BASHY dyes as modular chromophores for multifaceted biorelevant applications: from imaging to photodynamic therapy

The multifactorial nature of biological systems and the ongoing effort to elucidate their underlying mechanisms have driven the demand for advanced fluorescent probes with high sensitivity and functional adaptability. To meet these challenges, multicomponent reactions (MCRs) offer a powerful synthetic strategy for the straightforward design of structurally diverse fluorophores with tunable chemical and photophysical properties. In this context, the boronic-acid derived salicylidenehydrazone (BASHY) platform has emerged as a versatile class of dyes featuring π-conjugated ligands coordinated to an sp³-hybridized boron centre. This molecular design yields fluorophores with polarity-sensitive emission and significant photostability. The modular scaffold allows the systematic tuning of photophysical properties, while preserving fluorescence efficiency upon derivatization. BASHY dyes display exceptional performance in bioimaging, enabling the labeling of lipid droplets (LDs), astrocytes, apoptotic cells, and myelin debris in in vivo demyelination models. The BASHY framework also supports energy-transfer cassettes (ETCs) with nearly quantitative energy transfer efficiencies and offers compatibility with fluorescence lifetime imaging microscopy (FLIM). Beyond imaging, BASHY dyes act as highly efficient singlet-oxygen photosensitizers (PSs) with potential applications in photodynamic therapy (PDT). Furthermore, specifically designed conjugates integrate both imaging and therapeutic functions, displaying potent cytotoxicity. In this review, we discuss the evolution of the BASHY platform and its applications that position these dyes as promising candidates for next-generation imaging and theranostic agents.