Highly Efficient Singlet Oxygen Generation and High Oxidation Resistance Enhanced by Arsole-Polymer-Based Photosensitizer: Application as a Recyclable Photooxidation Catalyst

Abstract

Photosensitizers have attracted considerable attention in various fields such as organic synthesis and medical care. For the development of high-performance photosensitizers, highly efficient and persistent singlet oxygen generators ( 1 O 2 ) having a high oxidation tolerance are strongly required. This study presents a detailed investigation of dithieno[3,2-b:2′,3′d]arsole-fluorene copolymer for its 1 O 2 generation ability and application as a photooxidation catalyst in vital organic reactions. Photoirradiation of an air-saturated solution of the polymer generates 1 O 2 , which was detected by 1 O 2 scavengers such as dihydronaphthoquinone and diphenylisobenzofuran. The polymer photosensitizer was completely stable in the presence of the strong oxidant 1 O 2 . The photosensitizer showed the highest quantum yield of 1 O 2 generation (Φ = 0.54) in single-component main-chain type π-conjugated polymers. The quantum yield of the arsenicfree analogue of the polymerbithiophene-fluorene copolymerwas significantly lower (Φ = 0.14), suggesting that the heavy-atom effect of arsenic can improve the efficiency of intersystem crossing (ISC) from the singlet excited state to the triplet excited state of the photosensitizer. In addition, when utilized as a recyclable photocatalyst for the oxidation reaction, the photosensitizer exhibited excellent oxidation resistance without losing its recognizable catalytic activity. Finally, we demonstrated the release of 1 O 2 into the air by a film of the present polymer. Persistent 1 O 2 generation was observed on film irradiation without polymer decomposition. These results suggested that the polymer exhibited excellent oxidation resistance in solution as well as in the solid state. The present molecular design concept of the photosensitizer using the main group element can facilitate the development of further functional optical materials.

Penetration of Singlet Oxygen into Films with Oxygen Permeability Coefficient Close to that of Skin

“…Our data proved that 1 O 2 was able to move between the different polymer layers. This finding suggests the possibility of a new method for detecting 1 O 2 , which has mostly been detected in solution in the past (26)(27)(28)(29)41,42). When DPBF is incorporated into a solid film, it is less susceptible to fading than DPBF in solution when exposed to light.…”

New Approach in the Application of Conjugated Polymers: The Light-Activated Source of Versatile Singlet Oxygen Molecule

“…Next to highly porous systems, the 2D- and the linear 1D-conjugated polymers can be also used in light-activated wastewater treatments. The thin layers of electrochemically polymerized phenothiazines showed to be effective in the degradation of the phenol from the aqueous solution under visible light illumination [ 145 ], while the dithienoarsole-fluorene-based polymer [ 146 ] and 1D polyporphyrin-benzobisoxazole [ 147 ] were successfully applied as sources of singlet oxygen in the photodegradation of rhodamine-based dyes. Both CPs were active under visible-light irradiation, could be recycled, and showed high photocatalytic capabilities.…”

Synthesis, Structural Characterization, and Optical Properties of Benzene-Fused Tetracyclic and Pentacyclic Stiboles

“…For example, five-membered phospholes and their derivatives have been extensively studied as basic units of functional materials with luminescent, semiconducting, and sensing properties [2][3][4][5][6]. Arsoles, containing the homologous element, arsenic, have been reported as luminescent substances that are less likely to be oxidized than phospholes, although toxicity is a concern [7][8][9][10][11]. Antimony, another homologue located in the fifth period of group 15 elements in the periodic table, is expected to impart phosphorescence similarly to bismuth and tellurium based on the "heavy element effect", in contrast to lighter elements such as phosphorus [12][13][14][15][16].…”