Synthesis of meso-tetra-(4-sulfonatophenyl) porphyrin (TPPS₄) – CuInS/ZnS quantum dots conjugate as an improved photosensitizer

Abstract

Background

 Metal-free, water-soluble and highly stable meso-tetra-(4-sulfonatophenyl) porphyrin (TPPS₄) has been studied for their singlet oxygen quantum yield. However, TPPS₄ suffers from inherent shortcomings. To address these, TPPS₄ was conjugated to ternary copper indium sulphide/ zinc sulphide (CuInS₂/ZnS) quantum dots (QDs).

Purpose

 We herein report for the first time the synthesis of TPPS₄–CuInS/ZnS QDs conjugate as an improved photosensitizer.

Methods

 Water-soluble TPPS₄ was synthesized from tetraphenylporphyrin (TPPH₂) after silica-gel purification. The CuInS/ZnS QDs were synthesized by hydrothermal method at a Cu:In ratio of 1:4. The porphyrin–QDs conjugate was formed via the daggling sulfonyl bond of the porphyrin and amine bond of the QDs. The effect of pH on the optical properties of TPPS₄ was evaluated. The effect of Zn:Cu + In ratio on the ZnS shell passivation was examined to reduce structural defects on the as-synthesized QDs.

Results: 

Various spectroscopic techniques were used to confirm the successful conversion of the organic TPPH₂ to water-soluble TPPS₄. The singlet oxygen generation evaluation shows an improved singlet oxygen quantum yield from 0.19 for the porphyrin (TPPS₄) alone to 0.69 after conjugation (CuInS/ZnS-TPPS₄) with an increase in the reaction rate constant (k (s-1)).

Keywords:

• CuInS/ZnS
• meso-tetra-(4-sulfonatophenyl) porphyrin
• TTPS₄
• singlet oxygen
• conjugation
• quantum dots

Acknowledgment

The authors would like to thank the National Research Foundation (NRF), South Africa under the Competitive Programme for Rated Researchers (Grant no: 106060), Thuthuka (Grant no: 107295), equipment-related travel and training (Grant no 109892), Cape Peninsula University of Technology and the University of Johannesburg, South Africa, Faculty of Science Research Committee, and University research Committee, South Africa for financial support. OSO is also grateful to Tohoku University for the two month research visit under the Tohoku University Special Measure.

Disclosure

Ms Vuyelwa Ncapayi reports grants from National Research Council, during the conduct of the study. The authors report no other conflicts of interest in this work.