Impact of photosensitizer orientation on the distance dependent photocatalytic activity in zinc phthalocyanine–nanoporous gold hybrid systems

Abstract

The distance dependency of the photocatalytic activity in zinc phthalocyanine–nanoporous gold hybrid systems was investigated revealing the importance of photosensitizer orientation in novel hybrid-based photocatalysts.

Comparison of the photocatalytic activity of novel hybrid photocatalysts based on phthalocyanines, subphthalocyanines and porphyrins immobilized onto nanoporous gold

“…The photocatalytic singlet oxygen sensitization activity of the heterogeneous hybrid photocatalysts was determined by irradiation of the catalysts with a 300 W Xe arc lamp and a light intensity of 180 mW cm À2 within a self-built setup described elsewhere. 10,25 For the quantication of 1 O 2 formed during the catalyst run, DPF was used as chemical 1 O 2 quencher, allowing to follow the reaction progress via UV-Vis spectroscopy by the decrease of the DPF absorption band employing Lambert Beer's rule. DPF is structurally related to the standard chemical quencher 1,3-diphenylisobenzofuran (DPBF), reacting selectively with 1 O 2 via an endo-peroxide to a diketo species (Scheme 3).…”

“…The photocatalytic activity of the zinc(II) phthalocyanine (ZnPc) derivatives immobilized on various npAu supports had been investigated already in detail in the photooxidation of DPBF. 10,23,25 However, this class of hybrid material was also analyzed in the photooxidation of DPF, acting as reference system in comparison to the novel hybrid materials employing other macrocyclic metal complexes. For this purpose, two zinc(II) phthalocyanines containing either propynoxy-(1) or hexynoxy-(2) peripheral substituents were studied in the photooxidation reaction of DPF before and aer immobilized on a npAu powder support.…”

“…10,12,13 The orientation of the immobilized ZnPc derivatives on the npAu surface was shown to adopt a planar geometry due to the multidentate properties of the peripheral substituents enabling up to four binding sites to the azide groups of the SAM. 25 Due to the planar orientation, it was also shown that the central zinc ion forms an additional axial coordination to free azide groups of the SAM resulting in a penta-coordinated central ion known for various ZnPc and ZnTPP derivatives. [25][26][27][28][29][30][31][32] Within this orientation of the immobilized ZnPc, the axial coordination is stronger for the ZnPc derivative with shorter peripheral substituents, explaining the stronger observed increase in photocatalytic activity for the hybrid system H1 in comparison to H2.…”

“…B General procedure for the immobilization of the photosensitizers npAu powder was prepared employing a free corrosion technique and functionalization with an azide-terminated SAM was performed employing an ethanolic solution of 6-azidohexyl-1thioacetate as described previously by us. 10,25 The immobilization of the photosensitizers was achieved by subjecting the as prepared azide-functionalized npAu powder to a solution of Cu(MeCN) 4 PF 6 (931.8 mg, 2.5 mmmol), TBTA (1.326 mg, 2.5 mmol), hydroquinone (272.5 mg, 2.5 mmmol) and the respective photosensitizer (1-9, 0.15 mmol) dissolved in THF/H 2 O (5 mL, 3 : 1 v%). Aer a reaction time of 72 h, the reaction solution was discarded and the hybrid materials H1-H9 were repeatedly washed with THF to remove any unbound and physisorbed photosensitizer.…”

“…Photocatalytic oxidations were carried out in a self-built setup under irradiation with a 300 W Xe-arc lamp and a light intensity of 180 mW cm À2 , as described elsewhere. 10,25 In addition, a saturated aqueous mixture of NaNO 2 and NaNO 3 was used as lter solution for wavelength cutoff below 380 nm. For each photocatalytic experiment, the reaction vessel was lled with DMF (100 mL), the powder hybrid catalyst (25 mg) or the photocatalyst dissolved in DMF (100 mL, 0.1 nmol, molar ratio DPF/photosensitizer 30 000 : 1) was added and the setup was ushed with O 2 for 10 min to achieve gas saturation of the solvent.…”