Surface pressure and surface potential isotherms of ytterbium bisphthalocyanine Langmuir monolayers

A systematic study is reported on the monolayer characteristics of ytterbium bisphthalocyanine (YbPc2) at the air-water interface, using surface pressure and surface potential isotherms. The influence of various experimental parameters was analyzed, including compression speed, spreading volume, position of the pressure sensor, and subphase temperature. The area per molecule decreased with increasing spreading volumes. Interestingly, the position of the Wilhelmy plate affected the pressure-area isotherms, which does not occur for traditional aliphatic compounds. No significant influence from the subphase temperature was detected. Upon varying the compression speed, the surface potential curve and the collapse pressure were affected, even though the area per molecule remained practically the same. When these monolayers with distinct dipole moments were transferred onto a gold-coated glass substrate, the resulting multilayer LB films exhibited the same surface potential, probably:due to molecular rearrangement upon transfer.