Shape-Persistent Phenylene-Ethynylene Macrocycles Spectroscopy and Dynamics: From Molecules to the Hydrogen-Bonded Organic Framework Material

Shape-persistent phenylene-ethynylene macrocycles are being intensively studied since they are being used for making hydrogen-bonded organic frameworks (HOFs). Here, we report on studies of two expanded macrocycles, Ex-COOH and Ex-COOMe (its methyl ester), in solutions and in the solid state (HOF Ex-apo and Ex-ester, respectively). For Ex-COOH, the theoretical results suggest the occurrence of an excited-state intramolecular charge-transfer in agreement with the experimental observation. While this event occurs in <200 fs in Ex-COOH in DMF solution, it becomes longer (similar to 2.5 ps) in Ex-COOMe. The formed species in the latter case shows a fluorescence lifetime of 2.02 ns, however for Ex-COOH, we found lifetimes of 0.4, 2.2, and 5.95 ns. Nanosecond-flash photolysis studies of Ex-COOH reveal two triplets having lifetimes of 0.45 and 2 mu s. The ensemble solid studies indicate that their photobehaviors are affected by the presence of different fluorescent emitters. Moreover, at the single crystal level, the emission spectra and decays of washed HOF Ex-apo crystals do not depend on the interrogated site. These results provide new insights into the photobehavior of both macrocyclic units of HOF Ex-apo. The findings will help for future researches and development of smart devices based on this kind of materials.