Behavior of Binary Guests in a Porous Coordination Polymer

Controlling the condensed state of multiple guests in nanoporous media is critical to many applications, but an understanding of this phenomenon in pores smaller than a few nanometers is still unavailable. In this work, we investigate the aggregation state of binary guests, poly(ethylene glycol) (PEG), and long-chain normal alkanes, in subnanometer channels of a porous coordination polymer (PCP) by monitoring their thermal transition behaviors. PEG and alkanes are immiscible in the bulk and their melting transitions are not affected by each other. Meanwhile, in the PCP nanochannels, the transition temperature and the heat of the binary-guest system were significantly different from when PEG or an alkane was individually included. This suggests the formation of microscopically segregated domain structures of PEG and alkane in the host crystal. The transition behaviors gradually varied by changing the introduction ratio between PEG and alkane, and thus the aggregation states of the two guests were successfully controlled by the simple variation of relative amounts. This methodology offers a promising route to control spatial configurations of multiple guest molecules in nanoporous matrices for advanced applications.