Riassunto analitico
Object of the present research is the study of some indole-based
photorefractive (PR) materials. Novel indole-based NLO chromophores have
been synthesized and their photoconductive (PC) and PR behaviour have been
investigated when employed both alone (as low molecular weight glass
forming multifunctional PR moieties) as well as in blends with a PC
indolyl polymer, namely poly-(N-vinyl-2,3-dimethylindole). The aim was to
get more insight in the onset of PR effect and to evaluate various
contributions to it related to intermolecular interactions occurring among
the components of a PR material. The introduction of increasing contents
of polymer counterpart in PR blends containing the novel NLO chromophores
permitted to follow these interactions in their onset and the
establishment of new supramolecular arrangements, expected to be
responsible for dramatic changes of electrooptic properties. In this way,
it has been also possible to look for the proper formulation in order to
take advantage of such interactions for the achievement of the best PC and
PR performances. The joint analysis of the results of PC, PR and thermal
(DSC) behaviour of the investigated materials revealed itself as
particularly useful, due to the complexity of the many processes occurring
simultaneously in organic PR materials. A careful comparison with numerous
theoretical treatments permitted to rationalize the obtained results and
to put in evidence the prominent role played by intermolecular
interactions. On the other hand, the obtaining of long-term phase
stability of amorphous PR materials, desirable for their practical use in
a number of applications, was also a challenge. Many PR materials
described in the past, indeed, although having good photorefractive
properties, showed the undesirable drawback of fast recrystallization of
one or more of their molecular components, leading to opacization of films
and to the rapid loss of PR properties. Such aspect has been faced during
this research obtaining indefinitely stable materials. As concerns PR,
very large values of the photorefractive optical gain Γ (a main PR
figure of merit) have been achieved in many cases, classifying the
materials object of this research among the most efficient PR materials.
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