A Spiro‐Containing 7‐Hydroxy‐Carbocoumarin: Facile Two‐Step Synthesis and Enhanced Long‐Wavelength Fluorescence Properties

Abstract In contrast to the behavior of oxycoumarins, carbocoumarins can exhibit a maximum absorption wavelength which is more red‐shifted into the visible region. However, the fluorescence quantum yield decreases at the same time, restricting their further applications as long‐wavelength fluorophores. Herein, we developed a facile two‐step approach containing [4+1] spiroannulation and deprotection to simply and efficiently synthesize a novel spiro‐containing 7‐hydroxy‐carbocoumarin. Remarkably, with the aid of the rigid spiro structure, the spectral properties of our compound are comprehensively improved compared with previously reported carbocoumarins. The absorption and emission wavelengths show a further red‐shift, and the fluorescence quantum yield also increases significantly by 43 %. Our research not only enriches the database of carbocoumarins with a rapid and convenient synthetic strategy, but also sheds light on the rational design of carbocoumarins with superior spectral properties.