The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials

This thesis entitled ‘The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials’ is divided in 6 Chapters. Chapter 1, squaramide based receptors as potential anion sensors, gives a brief introduction into the history of anion recognition and the significant role anions play in biology and in the environment. A range of relevant examples of anion receptors and sensors from the literature are also given. This Chapter concludes with the aims of the research conducted in Chapter 2. In Chapter 2, a set of novel squaramide based anion receptors are described. The synthesis of each receptor is discussed in addition to their photophysical and anion binding properties. Chapter 3, squaramide based low molecular weight gelators (LMWGs), gives a concise background into the field of gels, from their formation and classification to their characteristics. It also gives a brief introduction on the topic of supramolecular gels with some relevant examples from the literature. This Chapter concludes with the aims of the research conducted in Chapter 4. In Chapter 4, a series of novel squaramides potential low molecular weight oragano-gelators (LMWOGs) are described. The synthesis of each new compound is discussed, in addition to preliminary gelation tests. In Chapter 5, an overall conclusion of the entire preceding chapter is given. Finally, in Chapter 6, general experimental procedures are outlined and the synthesis and characterisation of each of the compounds is given. Subsequently, literature references are provided and are followed by the Appendix which provides spectroscopic, titration data and photographic images to support work described in the main text

The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials

This thesis entitled ‘The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials’ is divided in 6 Chapters. Chapter 1, squaramide based receptors as potential anion sensors, gives a brief introduction into the history of anion recognition and the significant role anions play in biology and in the environment. A range of relevant examples of anion receptors and sensors from the literature are also given. This Chapter concludes with the aims of the research conducted in Chapter 2. In Chapter 2, a set of novel squaramide based anion receptors are described. The synthesis of each receptor is discussed in addition to their photophysical and anion binding properties. Chapter 3, squaramide based low molecular weight gelators (LMWGs), gives a concise background into the field of gels, from their formation and classification to their characteristics. It also gives a brief introduction on the topic of supramolecular gels with some relevant examples from the literature. This Chapter concludes with the aims of the research conducted in Chapter 4. In Chapter 4, a series of novel squaramides potential low molecular weight oragano-gelators (LMWOGs) are described. The synthesis of each new compound is discussed, in addition to preliminary gelation tests. In Chapter 5, an overall conclusion of the entire preceding chapter is given. Finally, in Chapter 6, general experimental procedures are outlined and the synthesis and characterisation of each of the compounds is given. Subsequently, literature references are provided and are followed by the Appendix which provides spectroscopic, titration data and photographic images to support work described in the main text

Squaramide—Naphthalimide Conjugates as “Turn-On” Fluorescent Sensors for Bromide Through an Aggregation-Disaggregation Approach

The syntheses of two new squaramide-naphthalimide conjugates (SQ1 and SQ2) are reported where both compounds have been shown to act as selective fluorescence “turn on” probes for bromide in aqueous DMSO solution through a disaggregation induced response. SQ1 and SQ2 displayed a large degree of self-aggregation in aqueous solution that is disrupted at increased temperature as studied by 1H NMR and Scanning Electron Microscopy (SEM). Moreover, the fluorescence behavior of both receptors was shown to be highly dependent upon the aggregation state and increasing temperature gave rise to a significant increase in fluorescence intensity. Moreover, this disaggregation induced emission (DIE) response was exploited for the selective recognition of certain halides, where the receptors gave rise to distinct responses related to the interaction of the various halide anions with the receptors. Addition of F− rendered both compounds non-emissive; thought to be due to a deprotonation event while, surprisingly, Br− resulted in a dramatic 500–600% fluorescence enhancement thought to be due to a disruption of compound aggregation and allowing the monomeric receptors to dominate in solution. Furthermore, optical sensing parameters such as limits of detection and binding constant of probes were also measured toward the various halides (F−, Cl−, Br−, and I−) where both SQ1 and SQ2 were found to sense halides with adequate sensitivity to measure μM levels of halide contamination. Finally, initial studies in a human cell line were also conducted where it was observed that both compounds are capable of being taken up by HeLa cells, exhibiting intracellular fluorescence as measured by both confocal microscopy and flow cytometry. Finally, using flow cytometry we were also able to show that cells treated with NaBr exhibited a demonstrable spectroscopic response when treated with either SQ1 or SQ2

