QCM analyses on adsorption of gaseous guests to cast films of porphyrin-resorcinol derivatives

Bindings of fourteen kinds of gaseous guests to cast films of Zn-porphyrin-bis (resorcinol) have been investigated by gravimetric analysis using a quartz crystal microbalance (QCM). The Zn-porphyxin-bis (resorcinol) is known to form a hydrogen bonded inclusion complex with appropriate guests. When a QCM with the cast film of the Zn-poxphyrin-bis (resorcinol) was exposed to flow of guest gas, the QCM showed frequency decreases proportional to the mass increase upon the guest binding. The cast film showed clear binding selectivity, which depends on whether the guest can form hydrogen bond with resorcinol OH and coordination to Zn. Ketones, esters, cyclic ethers, and pyridine efficiently bound to the cast film, while bindings of hydrocarbons, chloroform, and linear ether were hardly detected. Size-dependence in guest selectivity implies that cavity size is crucial factor on guest binding. Binding of large guests requires construction of extended host cavity, resulting in a large cooperativity. Binding to the other host, anthracene-bis (resorcinol) and Zn-porphyrintetrakis (resorcinol), was similar to that of the Zn-porphyrin-bis (resorcinol), but binding, stoichiometry showed dependence on size of host cavity. (C) 2000 Elsevier Science B.V. All rights reserved.