Silicon-substituted xanthene dyes and their applications in bioimaging

Abstract

Fluorescence imaging is one of the most powerful techniques for visualizing temporal and spatial changes of biological phenomena in living cells, and many fluorescent probes have been developed. In particular, xanthene dyes such as fluorescein and rhodamines have favorable characteristics, such as high water solubility, high fluorescence quantum yield and high molar extinction coefficient, and they have been utilized as fluorescent cores for fluorescent probes working in the green to red wavelength region. Recently, silicon-substituted xanthene dyes such as 2,7-N,N,N',N'-tetramethyl-9-dimethyl-10-hydro-9-silaanthracene (TMDHS), Si-rhodamines and TokyoMagentas, in which the O atom at the 10-position of xanthene is replaced with a Si atom, have been developed as novel far-red to near-infrared fluorescent cores that retain the key advantages of the parent structures. Fluorescent probes based on them have opened up new possibilities for imaging biological processes in living cells. This minireview covers recent progress in silicon-substituted xanthene dyes, including representative applications for in vivo tumor imaging, triple-color imaging of neuronal activity, and super-resolution microscopy.

Near‐Infrared Phosphorus‐Substituted Rhodamine with Emission Wavelength above 700 nm for Bioimaging

“…In the 1 H NMR spectra, hydrogen atoms from the methyl group bonded to the phosphorus atom (P‐Me) split into a doublet resonating at approximately δ =2 ppm with J H−P ≈13 Hz 17. 18 With NEt 2 ‐MDPP and PX in hand, we designed and synthesized Me‐PR by inserting 2‐methyl phenyl at the 9‐position of the xanthene core through a condensation process with NEt 2 ‐MDPP19 or a typical organometallic addition to PX 5b. Both approaches lead to the desired product; the former through a simpler procedure and the later with higher yields.…”

Selective Conversion of P=O‐Bridged Rhodamines into P=O‐Rhodols: Solvatochromic Near‐Infrared Fluorophores

“…The photobleaching resistance of 2 b – 2 e was assessed by monitoring the absorbance change upon irradiation with a Xe lamp (350 mW cm −2 ) in PBS buffer (pH 7.4; initial absorbance at the maxima: ≈0.2) and compared to those of cyanine 5.5 and o ‐tolyl‐substituted Si‐rhodamine (SiR) (Figure S17 and S18 in the Supporting Information). Among the PORL derivatives, 2 d with a carboxy group, which should exist in an anionic form under the experimental conditions, proved to be the most stable, that is, degradation was not observed even after continuous irradiation for 2 h. The other PORL derivatives also exhibited very high photostability, similar to or slightly better than that of SiR (≈5 % decomposition after 2 h), which is a representative far‐red‐emissive fluorophore with high photobleaching resistance that is widely used in modern fluorescence imaging . On the other hand, POF derivatives 3 b and 3 c showed slightly lower photobleaching resistance; that is, after irradiation for 2 h, photodegradation of 23 and 37 % was observed for 3 b and 3 c , respectively.…”

A Three‐Component Assembly Promoted by Boronic Acids Delivers a Modular Fluorophore Platform (BASHY Dyes)

“…Highly fluorescent dyes based, for example, on rhodamine,6, 7 fluorescein,3, 8 oxazine,3 coumarin,3 cyanine9, 10 or boron dipyrromethene (BODIPY)11, 12, 13, 14, 15 chromophores, have been extensively explored along these lines. In particular, BODIPY derivatives (Scheme 1 A) became the focus of different fields due to a combination of remarkable photophysical properties, which included very high quantum yields, narrow absorption and emission bands, and high molar absorption coefficients.…”