Ftalosiyanin-kuantum dot konjugatların eldesi ve elektrokimyasal uygulamaları
Phthalocyanine and heteroatom‐doped carbon quantum dots conjugate: synthesis and electrochemical investigation
Yazar: BAŞAK GİZEM KARAHAN
Danışman: PROF. DR. İBRAHİM ÖZÇEŞMECİ
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Kimya Ana Bilim Dalı / Kimya Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Kimya = Chemistry

Özet:
Karbon bazlı kuantum noktalarının tetrapirol bileşikleri (porfirin ve ftalosiyanin gibi) ile birleştirilmesi, bileşenlerinden üstün özelliklere sahip moleküler nano mimariler elde etmek için çok önemlidir. Kuantum nokta/ftalosiyanin (QD/Pc) hibrit sisteminin konjugasyonu, manyetik özellikler, elektronik seviye hizalaması, yük aktarımı ve substrat bağlanmasındaki değişikliklerle çeşitli senkronize adsorpsiyon konformasyonlarını elde etmek için yeni fırsatlar sağlamaktadır. Farklı türdeki QD/Pc konjugatlarının sentezi, biyomimetik sistemlerde, biyolojik uygulamalarda ve katalitik proseslerde ayarlanmış işlevsellik avantajıyla benzersiz optik, geometrik ve elektronik özellikler oluşturmak için özelleştirilmiş moleküller arası ilişkiler de sunabilir.

Bu tez çalışması kapsamında, tetra-hidroksitiyoetil terminal grupları sübstitüe edilmiş metalsiz ve kobalt (II) ftalosiyaninler, QD/Pc nanokonjugatlarını oluşturmak üzere karbon kuantum nokta (CQD) ve bor katkılı karbon kuantum noktasına (CBQD) kovalent olmayan bir şekilde (elektrostatik ve/veya π-π etkileşimiyle) bağlanmıştır. QD/Pc konjugatları farklı spektroskopik teknikler (FT-IR, UV-Vis, XRD, Raman ve AFM) kullanılarak karakterize edilmiştir. Sentez sonrası ilk aşamada, QD/Pc konjugatlarının elektrokimyasal performansları, karbon ve bor içeren QD'lerin H2Pc ve CoPc'nin redoks mekanizması üzerindeki etkisini belirlemek için döngüsel voltametri (CV) kullanılarak araştırılmıştır. Bu aşamadan sonra, asidik ortamlarda QD/Pc konjugatların katalizör olarak kullanıldığı elektrokimyasal hidrojen oluşum reaksiyonu (HER) üzerine bir araştırma yürütülmüştür. Elde edilen sonuçlara göre, CBQD/CoPc konjugat sistemi, asidik koşullarda üstün hidrojen oluşum reaksiyonu (HER) performansı sergilemiştir.

Abstract:
Phthalocyanines (Pc) are planar macrocyclic compounds with an 18 π-electron system, formed by the condensation of four iminoisoindoline units. They have strong physical, chemical, and electronic properties thanks to the delocalized electrons in their structure. Due to their stable structure and potential optical properties, they can be used in many chemical and biological fields.

Phthalocyanines (Pcs) have numerous scientific and technological applications, often involving surface/interface-related properties due to their size, remarkable stability, tunable ligand functionality, and planar nature of the main macrocyclic core [1]. The planar structure of phthalocyanine compounds is beneficial for adsorption via significant van der Waals interactions, bringing other atoms closer to the phthalocyanine core. Phthalocyanines have distinctive photophysical properties. They show two strong absorption regions, one in the UV region at around 300-400 nm (B band) and the other in the visible part of the spectrum around 600-700 nm (Q band), and an enormous extinction coefficient. These properties make phthalocyanines valuable in the formation of functional nanostructures with donor-acceptor arrangements for applications such as photocatalysis, solar energy conversion, photodynamic therapy (PDT), molecular electronics, and so on [2-4]. 

In recent years, obtaining new phthalocyanine-based materials is particularly important to respond to advanced technology applications. To meet this need,phthalocyanine compounds have been used in many high-tech applications such as solar cells, nanobiotechnology, biosensors, photodynamic therapy for cancer treatment, and other medical applications. 

Quantum dots (QDs) are fluorescent, semiconductor nanocrystals with diameters ranging from 2-10 nm. Due to their photophysical properties such as high quantum yield, narrow emission band, and stability, they have been the center of interest in many fields such as bioimaging, LED, optoelectronic device technology, and solar panels. Quantum dots are usually synthesized as nanocrystalline forms of heavy metal chalcogenides such as CdS, CdSe, and PbS. These types of quantum dots have limited applications due to the toxic effects of heavy metals in their structures. However, in the early 2000s, heavy metal-free and environmentally friendly carbon-based quantum dots were developed.

