Enhancing Singlet Oxygen Generation in Conjugates of Silicon Nanocrystals and Organic Photosensitizers

Abstract

Silicon nanocrystals (SiNCs) are regarded as a green and environmentally friendly material when compared with other semiconductor nanocrystals. Ultra-small SiNCs (with the size 4.6-5.2 nm) demonstrate strong UV absorption and photoluminescence in the near infrared (NIR) range with the high photoluminescence quantum yield (PLQY) up to 60%. In contrast to nanoporous silicon, ultra-small SiNCs do not possess an intrinsic ability to generate singlet oxygen (1 O 2). However, we demonstrate that SiNC-dye conjugates synthesized via microwave assistant hydrosilylation reaction produce 1 O 2 with moderate quantum yield () up to 27% in cyclohexane. These interesting results were obtained via measurements of singlet oxygen phosphorescence at 1,270 nm. SiNCs play an important role in the production of singlet oxygen as SiNCs harvest UV and blue radiation and transfer absorbed energy to a triplet state of the attached dyes. It increases the population of the triplet states and leads to the enhancement of the singlet oxygen generation. Simultaneously, the SiNC-dye conjugates demonstrate NIR luminescence with the PLQY up to 22%. Thus, the luminescence behavior and photosensitizing properties of the SiNC-dye conjugates can attract interest as a new multifunctional platform in the field of bio-applications.

Thermal Disproportionation for the Synthesis of Silicon Nanocrystals and Their Photoluminescent Properties

“…To further enhance the singlet oxygen generation of SiNCs, the SiNC-dye conjugates were investigated. The SiNCs absorbed near-UV radiation and then transferred this energy to the triplet state of the attached dyes, which increased the number of triplet states and finally enhanced the singlet oxygen generation (Beri et al, 2020). As a reactive oxidant, singlet oxygen exhibited great potential for quantities of applications, such as chemical synthesis (Manfrin et al, 2019;Karsili andMarchetti, 2020), environmental protection (García-Fresnadillo, 2018;Bu et al, 2021), and photodynamic therapy (Guo et al, 2010; Bartusik-Aebisher Osuchowski et al, 2021), and thus the application fields of SiNCs were also broadened.…”

Silicon quantum dots: surface matter, what next?

“…The synthesis methods used in the charting are also diverse, such as plasma synthesis, 7,[18][19][20][21][22][23][24][25][26] Tilley method with silicon-rich precursors, 27,28 disproportionation reactions of silicon-rich precursors (e.g., SiO, HSQ, and TES) 4,6,11,12,15,17, followed by chemical etching, electrochemical synthesis, electrodeposition, chemical vapor deposition, and physical vapor deposition. Hydrosilylation reactions may vary, e.g., by thermal reactions in microwave reactors, [53][54][55]68,69 organometallic catalysts, and radical initiator reactions. 29,31,48,51 It is worth noting that there are no differentiated R-SiQDs based on Fig.…”

“…Contrary to our previous discussion, it turns out that the PLQY measurements deviate from quantum confinement theory for the ligands that are not derived from alkyl groups. 37,[76][77][78] Reports from various authors 9,27,28,[53][54][55]62,74,[79][80][81] indicate that the attachment of more electronegative ligands causes a shift in the emission of SiQDs. 82 For example, SiQDs attached to carbazole (Ca) shows a blue emission shift from l max 780 nm for an average f 3.0 nm diameter of R-SiQDs to l max 530 nm.…”

“…The synthesis methods used in the charting are also diverse, such as plasma synthesis, 7,18–26 Tilley method with silicon-rich precursors, 27,28 disproportionation reactions of silicon-rich precursors ( e.g. , SiO, HSQ, and TES) 4,6,11,12,15,17,29–70 followed by chemical etching, electrochemical synthesis, electrodeposition, chemical vapor deposition, and physical vapor deposition. Hydrosilylation reactions may vary, e.g.…”

“…Hydrosilylation reactions may vary, e.g. , by thermal reactions in microwave reactors, 53–55,68,69 organometallic catalysts, and radical initiator reactions. 29,31,48,51 It is worth noting that there are no differentiated R-SiQDs based on alkyl chain length, precursors, and reaction methods to design Fig.…”