Photo-induced organic radical species in naphthalenediimide-based metal-organic framework for reversible photochromism and near-infrared photothermal conversion

Abstract

Multifunctionality and adjustability of the stimulating responsive materials are the main reasons that make them so useful for practical application. In this paper, an inimitable crystalline metal-organic framework with both reversible photochromism and near-infrared photothermal conversion was successfully obtained by one-pot synthesis. Single-crystal structural analysis indicates that the naphthalenediimide(NDI)-based metal-organic framework is of significant lone pair-π interactions leading to the occurrence of effective electron delocalization in the photo-generation of charge-separation state for this crystalline material; simultaneously, the framework possesses hydrophobic cavities among the periodical NDI arrangements giving rise to effective structural separation. Consequently, the photo-generated colored radical anions can be recovered to corresponding light-colored neutral molecules in the existence of ozone or dark treatment, giving rise to reversible photochromic behavior for the crystalline framework. On the other hand, the unpaired electron can be delocalized across the π-system due to the existence of significant lone pair-π interactions in framework, in consequence of which irradiated sample undergoes a relatively small loss of organic radical anions after keeping in open air for at least 20 days. Atmospheric-stable organic radical anions with near-infrared absorption can be further used for photothermal conversion. This work provides in-depth insight into the correlation of charge-separation and the whole performance of materials and also extends the near-infrared photothermal conversion application of radical-doped crystalline materials.