Boron neutron capture therapy (BNCT) is a promising binary approach to cancer treatment that exploits the ability of the non-radioactive ¹⁰B isotope to capture thermal neutrons. The resulting nuclear reaction releases high-energy particles over a very short range, enabling localized damage to cells containing ¹⁰B while potentially minimizing the exposure of surrounding healthy tissue [1].

The limited success of early clinical BNCT trials has been attributed, among other factors, to the lack of boron delivery agents with favorable pharmacokinetic properties and sufficient tumor selectivity, as well as to limitations in monitoring and visualizing boron accumulation in biological systems. An effective BNCT agent should selectively accumulate in tumor cells and deliver a sufficient amount of boron to the target tissue. Therefore, the ability to monitor the biodistribution and cellular localization of boron-containing compounds remains an important challenge [1]. One strategy to address this issue is the development of multifunctional molecular systems combining boron-rich clusters with intrinsically fluorescent chromophores, thereby integrating boron delivery and optical detection within a single molecular platform.

Among the wide variety of fluorescent organic chromophores, boron-dipyrromethene (BODIPY) dyes are particularly attractive due to their high fluorescence efficiency, photochemical stability, and readily tunable optical and structural properties [2]. Their molecular framework can be modified by introducing electron-donating and electron-withdrawing substituents at different positions, enabling modulation of the absorption and emission properties and providing functional sites for further conjugation [3]. These characteristics make BODIPY derivatives promising building blocks for the construction of fluorescent boron-cluster conjugates intended for BNCT-related applications.

Herein, we report the synthesis of a new BODIPY-based near-infrared (NIR) dye, BODIPY-Ph, exhibiting an absorption maximum at λ_abs = 669 nm. The target compound was successfully synthesized in 45% yield. BODIPY-Ph was specifically designed to serve as an NIR-active molecular scaffold for subsequent functionalization with boron-rich clusters. The resulting conjugates are expected to combine the high boron content required for neutron capture with the advantageous optical properties of the BODIPY chromophore, thus enabling optical detection and monitoring alongside their potential application in BNCT.