Engineering the BASHY Dye Platform toward Architectures with Responsive Fluorescence

Abstract

A set of nine boronic‐acid‐derived salicylidenehydrazone (BASHY) complexes has been synthesized in good to very good chemical yields in a versatile three‐component reaction. In an extension to previous reports on this dye platform, the focus was put on the electronic modification of the “vertical” positions of the salicylidenehydrazone backbone. This enabled the observation of fluorescence quenching by photoinduced electron transfer (PeT), which can be reverted by the addition of acid in organic solvent (OFF‐ON fluorescence switching). The resulting emission is observed in the green‐to‐orange spectral region (maxima at 520–590 nm). In contrast, under physiological pH conditions in water, the PeT process is inherently decativated, thereby enabling the observation of fluorescence in the red‐to‐NIR region (maxima at 650–680 nm) with appreciable quantum yields and lifetimes. The latter characteristic supported the application of the dyes in fluorescence lifetime imaging (FLIM) of live A549 cells.

BASHY Dyes Are Highly Efficient Lipid Droplet-Targeting Photosensitizers that Induce Ferroptosis through Lipid Peroxidation

“…Noteworthily, the integration of the cholesterol moiety in 4 does not alter the photophysical properties as compared to dye 3 . This is in accordance with our previous finding that the photophysics of BASHY dyes is principally governed by the electronic properties of the salicylidenehydrazone backbone. , …”

“…This is in accordance with our previous finding that the photophysics of BASHY dyes is principally governed by the electronic properties of the salicylidenehydrazone backbone. 14,16 The dyes absorb with maxima at about 470 to 520 nm and, thus, can be conveniently excited in the visible spectral range by blue or green light. The absorption maximum is red-shifted with increasing degree of π-conjugation, according to the expectations of the cyanine-like character.…”

“…Recently, we developed a modular fluorescent platform based on boronic acid-derived salicylidenehydrazone complexes (BASHY) that absorb at wavelengths >450 nm, display high molar absorption coefficients (up to 70,000 M –1 cm –1 ), and show polarity-dependent emission in the green-to-red spectral range. , − More importantly, the hydrophobic BASHY dyes were shown to effectively accumulate in LDs . These structures are spherical cytoplasmic organelles composed of a neutral lipid core, which play a key role in tumor metabolism and act, among other functions, as lipid reserves to sustain the fast proliferation of cancer cells .…”