Carbon-based quantum dots (CQDs) possess both two-dimensional (2D) fascinating properties and the extraordinary physicochemical properties of quantum dots, namely the quantum confinement effect [5]. CQDs have been extensively investigated due to their desirable properties such as easy synthesis, low cost, non-toxicity, eco-friendly synthesis, controllable chemical functionality, good biocompatibility, high stability, and stable photoluminescence [6]. These properties, together with their large surface areas and abundant functional groups (e.g., hydroxyl, amino, and carboxyl), provide enormous potential applications in areas such as electronics, optics, biomedicine, and energy [7,8]. In particular, doping CQDs with boron atoms effectively regulates the electronic and optical properties of CQDs. The empty p-orbital of the B atom can be effectively conjugated with C=C atoms, which can reduce the distance between B3+ and the sp2 clusters of CBQDs. This change can enhance the electronic delocalization in the carbon matrix of the quantum dot [9]. 

Combining carbon-based quantum dots with tetrapyrrole compounds (such asporphyrin and phthalocyanine) is crucial to obtain molecular nanoarchitectures with superior properties from their constituents. Conjugation of the quantum dot/phthalocyanine (QD/Pc) hybrid system provides new opportunities to obtain various synchronous adsorption conformations with changes in magnetic properties, electronic level alignment, charge transfer, and substrate binding. The synthesis of different types of QD/Pc conjugates can also offer customized intermolecular relationships to generate unique optical, geometric, and electronic properties in biomimetic systems, biological applications, and catalytic processes with the advantage of tuned functionality.

Different carbon nanomaterials regularly integrated into tetrapyrrole compounds [29] are crucial for obtaining compounds that mimic various vital processes by forming conjugates [30-34]. The analysis of new carbon forms [35,36] has changed the horizon of nanostructures and opened new avenues for different discoveries in this field [20,37,38]. QDs with a unique structure have become a focus due to their great potential in various applications [39-45]. QDs are zero-dimensional, sp2 -hybridized, fluorescent, semiconducting, carbon nanocrystals (typical size range 3-30 nm). Their zero dimensions are arranged in a honeycomb structure with carbon lattices and assembled via functional chemical groups on the edge/surface [36,46-49]. Interactions in the QD/Pc hybrid system [50] provide new opportunities to achieve various synchronized adsorption conformations with a change in substrate binding, electronic level alignment, charge transfer [39], axial/peripheral ligation (chemical), and magnetic properties [25,51,52]. In the pursuit of new applications, the advantage of systematically tuned functionalization of QD/Pc hybrid systems also offers tuned intermolecular relationships for the generation of unique optical, geometrical, and electronic properties in biomimetic systems [39,53,54]. Therefore, phthalocyanine- based QD nanohybrids show structure-function relationships depending on kinetics, environment, and other factors. Nowadays, theoretical modeling including principal component analysis (PCA) can rapidly reveal the distinctive signatures of responses from nanohybrid systems and their components [25,55]. Undoubtedly, the emergence of pragmatically designed, bio-inspired, semi-synthetic QD/Pc hybrid system derivatives will have a broad impact in the medical [56] therapeutic field, including drug development. Especially in PDT [57], optical properties and photosensitization [58] can be enhanced to improve its efficacy with domain-specific properties by reducing dose-limit side effects [39,46,47,51,59,60].

With their superior optical properties, they are frequently used together with phthalocyanines in energy applications, especially in the formation of quantum dot-phthalocyanine conjugate systems. An important advantage of quantum dot- phthalocyanine conjugate systems is that they can be easily synthesized. Macrocyclic rings containing suitable functional groups can spontaneously form nanoconjugate complexes in solutions with quantum dot structures. However, there is no study in the literature to obtain boron (B) atom-doped CQD/phthalocyanine conjugates and to investigate the photophysical and electrochemical properties of these structures. For this purpose, this thesis aims to synthesize QD/Pc (metal-free and cobalt (II)) conjugate structures containing carbon and carbon/boron atoms and to investigate their electrochemical properties for various energy applications. It is also aimed to investigate the effects of the synthesized QD/Pc conjugates on the electrochemical hydrogen evolution reaction (HER) using them as catalysts.

In this thesis, metal-free and cobalt (II) phthalocyanines with substituted tetra- hydroxythioethyl terminal groups were non-covalently (electrostatic and/or π–π interaction) linked to carbon quantum dot (CQD) and boron-doped carbon quantum dot (CBQD) to form QD/Pc nanoconjugates. The QD/Pc conjugates were characterized using different spectroscopic techniques (FT-IR, UV-Vis, XRD, Raman, and AFM). After the synthesis step, the electrochemical performances of the QD/Pc conjugates were investigated using cyclic voltammetry (CV) to determine the effect of carbon- and boron-containing QDs on the redox mechanism of H2Pc and CoPc. After this stage, a study was conducted on the electrochemical hydrogen evolution reaction (HER) in which QD/Pc conjugates were used as catalysts in acidic environments. According to the results obtained, the CBQD/CoPc conjugate system exhibited superior hydrogen evolution reaction (HER) performance in acidic conditions.