Sensitizing the Sensitizer: The Synthesis and Photophysical Study of Bodipy−Pt(II)(diimine)(dithiolate) Conjugates

Abstract

The dyads 3, 4, and 6, combining the Bodipy chromophore with a Pt(bpy)(bdt) (bpy = 2,2'-bipyridine, bdt = 1,2-benzenedithiolate, 3 and 6) or a Pt(bpy)(mnt) (mnt = maleonitriledithiolate, 4) moiety, have been synthesized and studied by UV-vis steady-state absorption, transient absorption, and emission spectroscopies and cyclic voltammetry. Comparison of the absorption spectra and cyclic voltammograms of dyads 3, 4, and 6 and those of their model compounds 1a, 2, 5, and 7 shows that the spectroscopic and electrochemical properties of the dyads are essentially the sum of their constituent chromophores, indicating negligible interaction of the constituent chromophores in the ground state. However, emission studies on 3 and 6 show a complete absence of both Bodipy-based fluorescence and the characteristic luminescence of the Pt(bpy)(bdt) unit. Dyad 4 shows a weak Pt(mnt)-based emission. Transient absorption studies show that excitation of the dyads into the Bodipy-based (1)ππ* excited state is followed by singlet energy transfer (SEnT) to the Pt(dithiolate)-based (1)MMLL'CT (mixed metal-ligand to ligand charge transfer) excited state (τ(SEnT)(3) = 0.6 ps, τ(SEnT)(4) = 0.5 ps, and τ(SEnT)(6) = 1.6 ps), which undergoes rapid intersystem crossing to the (3)MMLL'CT state due to the heavy Pt(II) ion. The (3)MMLL'CT state is then depopulated by triplet energy transfer (TEnT) to the low-lying Bodipy-based (3)ππ* excited state (τ(SEnT)(3) = 8.2 ps, τ(SEnT)(4) = 5 ps, and τ(SEnT)(6) = 160 ps). The transition assignments are supported by TD-DFT calculations. Both energy-transfer processes are shown to proceed via a Dexter electron exchange mechanism. The much longer time constants for dyad 6 relative to 3 are attributed to the significantly poorer coupling and resonance of charge-separated species that are intermediates in the electron exchange process.

Light-driven generation of hydrogen: New chromophore dyads for increased activity based on Bodipy dye and Pt(diimine)(dithiolate) complexes

“…The dithiolene ligand precursor that led to formation of dyad 4 with R=H [that is, 2-oxobenzo[d] [1,3]dithiole-5-[1,3,5,7-tetramethyl-2,6-diethyl(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene)] (Bodipy-bdtCO)] was prepared following the previously reported procedure involving the compound denoted as (OHC)-bdtCO (51). Dyads 4 with R = COOMe, P(O)(OEt) 2 , CH 2 (P(O)(OEt) 2 ) were synthesized according to Scheme 2.…”

Photophysics of BODIPY Dyes as Readily-Designable Photosensitisers in Light-Driven Proton Reduction

“…Further evidence for the important role of a triplet excited state was reported by the groups of Weare and Luo for intermolecular [16], as well as intramolecular [13,[15][16][17] BODIPY-cobaloxime systems. More recently, Eisenberg et al have used a combination of strongly light-absorbing BODIPYs and platinum diamine dithiolate charge transfer chromophores for sensitizing TiO2 in light-driven reduction of aqueous protons [18,19]. A survey of the combined influence of BODIPY halogenation and introduction of sterically-demanding aryl groups on photocatalytic hydrogen production activity was presented by the same authors, showing the presence of a pronounced heavy atom effect as well as an enhanced dye stability with an increase in steric demand at the meso position [20].…”

Photo-induced redox catalysis for proton reduction to hydrogen with homogeneous molecular systems using rhodium-based catalysts

“…Many linked systems have been reported in literature that combine a Ru, Ir, Re, or Os complex, a porphyrin (Zn, Mg, Al), or an organic dye as the PS with a Pt, Pd, Rh, Co or Fe complex as H 2 -evolving catalyst [11,[27][28][29][30][31][32][33][34][60][61][62][63][64][65][66][67][68][69][70]. In association with a sacrificial electron donor, most of them operate in organic medium or in a mixture of aqueous-organic solvents, and only a few have been reported to be active in fully aqueous solution [40,62,[70][71][72]. Some of these linked systems have provided high turnover numbers per catalyst (or photocatalyst) [68] and the most active linked systems so far in water relies on rhodium-based catalyst [72].…”