homoleptic ruthenium(II) bisterpyridine complexes bearing one to three anthracenyl units sandwiched between terpyridine and 2-methyl-2-butenoic acid group are synthesized and characterized. The complexes formulated as bis-4'-(9-monoanthracenyl-10-(2-methyl-2-butenoic acid) terpyridyl) ruthenium(II) bis(hexafluorophosphate) (RBT1), bis-4'-(9-dianthracenyl-10-(2-methyl-2-butenoic acid) terpyridyl) ruthenium(II) bis(hexafluorophosphate) (RBT2), and bis-4'-(9-trianthracenyl-10-(2-methyl-2-butenoic acid) terpyridyl) ruthenium(II) bis(hexafluorophosphate) (RBT3) were characterized by elemental analysis, FT-IR, UV-Vis, photoluminescence, (1)H and (13)C NMR spectroscopy, and electrochemical techniques by elemental analysis, FT-IR, UV-Vis, photoluminescence, (1)H and (13)C NMR spectroscopy, and electrochemical techniques. The cyclic voltammograms (CVs) of (RBT1), (RBT2), and (RBT3) display reversible one-electron oxidation processes at E 1/2 = 1.13 V, 0.71 V, and 0.99 V, respectively (versus Ag/AgCl). Based on a general linear correlation between increase in the length of π-conjugation bond and the molar extinction coefficients, the Ru(II) bisterpyridyl complexes show characteristic broad and intense metal-to-ligand charge transfer (MLCT) band absorption transitions between 480-600 nm, ε = 9.45 × 10(3) M(-1) cm(-1), and appreciable photoluminescence spanning the visible region.

Scheme 1

General reaction scheme for preparation of novel Ru(II) bis(terpyridyl-oligo-anthracene) bis(hexafluorophosphate) complexes.

Figure 1

UV-Vis absorption spectra of the (RBT1, RBT2, and RBT3) complexes at a concentration of 0.001 g/dm⁻³ in (CH₃Cl/MeOH, 1 : 1, v/v).

Figure 2

Emission spectra of the RBT1 (red), RBT2 (green), and RBT3 (purple) complexes at a concentration of 0.001 g/dm⁻³ in (CH₃Cl/MeOH, 1 : 1, v/v).

Figure 3

Cyclic and square wave voltammetry profiles of 1 × 10⁻³ M of RBT1 in freshly distilled DMF containing 0.1 M TBABF₄ supporting electrolyte. Step potential: 5 mV, amplitude: 50 mV versus Ag|AgCl, frequency: 10 Hz. Scan rate: 100 m Vs⁻¹ versus Ag|AgCl.

Figure 4

Cyclic and square wave voltammetry profiles of 1 × 10⁻³ M of RBT2 complex in freshly distilled DMF containing 0.1 M TBABF₄ supporting electrolyte. Step potential: 5 mV, amplitude: 50 mV versus Ag|AgCl, and frequency: 10 Hz. Scan rate: 100 m Vs⁻¹ versus Ag|AgCl.

Figure 5

Cyclic and square wave voltammetry profiles of 1 × 10⁻³ M of RBT3 complex in freshly distilled DMF containing 0.1 M TBABF₄ supporting electrolyte. Step potential: 5 mV, amplitude: 50 mV versus Ag|AgCl, frequency: 10 Hz. Scan rate: 100 m Vs⁻¹ versus Ag|AgCl.