Regioselective Synthesis of Emission Color‐Tunable Pyrazolo[1,5‐a]pyrimidines with β,β‐Difluoro Peroxides as 1,3‐Bis‐Electrophiles

The synthesis and photophysical properties of fluorescent pyrazolo[1,5‐a]pyrimidines (PPs) are explored. An array of 5,7‐disubstituted fluorescent PPs are prepared selectively by using β,β‐difluoro peroxides as the 1,3‐bis‐electrophiles. The synthesized PPs display a fairly significant stokes shift (up to 211 nm) and a large window of tunable emission wavelength that covers most of the visible spectrum (400 nm to 800 nm). Theoretical calculation indicates that the distinguished variation of intramolecular charge transfer (ICT) ability upon the varied substituents is responsible for the color‐tunable fluorescence emission. magnified image