Extended TCNQ derivatives as acceptors in composite films with photoinduced electron transfer

4 Extended TCNQ derivatives as acceptors in composite films with photoinduced electron transfer 

Interesting photoinduced electron-transfer reactions in mixed films of r-conjugated polymers and a homologous series of tetracyano-p-quinodimethane (TCNQ) derivatives have been recently reported [135]. Photoinduced absorption (PIA) and photoluminescence experiments have been carried out to study the photoexcitation of poly[2-methoxy-5-(2 -ethylhexy-loxy)-l,4-phenylenevinylene] (MEH-PPV) [136] and poly[3-(2-(3-methylbutoxy)ethyl)thiophene] 

TCNQ and TCAQ acceptors exhibit a significantly lower rate of photoinduced electron transfer, despite the fact that they are better acceptors than TCTQ, 5,14-TCPQ and Ceo- A qualitative interpretation for such behaviour was predicted from the Marcus theory for electron transfer and referred to as the inverted region [139]. On the other hand, the efficient photoinduced charge transfer of MEH-PPV in combination with acceptors TCTQ, diMeO-TCTQ, 5,14-TCPQ and C6o, compared with the lack of activity for 1,4-benzoqui-nones with a similar reduction potential value, indicates that the reduction potential is not the only parameter that affects the electron-transfer rate. Nevertheless, phase segregation and the solubility of the acceptors within the conjugated polymer might make difficult the interpretation of the observed results [135]. 

3 ELECTRON-TRANSFER PROCESSES IN DONOR-ACCEPTOR SYSTEMS 

The interest of electron transfer reactions in many areas of science was recently remarked by Rudolph A. Marcus in his lecture on the occasion of the presentation of the Nobel Prize in Chemistry in 1992 [140]. In particular, electron transfer played an important role in chemical and biological reactions and thus, different types of bridge donor-acceptor molecules have been prepared in order to study the intramolecular electron-transfer mechanisms [141,142], The design of novel organic molecules containing electron donor (D) and electron acceptor (A) moieties constitutes a promising field of study due to the interesting optical and 

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