Luminescent Metal‐Organic Frameworks for Selectively Sensing Nitric Oxide in an Aqueous Solution and in Living Cells

Abstract

Cu 2+‐based metal‐organic framework (Cu−TCA) (H 3TCA = tricarboxytriphenyl amine) having triphenylamine emitters was assembled and structurally characterized. Cu−TCA features a three‐dimensional porous structure consolidated by the well‐established Cu 2(O 2 CR)4 paddlewheel units with volume of the cavities approximately 4000 nm 3. Having paramagnetic Cu 2+ ions to quench the luminescence of triphenylamine, Cu−TCA only exhibited very weak emission at 430 nm; upon the addition of NO up to 0.1 m M, the luminescence was recovered directly and provided about 700‐fold fluorescent enhancement. The luminescence detection exhibited high selectivity – other reactive species present in biological systems, including H 2 O 2, NO 3−, NO 2−, ONOO−, ClO− and 1 O 2, did not interfere with the NO detection. The brightness of the emission of Cu−TCA also led to its successful application in the biological imaging of NO in living cells. As a comparison, lanthanide metal‐organic framework Eu−TCA having triphenylamine emitters and characteristic europium emitters was also assembled. Eu−TCA exhibited ratiometric fluorescent responses towards NO with the europium luminescence maintained as the internal standard and the triphenylamine emission exhibited more than 1000‐fold enhancement.