Absorption Spectra, Photophysical Properties, and Redox Behavior of Ruthenium(II) Polypyridine Complexes Containing Accessory Dipyrromethene−BF₂Chromophores

Abstract

The six multichromophoric species 1-6, containing the potentially luminescent Ru(II) polypyridine subunits and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene fluorophores (dipyrromethene-BF(2) dyes, herein after called bodipy), have been prepared and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox properties have been investigated (for the structuralformulas of all the compounds, see Figure 1). For comparison purposes, also the same properties of the bodipy-based free ligands have been examined. Three of the multichromophoric species (1-3) are based on the Ru(bpy)(3)-type metal subunit, whereas 4-6 are based on the Ru(terpy)(2)-type metal subunit. Transient absorption spectroscopy at room temperature of all the compounds has also been performed. The absorption spectra of all the metal complexes show features that can be assigned to the Ru(II) polypyridine subunits and to the bodipy centers. In particular, the lowest energy spin-allowed pi-pi* transition of the bodipy groups dominates the visible region, peaking at about 530 nm. All the new complexes exhibit a rich redox behavior, with reversible processes attributed to specific sites, indicating a small perturbation of each redox center and therefore highlighting the supramolecular nature of the multichromophoric assemblies. Despite the good luminescence properties of the separated components, 1-6 do not exhibit any luminescence at room temperature; however, transient absorption spectroscopy evidences that for all of them a long-lived (microsecond time scale) excited state is formed, which is identified as the bodipy-based triplet state. Pump-probe transient absorption spectroscopy suggests that such a triplet state is formed from the promptly prepared bodipy-based (1)pi-pi* state in most cases by the intervention of a charge-separated level. At 77 K, all the complexes except complex 1 exhibit the bodipy-based fluorescence, although with a slightly shortened lifetime compared to the corresponding free ligand(s), and 4-6 also exhibit a phosphorescence assigned to the bodipy subunits. Phosphorescence of bodipy species had never been reported in the literature to the best of our knowledge: in the present cases we propose that it is an effective decay process thanks to the presence of the ruthenium heavy atom and of the closely lying (3)MLCT state of the Ru(terpy)(2)-type subunits.

Bodipy-ruthenium(II) tris-bipyridyl dyads for homogeneous photochemical oxidations

“…Their molecular structures were unambiguously assigned by using 1 H, 13 C, 19 F and 11 B NMR spectroscopy, electrospray mass spectrometry and elemental analysis. Both dyads analysed by ESI-MS gave an intense molecular peak with the expected isotopic profile corresponding to the loss of two PF 6 -counter anions assigned to a doubly charged species.…”

“…The oxidation peak at +1.09 V is assigned to the formation of a Bodipy + (BD + ) unit; the irreversibility is also known for other polypyridyl-containing Bodipy molecules. 12,13 The quasireversible wave seen at -1.15 V is associated with the addition of one electron to the Bodipy site.…”

Synthesis, Characterization, and Photophysical Studies of Some Novel Ruthenium(II) Polypyridine Complexes Derived from Benzothiazolyl hydrazones

“…The other absorption bands of the ligands are due to various - * and - * transitions [5,14,27,29]. In the UV-vis absorption spectra of complexes and the bands at 322, 332, and 323 nm should receive a dominant contribution from transition involving the ligands 3a, 3d, 3e, respectively [6,14,28]. In particular, the bands with 290-300 nm range should receive a dominant contribution from - * transition involving bpy and phen moieties [7,[31][32][33].…”

“…The polypyridine complexes of Ru(II) have been studied extensively with the point of interest being their rich and well characterized photophysics [6,7]. In recent years, transition metal complexes have been used extensively in the fore front of fields such as probes of DNA structure, DNAdependent electron transfer, and site-specific DNA cleavage [8][9][10].…”

Fluorescent poly(boron enaminoketonate)s: synthesis via the direct modification of polyisoxazoles obtained from the click polymerization of a homoditopic nitrile N-oxide and diynes

“…[1][2][3][4] The optical properties of boron diketonate such as its large Stokes shift and two-photon absorption cross sections and the versatile applications based on the incorporation to various organic backbones provide its potential usefulness for a molecular probe, 5 laser, 6 and optical sensing applications. 7,8 Research by Fraser et al on the applications to polymeric materials has reported synthesis of boron diketonate-containing polylactide and the oxygen-sensing property. 9 Moreover, Chujo et al have demonstrated synthesis and emission color-tunings of the main chain-type poly(boron diketonate)s. [10][11][12] However, the synthetic difficulty of the boron diketonate-containing polymers restricts applicability of the polymer.…”