PHOTODIODES CONSTRUCTED BY LB FILMS OF POLYIMIDES POSSESSING TRIPHENYLAMINE UNITS

Diaminotriphenylamines 4 possessing four different substituents were n ewly synthesized, and introduced to polyamic acids 6 by the reaction w ith aliphatic tetracarboxylic dianhydride 5. The LB films of polyimide s 8 having triphenylamine units were fabricated on a glassy carbon ele ctrode via the LB films of long chain alkylamine salts of 6 to measure cyclic voltammograms. The methoxy substituted triphenylamine afforded the lowest redox potential, that suggested the highest electron densi ty on the nitrogen atom of the triphenylamine. The photoconductive dev ices (photodiodes) were constructed by the deposition of polyimides wh ich possessed different chemical structure, i.e., triphenylamines as a n electron donor (D), tetraphenylporphyrin as a sensitizer (S), and ar omatic polyimide as an electron acceptor (A), giving polyimide LB mult ilayer films. Two types of photodiodes having E/D/S/A and E/A/S/D were prepared on the semitransparent gold electrodes (E). When the methoxy substituted triphenylamine was used as D layer, the highest photocurr ent of 3 muA/cm2 was obtained. The order of magnitude of photocurrent was in good agreement with the results of cyclic voltammometry. The de pendence of numbers of D, S, and A layers on the photocurrent was exam ined by changing the number of each layer. It was found that the triph enylamine units had excellent electron donating ability and hole mobil ity, whereas the S and A layers did not transfer electron effectively.