Functional alkynyl-linked mono and double-decker metal phthalocyanines for multi-disciplinary biological and photoconductive applications

Abstract

Phthalocyanines (Pcs) and their metal correlatives (MPcs) have attained great significance lately because of the unique, planar and stable structural arrangement, optical, electronic and catalytic aspects they hold. Traditionally, phthalocyanine macrocycles were demanded as pigments and dyestuff, but they have found wide usage in different scientific and technological fields such as catalysis, liquid crystals, chemical sensors, photodynamic therapy, solar energy conversion, phototransistor, OFET and various biological applications in recent times. High redox character of metal phthalocyanines (MPcs) is a principal behind their extraordinary performance for these functions. All these features can be altered simply by modifying metal centers or side chains. More recently, much research have been done to analyze the antioxidant, antimicrobial, microbial DNA cleavage and enzyme inhibition activities of MPcs molecules conjugated with nanoparticles. In this essence, MPcs/ nanoparticle hybrids to attain high antimicrobial activity has become important in view of extensive consumption of man-made antibiotic medications following to subsequent drug resistance. In order to attain good results in all the above mentioned applications, attaining a good solubility in a wide range of organic solvents for phthalocyanines is a crucial stage. Limitations in high solubility arises due to the π stacking (clustering) between planar macrocycles. Therefore, unsubstituted phthalocyanines are insoluble or poorly soluble in organic solvents and water, prohibiting their application areas. Substitution at peripheral or axial sites of macrocycles increases the distance between their 18π-electron conjugated systems. Thus aggregation reduces and an increased solubility in various solvents is observed tending to improve their optical properties. Insertion of large side groups and longer alkyl chains helps enhancing the solubility and thus the optical properties of phthalocyanines. For gaining proper solubility and substantiality in MPcs, the terminal alkynyl group (C≡C) serves as an exemplary substituent and is known to provide excellent rigidity and significance in many optical related properties. In the span of this thesis work, 15 phthalocyanine compounds were prepared out of which four are asymmetrical, 5 symmetrical peripherally tetra-substituted and 6 are symmetrical peripherally octa-substituted metal phthalocyanines. These synthesized compounds were investigated for their potential use in photoconductive and biological applications. For this purpose, the phthalonitriles synthesized in this study for subsequent MPc substitution are; 4-(thiophen-3-ylethynyl) phthalonitrile (2), 4-[(4-pentylphenyl)ethynyl] phthalonitrile (3), of 4-{[4-(N,N-Dimethylamino)phenyl]ethynyl}phthalonitrile (5), Synthesis of 4,5-bis{[3,5 bis(trifluoromethyl)phenyl]ethynyl}phthalonitrile (6) and 4,5-bis((4-(dimethylamino)phenyl)ethynyl)phthalonitrile (7). For asymmetrical MPcs preparation, 4-(thiophen-3-ylethynyl) phthalonitrile (2) and 4-[(4-pentylphenyl)ethynyl] phthalonitrile (3) were reacted in statistical condensation fashion with 1,2-Dicyano-3,4,5,6-tetrafluorobenzene to attain A3B type push-pull type asymmetrical tetra-substituted Co and Zn MPcs. Latterly, symmetrical peripherally tetra-substituted MPcs (M= Co, Zn, Mn, Fe and Lu) were shaped from the prepared phthalonitrile derivative (5). Whereas, from the phthalonitriles (6) and (7) symmetrical peripherally octa-substituted phthalocyanines were gathered containing Co, Zn and Lu metal ions. To attain high purity of all the newly synthesized phthalonitrile derivatives and related phthalocyanines, they were subjected to thin layer, preparative and column chromatography. Furthermore, all of their structures were examined through distinct spectroscopic techniques such as FT-IR, NMR, MALDI-TOF and UV-vis spectroscopy. Electronic UV-vis spectra of the newly synthesized symmetrical phthalocyanines were reported in DMSO and THF solvent while for asymmetrical MPcs only THF was employed. Moreover, the effect of concentration and type of solvent (THF) on the spectral and aggregating properties of newly synthesized PcOFLu was investigated, as well. Photovoltaic cells consisting of ITO/PEDOT:PSS/Pc/Ag layers were designed from synthesized asymmetric phthalocyanines of phtahlonitrile (2) and (3) for photoconductive analysis are also a part of this thesis study. Phthalonitriles (5) and (7) and their respective Co and Zn MPcs were subjected to conjugation with gold nano particles (AuNPs) and assessed through the TEM analysis to elucidate the size and shape of these hybrid particles. All the synthesized MPc/AuNP hybrids, phthalonitrile (5) & (7) along with their related Co and Zn Pcs and AuNPs were analyzed for several biological studies including, anti-oxidant activity, biofilm inhibition, anti- microbial activity, microbial cell viability inhibition and DNA cleavage activity. All these studies concluded that using the MPc/AuNP hybrids for these biological applications gave better results for all the above mentioned biological applications rather than employing AuNPs alone.