In-situ generation and analysis of charge transfer materials using an OTTLE cell and resonance Raman scattering

Poly(aryl)amine based charge transfer materials (CTMs) are essential components in a range of present and future technologies, from the Xerox process to display devices based upon light emitting polymers (LEPs). However. there is a lack of detailed understanding regarding the electronic properties of CTMs in their various neutral and oxidized forms. This paper reports the use of an optically transparent thin layer electrochemical (OTTLE) cell in combination with a Raman microprobe system and DFT calculations to provide information on the molecular and electronic structure of the mono- and di-oxidized derivatives of the classic CTM N,N'-diphenyl-N,N''-bis (3-methylphenyl)(1,1'-biphenyl)-4,4'-diamine (TPD) and the closely related species N,N'-diphenyl-N,N'-bis(2,4-dimethylphenyl)(1,1'-biphenyl)-4,4'-diamine (DMTPD). The resonance Raman scattering profile easily discriminates between the monovalent and divalent cations while DFT calculations permit correlation of the observed vibrational frequencies with localized atomic displacements. The cations are best described in terms of a symmetrical (i.e. fully delocalized) structure. The high sensitivity of the method suggests that it should be appropriate for the observation of low concentrations of the various cations generated from TPD type CTMs during device operation.