Cyanine‐Like Boronic Acid‐Derived Salicylidenehydrazone Complexes (Cy‐BASHY) for Bioimaging Applications

Abstract

Boronic acid‐derived salicylidenehydrazone complex (BASHY) dyes with a polymethine backbone were designed to yield efficient red‐emitting and two‐photon absorbing fluorophores that can be used as markers for astrocytes. The dyes are chemically stable in aqueous solution and do not undergo photodecomposition. Their photophysical properties can be electronically fine‐tuned and thereby adapted to potentially different imaging situations and requirements.

Discovery of a size-record breaking green-emissive fluorophore: small, smaller, HINA

“…7-azaindole (7AI, 15 atoms) and SA (15 atoms) are to the best of our knowledge the smallest green-emitting fluorophores that have been reported so far, but they require the use of an unphysiological basic pH of >13.5 and >8.4, respectively. [40][41][42] SA is structurally closely related to HINA (14 atoms) but shows despite its more electron-rich phenyl ring somewhat counterintuitively a hypochromic shifted absorbance and emission spectra (Figure 1e-f). Compared to HINA, SA is an inferior fluorophore because its neutral form is not fluorescent and its anionic form is seven times weaker emissive (QY = 2% at pH 10.0).…”

Bis-borylated arylisoquinoline-derived dyes with a central aromatic core: towards efficient fluorescent singlet-oxygen photosensitizers

“…50-100 GM) [53][54][55] or the BASHY dye family (ca. 150-200 GM), 56,57 although more efficient 2PA-active boroncontaining chromophores are known. 58,59 The 2PA spectra (dividing the wavelengths by 2) do not compare with the longwavelength band of the one-photon absorption spectra.…”

BASHY Dye Platform Enables the Fluorescence Bioimaging of Myelin Debris Phagocytosis by Microglia during Demyelination

“…BASHY dyes (see structures of the herein employed compounds in Figure 1A) constitute an innovative and versatile platform of fluorophores that can be tailored for the specific needs of bioimaging applications [19,29,30]. These dyes consist of a salicylidenehydrazone ligand that is conformationally locked by reaction with a boronic acid component leading to a rigid non-planar structure.…”

“…Remarkably, the dyes show a pronounced light-up effect when transferred from a polar to an apolar environment [19]. This functionally very attractive aspect is ascribed to the push-pull character of BASHY, which is paired with cyanine-like behavior [30]. The relatively low stability of td1 against hydrolysis (half-life less than 10 min) can be alleviated by proper substitution at the electrophilic imine carbon, as shown for the dye td2 (half-life of ca.…”

“…3.5 h). On extension of the π-conjugation of td2, leading to the cyanine-like chromophores td3 and td4, the hydrolytic stability can be further improved for second-generation BASHY dyes (only 5% hydrolysis after 3 h in 10 mM phosphate-buffered saline at pH 7.4 as reaction medium) [30]. The stability data are summarized in Supplementary Table S1.…”