Abstract
With a view to developing sensitizers for applications in photodynamic therapy (PDT), a series of quinaldine based squaraine dyes have been synthesized and the role of electronic factors in the dye formation have been investigated through absorption spectroscopy, product analysis and theoretical calculations. It has been observed that semisquaraine intermediates were formed as the sole products in the reaction of quinaldinium salts containing electron-donating substituents with squaric acid. However, with salts possessing electronegative and electron-withdrawing groups, the squaraine dyes were isolated in quantitative yields. The semisquaraine intermediates that have been isolated as the butyl adducts, could be converted to the squaraine dyes by reacting with the quinaldinium salts having electronegative and / or electron-withdrawing groups. These dyes exhibit absorption in the range 700-800 nm with significant molar extinction coefficients (e = 1-3 x 10 5 M -1 cm -1 ) and hence can have potential PDT applications.
Highlights
Photodynamic therapy (PDT) is an emerging modality for the diagnosis and treatment of cancer and related diseases.[1,2] photodynamic therapy (PDT) involves the inactivation of living cells by the combined action of light and a chemical
The reaction did not result in the formation of the corresponding squaraine dyes, instead, only butyl adducts of the semisquaraine intermediates 5b-c were isolated in 9095% yields
We have demonstrated that substitution on the benzene ring of the quinaldine moiety can affect the reaction between the quinaldinium salts and squaric acid resulting in the formation of the corresponding squaraine dyes
Summary
Photodynamic therapy (PDT) is an emerging modality for the diagnosis and treatment of cancer and related diseases.[1,2] PDT involves the inactivation of living cells by the combined action of light and a chemical (photosensitizer). The reaction of the quinaldinium salt 4d with squaric acid under analogous conditions gave the corresponding squaraine dye 6d in 85% yield through the intermediacy of the semisquaraine 5d.
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