Examination of photoinduced radicals in two crystal forms of triphenylamine bis-urea macrocycles

Abstract

This study probes two solvates of triphenylamine (TPA) bis-urea macrocycle 1 and their activated structures to evaluate their maximum photoinduced radicals (PIRs), the subsequent decay of the radicals, and their regeneration. The hierarchical assembly of TPAs shows promise in stabilizing less substituted derivatives, potentially expanding the utility of TPAs that lack stabilizing para-substituents. Single crystal structure analysis reveals that host 1 adopts a planar conformation with the two ureas pointing in opposite directions when dimethoxyethane (DME) is encapsulated within the channel. Whereas previously, 1 adopted a bowl-shaped conformation with the two ureas pointing in the same direction (syn) with dimethylsulfoxide (DMSO) bound within the channels. Removal of the guests gives identical activated structures. The bulk materials of 1 are characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Finally, the process of radical generation under UV-irradiation, decay, and regeneration of radicals was monitored by electron paramagnetic resonance (EPR) spectroscopy. While macrocycle conformation and extended structure are important, the presence of guests was most significant for PIR percentages.