21 January 2000 Ž . Chemical Physics Letters 316 2000 343–348 www.elsevier.nlrlocatercplett Electron transfer between adjacent layers in self-assembled films Vitor B.P. Leite a, ) , Marysilvia Ferreira b , Osvaldo N. Oliveira Jr. c a Departamento de Fısica, IBILCE, UniÕersidade Estadual Paulista, Sao J. Rio Preto 15054-000, Brazil ´ ˜ b COPPE, UniÕersidade Federal do Rio de Janeiro, Rio de Janeiro 21945-970, Brazil c Instituto de Fısica de Sao Carlos, UniÕersidade de Sao Paulo, Sao Carlos, Brazil ´ ˜ ˜ ˜ Received 27 September 1999; in final form 18 November 1999 Abstract Ž A simple model of electron transfer is adapted to explain fluorescence quenching in self-assembled films of poly p-phen- .Ž . Ž .Ž . ylene vinylene PPV alternating with poly thiophene acetic acid PTAA . Quenching is caused by a photo-induced Ž . Ž . electron transfer between the excited PPV donor, D and the PTAA acceptor, A . The electron-transfer process can be mediated by insertion of electronically inert spacing bilayers between the D and A layers. As the number of bilayers is increased, the fluorescence is gradually recovered which is explained theoretically by assuming that the electron-transfer rate Ž . can be described as k sZ exp yb r where r is the distance between D and A. q 2000 Elsevier Science B.V. All rights reserved. Luminescence properties in polymeric systems have been extensively investigated in recent years, due to the promising applications of such materials Ž . in light-emitting diodes LED and related electrolu- w x Ž minescent devices 1–5 . The family of poly p- .Ž . phenylene vinylene PPV is prominent among the polymers investigated and has been used in supra- molecular structures fabricated with the Langmuir– Ž . w x Ž Blodgett LB 6,7 or the self-assembly or layer- . w x by-layer 8–11 methods aimed at achieving some degree of molecular control. A clear example of wx molecular control is provided in Ref. 8 where the luminescence of PPV self-assembled films is Ž quenched by alternating PPV with poly thiophene ) Corresponding author. Fax: q55-17-221-2247; e-mail: vleite@df.ibilce.unesp.br .Ž . acetic acid PTAA or sulfonated C . The lumines- 60 cence is gradually recovered as an increasing number of spacer layers are interposed between the PPV and the PTAA or C layers. These results are analyzed 60 in this Letter. The origin of luminescence quenching is well established, but the mechanisms of electron transfer Ž . ET need to be further investigated. A Forster-type energy transfer mechanism can be ruled out since the Ž . required overlap between the donor D emission and Ž . Ž acceptor A absorption bands, in both cases PTAA . or C is not fulfilled. It has been reported that 60 Ž . composites of a PPV derivative MEH–PPV and w x C undergo a photoinduced ET process 12–15 . 60 Evidence for such phenomena relies on the fact that C is a strong electron acceptor. The transfer rate is 60 favorable in the presence of a good donor such as the MEH–PPV. The distance between the donor and 0009-2614r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0009-2614 99 01343-3