Highly Efficient Singlet Oxygen Generation and High
Oxidation Resistance Enhanced by Arsole-Polymer-Based Photosensitizer:
Application as a Recyclable Photooxidation Catalyst
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 (1O2) 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 1O2 generation ability and application as a photooxidation catalyst
in vital organic reactions. Photoirradiation of an air-saturated solution
of the polymer generates 1O2, which was detected
by 1O2 scavengers such as dihydronaphthoquinone
and diphenylisobenzofuran. The polymer photosensitizer was completely
stable in the presence of the strong oxidant 1O2. The photosensitizer showed the highest quantum yield of 1O2 generation (Φ = 0.54) in single-component main-chain
type π-conjugated polymers. The quantum yield of the arsenic-free
analogue of the polymerbithiophene-fluorene copolymerwas
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 1O2 into the air by a film of the present polymer. Persistent 1O2 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.