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

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)).