squaric acid is also known as 3,4-dihydroxy-3-cyclobutene-1,2-dione. Melting point > 300 ℃ (decomposition at 293 ℃), white to beige crystalline powder. It is used as an intermediate in synthesizing organic photoconductor, liquid crystal display material, laser writing and recording material and electrostatic photography light receptor material. If used and stored according to regulations, it will not decompose and be sealed in a cool and dry environment.
It dyes are a kind of critical functional dyes. They have potential applications in solar cells, organic photoconductors, optical recording media, gas sensors and fluorescent biometrics. They are considered four vital useful dyes with phthalocyanine, anthocyanine, and azo dyes. It is reported that the research on squaric acid dyes mainly focuses on p-Diphenylamine squaric acid dyes, and the analysis of squaric acid cyanine dyes is not deep and systematic. Because the structure of squaric acid cyanine dyes is entirely different from p-Diphenylamine squaric acid dyes, it is essential to systematically study the structure, properties and functional application of squaric acid cyanine dyes in theory and practical application.
It does also have many advantages as a photosensitizer. For example, first, squaric acid can increase the absorption properties of photosensitizers; The second point is to improve the quantum yield of the triplet excited state of the sensitizer and the production of singlet oxygen; The third point is that square cyanine dyes can exhibit two-photon absorption; The fourth point is that square cyanine improves cell pharmacokinetics. The photodynamic window (600-850 nm) of natural cyanine dyes has strong absorption, which makes these dyes very suitable for sensitizers.
The main limitation of applying Squaric acid in biology is that the photophysical properties of squaric acid will be lost when nucleophiles attack the four rings. The polymerization of Chinese acid dyes in an aqueous environment is also a severe problem. These problems can be solved by using a suitable carrier-based drug delivery system, which improves the bioavailability of sensitizers and provides the necessary protection.