Silica gel-supported photofunctional silicon phthalocyanine complexes: Photodesorption of molecular oxygen by singlet oxygen generation
Graphical abstract
Silica gel-supported phthalocyanine complexes exhibit the photodesorption of molecular oxygen due to singlet oxygen generation.
Introduction
The immobilization of functional molecules on a large area of silica (SiO2) is an important and useful approach to prepare functional self-assembled monolayers, sensors, catalysts, and stationary phases in high performance liquid chromatography [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. In particular, the photochemistry of molecules on SiO2 surfaces has attracted considerable attention from the viewpoint of understanding surfaces or preparing photofunctional materials, i.e., luminescence-based sensors and photocatalysts [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. However, photoadsorption or photodesorption has been investigated in only a few cases related to the photochemistry of molecules on SiO2 surfaces [16], while they have been well examined in the case of other inorganic materials [17], [18], [19], [20], [21], [22], [23], [24], [25].
In this study, we report the first example of the photodesorption of molecular oxygen from SiO2 using red light irradiation. Here, novel organic–inorganic hybrid materials – silica gel-supported photofunctional phthalocyanine (Pc) derivatives (Fig. 1) – have been prepared. This attractive phenomenon can be reasonably interpreted by the cooperative phenomenon between singlet oxygen (1Δg) generation by Pcs and oxygen desorption from SiO2.
Section snippets
Experimental
SiPc(OH)2 and SiNc(OH)2 (Fig. 1) were synthesized according to the previously reported methods [26], [27]. Silica gels (Wakogel 325 mesh and Wakosil 5SIL) were purchased from Wako Pure Chemical Industries, Ltd. A toluene solution (12 ml) containing SiPc(OH)2 (5 mg) and SiO2 (880 mg) was refluxed for 8 h after stirring it overnight [9], [10], [26]. After filtration and washing with CH2Cl2/MeOH (3:1 v/v), a negligibly small amount of SiPc(OH)2 (3%) was removed and SiPc–SiO2 was isolated. Since the OH
Results and discussion
The electronic absorption and fluorescence spectra of SiPc–SiO2 in CHCl3 are shown in Fig. 2. While the concentrations of SiPcs are very high (∼10−3 M estimated from the volume and the number of moles of SiPcs), SiPc–SiO2 shows a sharp Q absorption band and normal fluorescence lifetime comparable to those of SiPc(OH)2. These results indicate that SiPcs on silica gels exhibit monomeric photophysical properties even at very high concentrations and that silica gels are effective supports to
Conclusions
Due to the cooperative phenomenon between the singlet oxygen (1Δg) generation by SiPcs and the oxygen desorption from SiO2, the photodesorption of molecular oxygen by using red light irradiation was observed. To the best of our knowledge, this photodesorption of molecular oxygen from the SiO2 surfaces was observed for the first time, while the photoadsorption of oxygen in SiO2 irradiated with UV light (<250 nm) has been reported earlier [16]. In addition, SiPc–SiO2 is a promising material
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research (Category B No. 19350028), the Ito Science Foundation, and the COE project, Giant Molecules and Complex Systems, 2006 from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
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