Given that energy migration in natural photosynthesis is generated by highly-ordered porphyrin pigments (chlorophylls), equally highly ordered porphyrin-based metal�organic frameworks (MOFs) might exhibit similar behavior. Ideally a MOF-based strategy could facilitate antenna-like light-harvesting and position such materials for solar energy conversion. Previously, we reported that in a metalloporphyrin-based, pillared-paddlewheel type MOF, DA-MOF , a photo-generated exciton can migrate up to 45 porphyrin struts within its lifetime and with a high anisotropy along a preferred direction. However, incorporating single crystals of DA-MOF  into films, a structure relevant to solar energy conversion devices, is a significant challenge. Herein, we report the first synthesis of an oriented thin film of DA-MOF  on a functionalized substrate using a solution-based layer-by-layer (LbL) approach. Profilometry measurements confirm that the film thickness increases linearly as a function of growth cycle. Further, polarized fluorescence measurements indicate that the overall transition dipole moments along the porphyrin are aligned in the DA-MOF film. Given that there are currently few methods capable of synthesizing a microporous MOF containing a coordination-site-accessible, free-base porphyrin, it is noteworthy that the LbL growth opens another pathway to synthesizing MOFs containing unmetalated porphyrins; this is indicated by the retention of four distinct Q bands in UV-vis absorption measurements. The results presented here promise useful insights for fabrication of MOF-based energy conversion devices in the future.

Layer-by-layer fabrication of an oriented thin film based on a porphyrin-containing metal organic framework

246th National Meeting (2013)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.