ISSN:
0947-6539
Keywords:
cryo-transmission electron microscopy
;
monolayers
;
oligothiophenes
;
polymorphism
;
scanning force microscopy
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The formation of Langmuir monolayers at the air-water interface has long been believed to be limited to amphiphilic molecules containing a hydrophobic chain and a hydrophilic headgroup. Here we report the formation of crystalline mono- and multilayer self-assemblies of oligothiophenes, a class of aromatic nonamphiphilic molecules, self-aggregated at the air-water interface. As model systems we have examined the deposition of quaterthiophene (S4), quin-quethiophene (S5), and sexithiophene (S6) from chloroform solutions on the water surface. The structures of the films were determined by surface pressure-area isotherms, by scanning force microscopy (SFM) after transfer of the films onto atomically smooth mica, by cryo-transmission electron microscopy (Cryo-TEM) on vitreous ice, and by grazing incidence synchrotron X-ray diffraction (GID) directly on the water surface. S4 forms two polymorphic crystalline multilayers. In polymorph α, of structure very similar to that of the three-dimensional solid, the molecules are aligned with their long molecular axis tilted by about 23° from the normal to the water surface. In polymorph β the long molecular axis is perpendicular to the water surface. S5 self-aggregates at the water surface to form mixtures of monolayers and bilayers of the β polymorph; S6 forms primarily crystalline monolayers of both α and β forms. The crystalline assemblies preserve their integrity during transfer from the water surface onto solid supports. The relevance of the present results for the understanding of the early stages of crystal nucleation is presented.
Additional Material:
13 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19970030615
