N-docosylpyridinium-TCNQ

Construction of LB films having lateral d.c. conductivities is a burgeoning activity. Results of published work are summarized in Table 9 [726-772]. The first formation of a conducting LB film was reported by French workers in 1985 [726]. Non-conducting LB films were formed from N-docosylpyridinium TCNQ. Subsequent exposure to iodine vapor resulted, however, in the lateral conductivities in the order of 0.1 S cm-1 [726]. The initially formed LB film was shown to consist of (TCNQ. )2 dimers whose molecular planes were almost parallel to the substrate. Iodination resulted in the development of a brown-purple color, the partial oxidization erf the radical anions to TCNQ° and, most importantly, a dramatic rearrangement of the LB film. In iodine-doped films, the TCNQ molecules have been shown to assume a position almost perpendicular to the substrate [721, 773],... 

LB films prepared from N-docosylpyridinium (TCNQ)2 and transferred to substrates Absorption and infrared spectra Lateral d.c. conductivity was determined to be 10"2 Scm"1, even without iodine doping 739, 740... 

Tetracyanoquinodimethane (TCNQ) (30) is well known for its use in charge-transfer salts, and has been reported to produce good conduction behaviour in LB films when deposited in alternate layers with N-octadecylpyridinium salts (29) (with n = 18). TCNQ has also been used for homodoped LB films wherein two derivatives of the same electroactive nucleus are used to form mixed surface monolayers suitable for LB deposition. Conductivity values of 0.2 Sm have been obtained when using mixed monolayers of octadecyl-substituted TCNQ (34), with N-docosylpyridinium TCNQ (29) (with n = 22) in a ratio of 1 3 [54]. 

As the monovalent TCNQ salt should be insulating, a certain degree of oxidation of TCNQ" may occur during the film deposition process, which was confirmed by XPS investigations [54]. A similar oxidation can also take place in the case of N-docosylpyridinium-TCNQ [55]. 

Langmuir-Blodgett (LB) films prepared from N-docosylpyridinium and TCNQ, transferred to substrates, and exposed to iodine vapor Visible and infrared spectra and low-angle X-ray diffraction Lateral d.c, conductivity was about lO- Scm 1 726, 729... 

Figure 14.13. n-A and a-A isotherms of (1) V-docosylpyridinium-TCNQ and (2) V-docosylpyridinium-(TCNQ)2 at the air-glycerine interface. (Reproduced by permission of Elsevier Science S.A. from ref 68.)... 

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