Luminescent ruthenium(II) polypyridyl complexes and BODIPY-perylene charge-transfer compounds possess several remarkable properties that make them attractive for a range of applications including cellular imaging and phototherapy. These properties include large Stokes shifts, a crucial characteristic for enhancing the signal-to-noise ratio in fluorescence imaging. Moreover, their versatile synthetic chemistry allows for tailored designs for enhanced cellular imaging or for maximizing therapeutic efficacy. For example, the ability of these charge-transfer luminophores to generate cytotoxic reactive oxygen species upon photoexcitation makes them promising candidates for photodynamic therapy. Presented in this thesis, are experimental findings on the Luminescent ruthenium(II) polypyridyl complexes and BODIPY-perylene charge-transfer compounds possess several remarkable properties that make them attractive for a range of applications including cellular imaging and phototherapy. These properties include large Stokes shifts, a crucial characteristic for enhancing the signal-to-noise ratio in fluorescence imaging. Moreover, their versatile synthetic chemistry allows for tailored designs for enhanced cellular imaging or for maximising therapeutic efficacy. For example, the ability of these charge-transfer luminophores to generate cytotoxic reactive oxygen species upon photoexcitation makes them promising candidates for photodynamic therapy. Presented in this thesis, are experimental findings on the phototherapeutic potential of a Ru(II) parent complex Ru-bqp-ester and its peptide conjugates Ru-bqp-MPP and Ru-bqp-R8, which showed exceptional phototoxicity across a range of cancer and non-cancer cell lines. Conjugation to cell penetrating and signal peptides is a useful strategy for promoting cellular uptake and targeting specific organelles such as the mitochondria or the nucleus, however, guanine quadruplexes (G4s) are gaining increasing interest as therapeutic targets. Two G4 targeted Ru(II) complexes, Ru-TAP-PDC3 and Ru-RHAU, were investigated as probes for imaging and phototherapy. Ru-TAP-PDC3 is the first Ru(II) complex directed toward photodamage of G4s located in the mitochondrial genome and Ru-RHAU is the first reported dye capable of live cell imaging of stress granules (SGs), binding to G4s and inducing SGs in a time and concentration dependent manner. Additionally, a family of iodinated and non-iodinated BODIPY compounds were tested as Luminescent ruthenium(II) polypyridyl complexes and BODIPY-perylene charge-transfer compounds possess several remarkable properties that make them attractive for a range of applications including cellular imaging and phototherapy. These properties include large Stokes shifts, a crucial characteristic for enhancing the signal-to-noise ratio in fluorescence imaging. Moreover, their versatile synthetic chemistry allows for tailored designs for enhanced cellular imaging or for maximising therapeutic efficacy. For example, the ability of these charge-transfer luminophores to generate cytotoxic reactive oxygen species upon photoexcitation makes them promising candidates for photodynamic therapy. Presented in this thesis, are experimental findings on the phototherapeutic potential of a Ru(II) parent complex Ru-bqp-ester and its peptide conjugates Ru-bqp-MPP and Ru-bqp-R8, which showed exceptional phototoxicity across a range of cancer and non-cancer cell lines. Conjugation to cell penetrating and signal peptides is a useful strategy for promoting cellular uptake and targeting specific organelles such as the mitochondria or the nucleus, however, guanine quadruplexes (G4s) are gaining increasing interest as therapeutic targets. Two G4 targeted Ru(II) complexes, Ru-TAP-PDC3 and Ru-RHAU, were investigated as probes for imaging and phototherapy. Ru-TAP-PDC3 is the first Ru(II) complex directed toward photodamage of G4s located in the mitochondrial genome and Ru-RHAU is the first reported dye capable of live cell imaging of stress granules (SGs), binding to G4s and inducing SGs in a time and concentration dependent manner. Additionally, a family of iodinated and non-iodinated BODIPY compounds were tested as potential photosensitisers, confirming a significant increase in phototoxicity upon iodination. A key aim of this thesis was to investigate the phototherapeutic potential of novel Ru(II) or BODIPY-based photosensitisers in live cells and multicellular tumour spheroids, and extend the application of these compounds for cellular imaging and sensing using confocal microscopy. potential photosensitisers, confirming a significant increase in phototoxicity upon iodination. A key aim of this thesis was to investigate the phototherapeutic potentialof novel Ru(II) or BODIPY-based photosensitisers in live cells and multicellular tumour spheroids, and extend the application of these compounds for cellular imaging and sensing using confocal microscopy.phototherapeutic potential of a Ru(II) parent complex Ru-bqp-ester and its peptide conjugates Ru-bqp-MPP and Ru-bqp-R8, which showed exceptional phototoxicity across a range of cancer and non-cancer cell lines. Conjugation to cell penetrating and signal peptides is a useful strategy for promoting cellular uptake and targeting specific organelles such as the mitochondria or the nucleus, however, guanine quadruplexes (G4s) are gaining increasing interest as therapeutic targets. Two G4 targeted Ru(II) complexes, Ru-TAP-PDC3 and Ru-RHAU, were investigated as probes for imaging and phototherapy. Ru-TAP-PDC3 is the first Ru(II) complex directed toward photodamage of G4s located in the mitochondrial genome and Ru-RHAU is the first reported dye capable of live cell imaging of stress granules (SGs), binding to G4s and inducing SGs in a time and concentration dependent manner. Additionally, a family of iodinated and non-iodinated BODIPY compounds were tested as potential photosensitisers, confirming a significant increase in phototoxicity upon iodination. A key aim of this thesis was to investigate the phototherapeutic potential of novel Ru(II) or BODIPY-based photosensitisers in live cells and multicellular tumour spheroids, and extend the application of these compounds for cellular imaging and sensing using confocal microscopy.