Extended Acceptor Systems Observation of Photoinduced Electron Transfer

2 tt-EXTENDED acceptor SYSTEMS OBSERVATION OF PHOTOINDUCED ELECTRON TRANSFER 

One of the most interesting aspects in the synthesis of tetracyano-/ -quinodimethanes other than TCNQ was the increase in the 7r-extension of the electron acceptors. From theoretical calculations Garito and Heeger concluded, 20 years ago, that an extension of the TT-system in such compounds would lead to a 

From previous studies [87,88] it is known that the excess electron density in the TCNQ anions is located at the dicyanomethylene groups. Consequently, the first syntheses of 7r-extended systems were carried out on different polycyclic hydrocarbon skeletons bearing the dicyanomethylene units on the terminal positions. Thus, during the 1970s and early 1980s, novel acceptor structures such as 9,9,10,10-tetracyanonaphtho- 

6-quinodimethane (TNAP) [89,90], 7,7,7, 7 -tetra-cyanodipheno-4,4 -quinodimethane (TCNDQ) [91,92], 11,1 l,12,12-tetracyano-4,5,9,10-tetrahydropyreno-2,7-quinodimethane (TCNTHPQ) [92,93] and 11,11,12,12-tetracyanopyreno-2,7-quinodimethane (TCNPQ) [94] were prepared. 

However, some of these novel acceptors were not stable enough compounds, and although some CT complexes have been described [92,93,95,96], little solid-state data have been reported, due to their large molecular size, to form stable crystalline complexes. Thus, this approach was not as successful as it was initially expected to be. 

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