INFRARED AND RAMAN-STUDY OF POLYANILINE .2. INFLUENCE OF ORTHO SUBSTITUENTS ON HYDROGEN-BONDING AND UV VIS NEAR-IR ELECTRON CHARGE-TRANSFER/

IR and Raman spectra of chemically (electrochemically) prepared proton ated forms of polymers of 2-methyl (PANIME), 2-methoxy (PANIMEO), 2-ch loro (PANICL) and 2-fluoroanilines (PANIF) and their corresponding bas es have been investigated in the 4000-100(200)cm(-1) region. Exciting lines at 457.94, 514.53, 632.81 and 1064nm have been used for the inve stigation of Raman resonance spectra in order to characterize the benz enoid and (semi)quinoid (SQ) parts of the repeat unit. Highly conducti ng poly-2-methyl and poly-2-methoxyaniline on the one hand show spectr al features which can be interpreted in terms of a strong N-H ... N hy drogen bond (d(N-N)approximate to 0.25nm) with a NH stretching broad a bsorption centred near 1300 cm(-1) cut by numerous Evans transmission bands. On the other hand, poly-2-chloro and poly-2-fluoroaniline which have much lower conductivity have much weaker N-H ... X hydrogen bond s characterized by NH stretching bands near 3000cm(-1) (d(N-N)approxim ate to 0.28/0.285nm). Conductivity mechanisms are discussed. UV/Vis-IR spectra show that conductivity is essentially associated with interch ain coupling. IR spectra suggest that in PANIME and PANIMEO as in PANI the interchain charge carriers constitute bipolaronic species, i.e. - NH+=SQ=NH+-, cross-linked by NK ... N hydrogen bonds. In weakly conduc ting PANIF and PANICL, however, disproportionation of the bipolaronic species, no longer stabilized by H-bonding, leads to localized polaron ic moieties. Possible mechanisms for proton conduction are discussed.