Charge transfer in thin films of donor–acceptor complexes studied by infrared spectroscopy

Optical Interference Enhances Nonlinear Spectroscopic Sensitivity: When Light Gives You Lemons, Model Lemonade

“…Work by others had shown linear behavior for vibrational frequencies with fractional charge. 19 As electrons are either added to the anti-bonding LUMO or removed from the HOMO of the PTCDI core, they will affect the frequency of the bond in a proportional way. On initial examination this seems to hold, the nitrile group leads to a fractional charge of -0.0251 and resonance for the carbonyl symmetric stretch of 1696 cm -1 while the more electron donating ethyl group leads to a charge of -0.444 and a frequency 1687 cm -1 .…”

Solution-processed thin films of a charge transfer complex for ambipolar field-effect transistors

“…Using spectroscopic techniques, such as infrared and Raman, it is possible to have a valuable estimation of the ionicity of the CT systems under investigation by looking at the shift of the charge sensitive vibrations. 15,[46][47][48] Regarding the DBTTF-TCNQ system, by Raman spectroscopy it has been reported a degree of ionicity of 0.5 and 0.13 for α and β polymorphs, respectively, using the shift of the totally symmetric a g v 4 mode (C=C stretching) of the acceptor TCNQ as probe of ionicity.…”

“…50 The IR spectrum of the films also show a strong shift of the CN stretching mode which is also a well-known charge sensitive mode. 46 However, the vibration frequency of this functional group can be influenced from the chemical interaction environment due to its position at the edge of the molecular moiety and it is known to give a non-reliable or an overestimation of the ionicity. The entire IR spectrum till 7500 cm -1 is reported in Figure S7 showing the CT band at 5600 cm -1 (~0.7 eV).…”

Diagnosis of the Redox Levels of TCNQF4 Compounds Using Vibrational Spectroscopy

“…With advances in computing power over the last 30 years and the development of fast and accurate density functional (DFT) methods, it is now possible to make far more reliable predictions of IR and Raman spectra. Although DFT studies of TCNQ vibrational spectra have been reported, [13] mixing of d(CÀH) and n(CÀC) in TCNQ mean that it is spectroscopically very different from TCNQF 4 2À , providing both the corresponding symmetry representation and a graphical depiction of each mode. Using these data, we assign the features of the IR and Raman spectra of the three TCNQF 4 species and provide an expanded set of diagnostics for identifying the redox level in compounds where this is unknown.…”