V. Dacosta et al., THIN-FILM ORIENTATION BY EPITAXY OF CARBAZOLYL POLYDIACETYLENES - GUEST-HOST INTERACTION ON A CRYSTAL-SURFACE, Macromolecules, 31(5), 1998, pp. 1635-1643
We investigated the oriented overgrowth of a series of diacetylene mol
ecules by epitaxy on a single crystal of potassium acid phthalate (KAP
). By changing the chemical architecture of the deposited molecule, we
were able to modify the molecular interactions between the deposited
molecule and the crystal surface. Thus we synthesized four new asymmet
rical diacetylenes (DA) bearing a carbazolyl group on one side of the
diacetylene core and a urethane at the end of a flexible spacer on the
other side Of the DA moiety. The different conditions of the film gro
wth under high vacuum were implemented by a systematic investigation o
f the different kinetic parameters acting on the molecule arrangement
at the crystal surface, such as the monomer evaporation rate or the su
bstrate temperature. The morphology and the structure of the films wer
e studied by atomic force microscopy (AFM) imaging and transmission el
ectron microscopy (TEM) and compared to the morphologies of the bis(ca
rbazolyl) derivative {poly[1,6-bis(9-carbazolyl)-2,4-hexadiyne], abbre
viated pDCH}. We found, for the monosubstituted carbazolyl derivative
{poly[9-(9-carbazolyl)-5,7-nonadiyn-1-ol ethylurethane], abbreviated (
pCNEU)}, that the molecular interactions leading to epitaxy were of se
veral types on the (010) plane of KAP. First, a pi-pi type interaction
induced one prevailing position of the DA molecules (the aromatic sid
es of the carbazolyl substituent were inserted between phenyl rows of
KAP stacked along c). Second, another geometrical interaction induced
two secondary positions of the DA molecules (the flexible moiety lying
in shallow ditches lined along the (101) directions of KAP). Related
to the thin film morphologies, the static optical spectroscopies were
also investigated and discussed. Improvements in orientational order w
ere observed on pCNEU as on pDCH at slow evaporation rates and on heat
ing the crystal substrate in the temperature range 50-100 degrees C.