One-pot catalyst-free synthesis of down- and upconversion fluorescent oligopyrazolines from diazoacetates and maleic anhydride

Abstract

Conventionally, each fluorophore is only illuminated with the wavelength of incident light shorter (downconversion) or longer (upconversion) than that of emitted light. However, the oligopyrazolines presented in this paper are the down-and upconversion fluorescent molecules with a maximum emission at 445 nm, which are facilely synthesized from diazoacetates and maleic anhydride (MA) without any catalyst by a newly developed one-pot process. The intermediates of oligopyrazolines are formed through 1,3dipolar cycloaddition and a cascade ring-opening insertion, which transform into oligomers in situ with molecular weight around 2 × 10 3 g mol −1 . The structures of the subunits and resulting oligopyrazolines are clarified clearly by MALDI-TOF-MS and the quantum yield with excitation at 350 nm is in the range of 12-19%. A cell experiment with HeLa cells demonstrates its promising potential for bioimaging applications. † Electronic supplementary information (ESI) available: The polymerization at different reaction times; 1 H NMR spectrum with the addition of deuteroxide; online FT-IR spectra, FT-IR spectra, MALDI-TOF-MS spectra, DSC curves, TG curves, XRD patterns, SEM images, UV-vis and fluorescent spectra of oligomers; the quantum yield of the obtained oligomers; down-and upconversion fluorescence at different excitation wavelengths and the whole excitation spectrum; cytotoxicity assay. See

Novel Synthesis of Down-/Up-Conversion Fluorescent Oligo(2-pyrazoline)s

“…Thus, in these oligomers the maximum excitation wavelengths excited by both down-conversion and up-conversion fluorescence are around the same region. To date, there have only been rare reports of organics with both down- and up-conversion fluorescence properties. ,− …”

“…This is the first example of fluorescent oligomer constructed by pyrazoline as the backbone. Recently, several researches proved that diazo-contained polymers may have unique optical properties, and they could emit both down-conversion fluorescence excited by visible light and the up-conversion fluorescence excited by near-infrared light, which is a potential field in optical materials. − …”

Copolymerization of alkyl diazoacetates with α,β-unsaturated aldehydes: synthesis and application

“…To date, there have only been rare reports of organic materials with both down-and upconversion fluorescence properties. [27][28][29][30][31] By density functional theory (DFT) calculations, it was ascertained that the fluorescence is mainly because of the electron radiation transition between intramolecular -NvNconjugations (see the ESI †).…”