The relationship between the boron dipyrromethene (BODIPY) structure and the effectiveness of homogeneous and heterogeneous solar hydrogen-generating systems as well as DSSCs

Abstract

A series of boron dipyrromethene (BODIPY) dyes (B1–B5) having H atoms at 2,6-positions or heavy-atom I at 2-/2,6-positions, and an ortho- or a para-COOH substituted phenyl moiety at the 8-position on the BODIPY core were synthesized and characterized. These organic dyes were applied for investigating the relationship between the BODIPY structure and the effectiveness of homogeneous and heterogeneous visible-light-driven hydrogen production as well as dye-sensitized solar cells (DSSCs). For the homogeneous photocatalytic hydrogen production systems with a cobaloxime catalyst, the efficiency of hydrogen production could be tuned by substituting with heavy atoms and varying carboxyl group orientations of BODIPYs. As a result, B5 containing two I atoms and an ortho-COOH anchoring group was the most active one (TONs = 197). The activity of hydrogen generation followed the order B5 > B3 > B2 > B1 = B4 = 0. An interesting “ortho-position effect” was observed in the present homogeneous systems, i.e., substitution groups were located at the ortho-position and higher hydrogen production activities were obtained. For the heterogeneous hydrogen production systems with a platinized TiO2 catalyst, the effectiveness of hydrogen evolution was highly influenced by the intersystem crossing efficiency, molar absorptivity and positions of the anchoring group of dyes. Thus, B3 having two core iodine atoms and a para-COOH group with TONs of 70 excelled other BODIPYs and the TONs of hydrogen generation showed the trend of B3 > B5 > B2 > B1 = B4 = 0. The results demonstrate that the present photocatalytic H2 production proceeds with higher efficiency and stability in the homogeneity than in the heterogeneity. In the case of DSSCs, the overall cell performance of BODIPY chromophores was highly dependent on both the absence or the presence of iodine atoms on the BODIPY core and –COOH anchoring positions. The B1–TiO2 system showed the best cell performance, because the most effective surface binding mode is allowed with this structure. This is also in contrast with the case of dye-sensitized solar H2 generation, in which B3 was the most efficient chromophore. The differences between dye-sensitized hydrogen-generating systems and DSSCs may be due to rates of electron transfer and the dye aggregation tendency.

Efficient Bimolecular Mechanism of Photochemical Hydrogen Production Using Halogenated Boron-Dipyrromethene (Bodipy) Dyes and a Bis(dimethylglyoxime) Cobalt(III) Complex

“…5 Note that, during preparation of this manuscript, Luo et al published a paper exploring the efficacy of COOH substituted phenyl groups on the Bodipy chromophore. 18 Luo's bimolecular system is also run at a very high chromophore concentration but has TONs of 200, lower than our values presumably due to the large concentration of dye. Perspective on systems containing unlinked components relative to those having tethered catalyst--chromophore dyads.…”

“…The systems were found to be effective for the light--driven generation of H 2 only when the Bodipy dye contains bromine or iodine substituents, indicating the importance of accessing the long-lived 3 ππ* state of the dye for photoinduced electron transfer. 14,15 Studies indicate that a free cobaloxime catalyst does not quench the fluorescence of the Bodipy, 18 but that a cobaloxime linked through the pyridine will, although it will not go on to produce hydrogen without the presence of a halogenated Bodipy. 14 Much discussion in the literature has centered on the effectiveness of chromophore - catalyst dyad constructs.…”

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

“…This suggests the necessity of a strong intersystem crossing (ISC) to form a long-lived, high-yield triplet excited state for efficient photocatalysis. 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].…”

“…Recent developments include the implementation of non-noble metal components, or even metal-free compounds into these systems and several groups described the use of classical organic dyes, such as Fluorescein, dyes, such as Fluorescein, porphyrins, or Eosin Y, as photosensitizer species [4][5][6][7][8][9][10][11]. Moreover, in recent years, BODIPY (boron dipyrromethene; IUPAC name: 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes have also attracted considerable attention as light-harvesting units in inter- [12] and intramolecular [13][14][15][16][17] photocatalyst systems for light-driven proton reduction. In a study of dye-sensitised TiO2/Pt systems, Eisenberg and McCamant showed that incorporation of heavy atoms such as bromine or iodine at the 2,6 position of the BODIPY results in a pronounced coupling between singlet and triplet states that greatly decreases fluorescence quantum yield and fluorescence lifetime compared to the parent halogen-free compound and results in a more active photosensitizer [12].…”

Orthogonal Supramolecular Assembly Triggered by Inclusion and Exclusion Interactions with Cucurbit[7]uril for Photocatalytic H2 Evolution

“…Photocatalytic H 2 evolution from water is afeasible strategy for solar energy conversion. [1][2][3] In general, am ulticomponent photocatalytic system forh omogeneous H 2 evolution is made up of the following three essential components: light-harvesting photosensitizer,H 2 -evolving catalyst, and sacrificiale lectron donor.C obaloximec ompounds, when coupled with various photosensitizers, such as [Ru(bpy) 3 ] 2 + , [4] Pt-acetylidec omplexes, [5] Re complexes, [6] and organic dyes, [7][8][9][10] have been applied as efficient catalystsf or photocatalytic H 2 evolution. To overcomet he diffusional constraints in dispersed system, supramolecular assemblies for photocatalytic H 2 evolution have been developedb yc ovalently linking cobaloxime and a photosensitizer.…”