Impact of Shape Persistence on the Porosity of Molecular Cages.
Porous materials provide a plethora of technologically important applications that encompass molecular separations, catalysis, and adsorption. The majority of research in this field involves network solids constructed from multitopic constituents that, when assembled either covalently or ionically, afford macromolecular arrangements with micro- or meso-porous apertures. Recently, porous solids fabricated from discrete organic cages have garnered much interest due to their ease of handling and solution processability. Although this class of materials is a promising alternative to network solids, fundamental studies are still required to elucidate critical structure-function relationships that govern microporosity. Here, we report a systematic investigation of the effects of building block shape-persistence on the porosity of molecular cages. Alkyne metathesis and edge-specific postsynthetic modifications afforded three organic cages with alkynyl, alkenyl, and alkyl edges, respectively. Nitrogen adsorption experiments conducted on rapidly crystallized and slowly crystallized solids illustrated a general trend in porosity: alkynyl > alkenyl > alkyl. To understand the molecular-scale origin of this trend, we investigated the short and long time scale molecular motions of the molecular cages using ab initio molecular dynamics (AIMD) and classical molecular dynamics (MD) simulations. Our combined experimental and computational results demonstrate that the microporosity of molecular cages directly correlates with shape persistence. These findings discern fundamental molecular requirements for rationally designing porous molecular solids.
Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Timothy P
0000-0001-8881-1518
TP
Moneypenny
Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Nathan P
NP
Walter
Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Zhikun
Z
Cai
Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Yu-Run
YR
Miao
School of Chemical Sciences, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Danielle L
0000-0003-0059-2096
DL
Gray
Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Jordan J
JJ
Hinman
Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Semin
0000-0003-0873-9507
S
Lee
Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.|Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Yang
Y
Zhang
Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.|Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Jeffrey S
0000-0001-5841-6269
JS
Moore