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## (Synthesis Example 6) Synthesis of 9-( 4-methacry› loxypheny 1 )dibenzothiophenium-benzoate ( Com› pound A3) 

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5.9 g of 9-(4-methacryloxyphenyl)dibenzothiophenium› benzoate (CompoundA3) is obtained in the same procedure as Synthesis Example 3 except that 9-(4-hydroxyphenyl) dibenzothiophenium-benzoate is used instead of 9-(4-hy› droxyphenyl)dibenzothiophenium-trifluoromethanesul- 60 fonate, methacrylic anhydride is used instead of methacryloyl chloride, and the concentrated organic layer is 65 purified by colunm chromatography (methylene chloride/ methanol=70/30 (volume ratio)). 

## <Synthesis of Compound A4 constituting Unit A> 

## (Synthesis Example 7) Synthesis of 9-( 4-methacry› loxyphenyl)dibenzothiophenium-hexafluoroanti› monate (Compound A4) 

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3.0 g of 9-( 4-methacryloxyphenyl)dibenzothiophenium› benzoate obtained in Synthesis Example 6 is dissolved in 24 g of methylene chloride, 1.5 g of potassium hexafluoroan- timonate and 24 g of pure water are added thereto, and the mixture is stirred at room temperature for 15 hours. There- after, phase separation is performed and the combined organic layer is washed with 24 g of pure water. The combined organic layer is concentrated and purified by colunm chromatography (methylene chloride/methanol=S0/ 20 (volume ratio)) to obtain 2.1 g of 9-( 4-methacryloxyphe› nyl )dibenzothiophenium-hexafluoroantimonate ( Compound A4). 