The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials

This thesis entitled ‘The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials’ is divided in 6 Chapters. Chapter 1, squaramide based receptors as potential anion sensors, gives a brief introduction into the history of anion recognition and the significant role anions play in biology and in the environment. A range of relevant examples of anion receptors and sensors from the literature are also given. This Chapter concludes with the aims of the research conducted in Chapter 2. In Chapter 2, a set of novel squaramide based anion receptors are described. The synthesis of each receptor is discussed in addition to their photophysical and anion binding properties. Chapter 3, squaramide based low molecular weight gelators (LMWGs), gives a concise background into the field of gels, from their formation and classification to their characteristics. It also gives a brief introduction on the topic of supramolecular gels with some relevant examples from the literature. This Chapter concludes with the aims of the research conducted in Chapter 4. In Chapter 4, a series of novel squaramides potential low molecular weight oragano-gelators (LMWOGs) are described. The synthesis of each new compound is discussed, in addition to preliminary gelation tests. In Chapter 5, an overall conclusion of the entire preceding chapter is given. Finally, in Chapter 6, general experimental procedures are outlined and the synthesis and characterisation of each of the compounds is given. Subsequently, literature references are provided and are followed by the Appendix which provides spectroscopic, titration data and photographic images to support work described in the main text

The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials

This thesis entitled ‘The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials’ is divided in 6 Chapters. Chapter 1, squaramide based receptors as potential anion sensors, gives a brief introduction into the history of anion recognition and the significant role anions play in biology and in the environment. A range of relevant examples of anion receptors and sensors from the literature are also given. This Chapter concludes with the aims of the research conducted in Chapter 2. In Chapter 2, a set of novel squaramide based anion receptors are described. The synthesis of each receptor is discussed in addition to their photophysical and anion binding properties. Chapter 3, squaramide based low molecular weight gelators (LMWGs), gives a concise background into the field of gels, from their formation and classification to their characteristics. It also gives a brief introduction on the topic of supramolecular gels with some relevant examples from the literature. This Chapter concludes with the aims of the research conducted in Chapter 4. In Chapter 4, a series of novel squaramides potential low molecular weight oragano-gelators (LMWOGs) are described. The synthesis of each new compound is discussed, in addition to preliminary gelation tests. In Chapter 5, an overall conclusion of the entire preceding chapter is given. Finally, in Chapter 6, general experimental procedures are outlined and the synthesis and characterisation of each of the compounds is given. Subsequently, literature references are provided and are followed by the Appendix which provides spectroscopic, titration data and photographic images to support work described in the main text

The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials

This thesis entitled ‘The Synthesis and Study of Novel Squaramide Scaffolds: From Sensors to Soft Materials’ is divided in 6 Chapters. Chapter 1, squaramide based receptors as potential anion sensors, gives a brief introduction into the history of anion recognition and the significant role anions play in biology and in the environment. A range of relevant examples of anion receptors and sensors from the literature are also given. This Chapter concludes with the aims of the research conducted in Chapter 2. In Chapter 2, a set of novel squaramide based anion receptors are described. The synthesis of each receptor is discussed in addition to their photophysical and anion binding properties. Chapter 3, squaramide based low molecular weight gelators (LMWGs), gives a concise background into the field of gels, from their formation and classification to their characteristics. It also gives a brief introduction on the topic of supramolecular gels with some relevant examples from the literature. This Chapter concludes with the aims of the research conducted in Chapter 4. In Chapter 4, a series of novel squaramides potential low molecular weight oragano-gelators (LMWOGs) are described. The synthesis of each new compound is discussed, in addition to preliminary gelation tests. In Chapter 5, an overall conclusion of the entire preceding chapter is given. Finally, in Chapter 6, general experimental procedures are outlined and the synthesis and characterisation of each of the compounds is given. Subsequently, literature references are provided and are followed by the Appendix which provides spectroscopic, titration data and photographic images to support work described in the main text

Head vs. Tail Squaramide–Naphthalimide Conjugates: Self-Assembly and Anion Binding Behaviour

