Hydrogen bonding boosted the persistent room temperature phosphorescence of pure organic compounds for multiple applications

Persistent room temperature phosphorescence (p-RTP) of pure organic compounds is drawing much attention due to its unique advantages and promising applications in anticounterfeiting, encryption, bioimaging, etc. Achieving efficient p-RTP, however, remains challenging. In this contribution, we designed and synthesized three benzoic acid-carbazole conjugates, 4-BACZ, 3-BACZ and 2-BACZ, with strong hydrogen bonding and a dimer structure in their crystals. Compared with their ester counterparts, whose highest RTP efficiency (Φ_p) is 2.6%, these acids exhibit significantly boosted Φ_p of 6.9%, 3.4% and 2.6% for 4-BACZ, 3-BACZ and 2-BACZ, respectively. Such enhancement should be ascribed to the effective and abundant hydrogen bonding in the crystals, which significantly depressed the vibrational dissipation. This effect is also confirmed by the theoretically calculated much lower reorganization energies. These crystals are also readily fabricated into biocompatible nanoparticles (NPs) with an inherited p-RTP characteristic. Such a p-RTP feature of the crystals and the NPs makes them highly promising for versatile applications. Herein, the application of these materials in anticounterfeiting and high resolution in vivo afterglow bioimaging is demonstrated.