title: Light-harvesting and ultrafast energy migration in porphyrin-based metal-organic frameworks.
abstract: Given that energy (exciton) migration in natural photosynthesis primarily occurs in highly ordered porphyrin-like pigments (chlorophylls), equally highly ordered porphyrin-based metal-organic frameworks (MOFs) might be expected to exhibit similar behavior, thereby facilitating antenna-like light-harvesting and positioning such materials for use in solar energy conversion schemes. Herein, we report the first example of directional, long-distance energy migration within a MOF. Two MOFs, namely F-MOF and DA-MOF that are composed of two Zn(II) porphyrin struts [5,15-dipyridyl-10,20-bis(pentafluorophenyl)porphinato]zinc(II) and [5,15-bis[4-(pyridyl)ethynyl]-10,20-diphenylporphinato]zinc(II), respectively, were investigated. From fluorescence quenching experiments and theoretical calculations, we find that the photogenerated exciton migrates over a net distance of up to ~45 porphyrin struts within its lifetime in DA-MOF (but only ~3 in F-MOF), with a high anisotropy along a specific direction. The remarkably efficient exciton migration in DA-MOF is attributed to enhanced π-conjugation through the addition of two acetylene moieties in the porphyrin molecule, which leads to greater Q-band absorption intensity and much faster exciton-hopping (energy transfer between adjacent porphyrin struts). The long distance and directional energy migration in DA-MOF suggests promising applications of this compound or related compounds in solar energy conversion schemes as an efficient light-harvesting and energy-transport component.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Ho-Jin
authors.initials: HJ
authors.lastname: Son
authors.forename: Shengye
authors.initials: S
authors.lastname: Jin
authors.forename: Sameer
authors.initials: S
authors.lastname: Patwardhan
authors.forename: Sander J
authors.initials: SJ
authors.lastname: Wezenberg
authors.forename: Nak Cheon
authors.initials: NC
authors.lastname: Jeong
authors.forename: Monica
authors.initials: M
authors.lastname: So
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Wilmer
authors.forename: Amy A
authors.initials: AA
authors.lastname: Sarjeant
authors.forename: George C
authors.initials: GC
authors.lastname: Schatz
authors.forename: Randall Q
authors.initials: RQ
authors.lastname: Snurr
authors.forename: Omar K
authors.initials: OK
authors.lastname: Farha
authors.forename: Gary P
authors.initials: GP
authors.lastname: Wiederrecht
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Hupp
mesh_terms: D005453:Fluorescence; D008027:Light; D008665:Metalloporphyrins / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D008665:Metalloporphyrins; D009942:Organometallic Compounds; D015032:Zinc