The syntheses of two squaramide–naphthalimide conjugates (SN1 and SN2) are reported; the structures of SN1 and SN2 differ by the attachment of a squaramide—either at the ‘head’ or the ‘tail’ of the naphthalimide fluorophore. Both compounds displayed weak fluorescence due to the inclusion of a nitro-aromatic squaramide which efficiently quenches the emission of the naphthalimide. Both compounds were also shown to undergo self-aggregation as studied by 1H NMR and scanning electron microscopy (SEM). Furthermore, SN1 and SN2 gave rise to stark colourimetric changes in response to basic anions such as AcO−, SO42− HPO42−, and F−. The observed colour changes are thought to be due to deprotonation of a squaramide NH. The same basic anions also result in a further quenching of the naphthalimide emission. No colour change or emission modulations were observed in the presence of Cl−; however, 1H NMR studies suggest that moderate H-bonding occurs between this anion and both SN1 and SN2

Head vs. Tail Squaramide–Naphthalimide Conjugates: Self-Assembly and Anion Binding Behaviour

The syntheses of two squaramide–naphthalimide conjugates (SN1 and SN2) are reported; the structures of SN1 and SN2 differ by the attachment of a squaramide—either at the ‘head’ or the ‘tail’ of the naphthalimide fluorophore. Both compounds displayed weak fluorescence due to the inclusion of a nitro-aromatic squaramide which efficiently quenches the emission of the naphthalimide. Both compounds were also shown to undergo self-aggregation as studied by 1H NMR and scanning electron microscopy (SEM). Furthermore, SN1 and SN2 gave rise to stark colourimetric changes in response to basic anions such as AcO−, SO42− HPO42−, and F−. The observed colour changes are thought to be due to deprotonation of a squaramide NH. The same basic anions also result in a further quenching of the naphthalimide emission. No colour change or emission modulations were observed in the presence of Cl−; however, 1H NMR studies suggest that moderate H-bonding occurs between this anion and both SN1 and SN2

Head vs. Tail Squaramide–Naphthalimide Conjugates: Self-Assembly and Anion Binding Behaviour

The syntheses of two squaramide–naphthalimide conjugates (SN1 and SN2) are reported; the structures of SN1 and SN2 differ by the attachment of a squaramide—either at the ‘head’ or the ‘tail’ of the naphthalimide fluorophore. Both compounds displayed weak fluorescence due to the inclusion of a nitro-aromatic squaramide which efficiently quenches the emission of the naphthalimide. Both compounds were also shown to undergo self-aggregation as studied by 1H NMR and scanning electron microscopy (SEM). Furthermore, SN1 and SN2 gave rise to stark colourimetric changes in response to basic anions such as AcO−, SO4 2− HPO4 2−, and F−. The observed colour changes are thought to be due to deprotonation of a squaramide NH. The same basic anions also result in a further quenching of the naphthalimide emission. No colour change or emission modulations were observed in the presence of Cl−; however, 1H NMR studies suggest that moderate H-bonding occurs between this anion and both SN1 and SN2. </p

Squaramide—Naphthalimide Conjugates as “Turn-On” Fluorescent Sensors for Bromide Through an Aggregation-Disaggregation Approach

The syntheses of two new squaramide-naphthalimide conjugates (SQ1 and SQ2) are reported where both compounds have been shown to act as selective fluorescence “turn on” probes for bromide in aqueous DMSO solution through a disaggregation induced response. SQ1 and SQ2 displayed a large degree of self-aggregation in aqueous solution that is disrupted at increased temperature as studied by 1H NMR and Scanning Electron Microscopy (SEM). Moreover, the fluorescence behavior of both receptors was shown to be highly dependent upon the aggregation state and increasing temperature gave rise to a significant increase in fluorescence intensity. Moreover, this disaggregation induced emission (DIE) response was exploited for the selective recognition of certain halides, where the receptors gave rise to distinct responses related to the interaction of the various halide anions with the receptors. Addition of F− rendered both compounds non-emissive; thought to be due to a deprotonation event while, surprisingly, Br− resulted in a dramatic 500–600% fluorescence enhancement thought to be due to a disruption of compound aggregation and allowing the monomeric receptors to dominate in solution. Furthermore, optical sensing parameters such as limits of detection and binding constant of probes were also measured toward the various halides (F−, Cl−, Br−, and I−) where both SQ1 and SQ2 were found to sense halides with adequate sensitivity to measure μM levels of halide contamination. Finally, initial studies in a human cell line were also conducted where it was observed that both compounds are capable of being taken up by HeLa cells, exhibiting intracellular fluorescence as measured by both confocal microscopy and flow cytometry. Finally, using flow cytometry we were also able to show that cells treated with NaBr exhibited a demonstrable spectroscopic response when treated with either SQ1 or SQ2