LANGMUIR FILMS OF P-TERT-BUTYLCALIX[8]ARENE - CONFORMATIONS AT THE WATER-AIR INTERFACE AND COMPLEXATION OF FULLERENE C-60

Langmuir monolayers of p-tert-butylcalix[8]arene (CAL8) at the water-a ir interface were studied as a function of temperature (between 288 an d 308 K), of the spreading solvent (benzene, toluene, dichloromethane, chloroform, and carbon tetrachloride), and in a mixture with fulleren e C-60. Two different mixed systems were studied: (i) spreading isothe rms (surface pressure versus molecular area) after separated spreading of CAL8 and C-60 solutions (1/1 molar ratio) and (ii) spreading isoth erms of the C-60-CAL18 complex obtained from precipitation of freshly prepared and stabilized solutions of the two components in carbon tetr achloride. The results show that, at the water-air interface, CAL8 pos sesses a perpendicular ''pleated-loop'' conformation, regardless of th e spreading solvent. However, the limiting areas do depend on the natu re of the spreading solvent, indicating that the flexibility of the CA L8 backbone is significantly affected by the interactions with the spr eading solvent, in analogy with the ''memory effect'' with the retenti on of the host conformation, even after the removal of the guest, foun d for bulk solutions. The complexation of C60 by CAL8 does not modify the calixarene's conformation. Films obtained by spreading equimolar s olutions of CAL8 and C-60 on the water surface show the same II/A isot herms of the [C-60-CAL8] complex, suggesting the formation of stable C AL8/C-60 1/1 complexes at the air-water interface. Electronic spectra performed on Langmuir-Blodgett films and on collapsed material, both t ransferred on quartz plates, support the presence at the interface of the [C-60-CAL8] host-guest system, indicating that the water interface acts as a complexation promoter.