p-Cymene–Ru(ii)–organometallic conjugates based on ‘V-shaped’ 4-amino-1,8-naphthalimide Tröger's base scaffolds: synthesis, photophysics, bioimaging, and BSA/HSA binding studies

Abstract

Three new p-cymene–Ru(II) organometallic conjugates (TB-Ru-1, TB-Ru-2, and TB-Ru-3) have been synthesised in good yield via metal–ligand coordination chemistry using three different freshly prepared fluorescent 4-amino-1,8-naphthalimide Tröger's base (TBNap) scaffolds (TBNap-1, TBNap-2, and TBNap-3). Standard spectroscopic techniques characterised the newly designed conjugates, and their molecular structures were obtained through computational optimisations. The photophysical studies of conjugates showed characteristic UV-visible absorption and fluorescence emission peaks. Moreover, the binding ability of conjugates towards Bovine Serum Albumin (BSA) and Human Serum Albumin (HSA) was probed by UV-visible absorption and fluorescence titration studies, which demonstrated substantial binding properties of the conjugates with BSA and HSA, resulting in a significant increase in absorption intensity and fluorescence quenching. The association constant (K_a) and fluorescence quenching constants (K_SV) were determined to be 10⁴ to 10⁵ M⁻¹. Additionally, cellular uptake studies using the 3T3 (embryonic mouse fibroblast) cell line demonstrated rapid internalisation with minimal cytotoxicity, suggesting the potential of these conjugates as bioimaging probes. These results underscore the possible applications of newly designed TBNap-based Ru(II) organometallic conjugates in biomedical fields.