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Near-Infrared Organic Materials for Biological Applications
Published in Song Sun, Wei Tan, Su-Huai Wei, Emergent Micro- and Nanomaterials for Optical, Infrared, and Terahertz Applications, 2023
To date, various NIR fluorophores including some commercially available dyes such as ICG, IR-26, IR-783, IR-806, IR-1061, etc., have been successfully used for bioimaging, which may include precise organ/tissue imaging, tumor imaging, dynamic metabolism imaging, etc. For instance, Smith group synthesized a tetralactam macrocycle appended with six copies of a bone-targeting ligand [77]. By taking advantage of the host-guest self-assembly strategy, a linear fluorescent PEGylated squaraine dye could thread into two macrocycles and form a pseudorotaxane architecture. This pre-assembly strategy not only endowed the squaraine dye with better photostability, red-shifted absorbance and emission wavelength, targeting ability, but also provided targeting ability. Imaging results showed that there was no fluorescence attenuation at the bone sites after 24 hours in a living mouse, indicating the high targeting ability and chemical stability of this supramolecular NIR probe (Figure 14.11(a)). Tang and co-workers developed s series of semiconducting polymer nanoparticles (SPNs) that integrated planar π-conjugated groups and twisted units into one polymer system, thus achieved strong absorption coefficient and high aggregated-state fluorescence quantum yield [78]. Through this rational molecular design strategy, much brighter NIR-II (1300–1400 nm) emission was obtained for blood vessel imaging in vivo (Figure 14.11(b)). Another important issue in medicine is the imaging of tumor tissue, which demands fluorescent probes with the abilities to selectively label cancerous cells. A series of characteristic and abnormal metabolisms have been observed in tumor tissues, such as hypoxia, low pH, high energy-demand, high vasculature, over expression of biological receptors, and enhanced mitochondria activity, etc. [79]. Therefore, NIR fluorescent molecules that can specifically target or monitor these factors can be used for tumor delineation and imaging-guided surgery. Considering the better practical clinical applications, wash-free NIR fluorescence imaging is attracting more and more attention, because it can greatly simplify the preprocessing, shorten the detection time, as well as minimize the potential background interference. From this perspective, NIR fluorophores with AIE characters (AIEgens) should be promising candidates for this wash-free fluorescence imaging technology, because they are non-emissive in dilute solution, but emit intensely in the targeted and aggregated sites [80].
Multicolor upconversion luminescence of dye-coordinated Er3+ at the interface of Er2O3 and CaF2 nanoparticles
Published in Science and Technology of Advanced Materials, 2019
Ayumi Ishii, Yuya Adachi, Ayaka Hasegawa, Miyu Komaba, Shuhei Ogata, Miki Hasegawa
Here, the squaraine dye, 2,4-bis[8-hydroxyl-1,1,7,7-tetramethyl-julolidin-9-yl]squaraine (bjSQ), having a metal coordination site, was selected as a photosensitizer to enhance the upconversion emission of Er3+ (Figure 1(a)). Squaraine dyes, with their unique aromatic four-membered ring system derived from squaric acid, are a class of organic dyes that exhibit intense absorption (absorption coefficient: ɛ ≈ 3 × 105 cm−1M−1) and fluorescence bands (luminescence quantum yield: ϕ ≈ 0.65), typically in the red and near-IR regions [18]. Two core nanoparticles with different vibration modes (Er2O3 and CaF2) were selected to construct the interface of the dye-coordinated nanoparticles. In the oxide state, which is the most stable in Ln compounds, the surface conditions may strongly affect the relaxation pathways of Ln3+ since the vibration energy of the hydroxyl group (-OH) in adsorbed (or hydrated) H2O on the surface matches well with some transition energies of Ln3+. On the other hand, CaF2 nanoparticles as the core can suppress the vibration deactivation pathway in the upconversion process due to their low phonon energy, high refractive index, optical transparency, and high chemical and thermal stabilities [19–22].
Recent advances with optical upconverters made from all-organic and hybrid materials
Published in Science and Technology of Advanced Materials, 2019
Roland Hany, Marco Cremona, Karen Strassel
A photodetector with peak sensitivity at 980 nm and an internal photon-to-current conversion efficiency of close to 100% under reverse bias was demonstrated with a NIR-selective squaraine dye (SQ-880):PC61BM blend, where PC61BM denotes [6,6]-phenyl-C61-butyric acid methyl ester [25]. The photodetector was integrated in an upconverter by using a MoO3 hole transport layer to facilitate charge injection into the Alq3 emitter. The materials of this organic upconverter absorb very little in the visible. By using a semitransparent top electrode, visibly transparent devices could be fabricated with an average visible transmittance of 65% and a peak transmittance of 80% at 620 nm.
Dual colorimetric and fluorescent determination of iron (III) using a novel squaraine dye
Published in Instrumentation Science & Technology, 2018
Chen Zhang, Mengyuan Wang, Yuzhe Zhang, Zhongyu Li, Song Xu
Herein, a novel squaraine compound 6-carboxy-2-[[3-[(1,3-dihydro-3,3-dimethyl-1-ethyl-2H-indol-2-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-3,3-trimethyl-3H-indolium as an on–off fluorescent probe for detecting Fe3+ in CH3CH2OH/H2O (4:1, v/v) is reported. The squaraine dye is much highly selective and sensitive to Fe3+ ions and the corresponding signal is displayed by the change of fluorescence. The optical properties are studied by the fluorescence emission and absorption spectra. Squaraine dye dramatically displays ascendant sensitivity and reversibility for sensing Fe3+.