Effects of Acceptor Modification on Charge Transfer in Crystals of Donor‐Acceptor Systems of TTF

Abstract

The degree of charge transfer has been determined in six TTF-fluorene derivative charge trans fer complexes, using IR and Raman vibrational spectroscopies. It has been found that changes of the intermolecular electronic distribution is strongly influenced by the presence of the dicyanomethylene group, by the increase of the nitro groups, as well as by the symmetry of the acceptor.

Caractérisation structurale et étude spectroscopique du transfert de charge pour deux phases polymorphes du complexe (TTF)3(TNF)2, avec TTF = tétrathiofulvalène et TNF = 2,4,7-trinitro-9-fluorénone

“…Dans le cas qui nous occupe, le transfert de charge est probablement de faible intensité. En effet, pour un complexe TTF-TNF, dont la structure cristalline n'est pas connue, d a été évalué sur la base de spectres Raman : d ≈ 0,05 [32]. Par ailleurs, les séparations D•••A observées dans l'intervalle 3,75-4,17 Å pour (TTF) 3 (TNF) 2 sont relativement grandes comparées, par exemple, à la distance D•••A = 3,74 Å pour le complexe 1:1 construit avec TTF et la 2,7-dinitro-9fluorénone [12], pour lequel d ≈ 0,09 [32].…”

Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex

“…46 However, several vibrational modes are considerably shifted in frequency, and it is well established that these shifts of donor and acceptor frequencies are related to the occurrence of a ground state charge transfer. 48,[50][51][52][53][54] In particular, for the acceptor, TNF, a redshift of the C=O stretching mode has been observed in ground state CT complexes and is related to an increase in the electron density resulting from partial ground-state CT. 48,52 In the HAT6-TNF spectrum, the C=O mode is observed to have redshifted to 1730 cm −1 . Based on the data in literature 52 it is estimated that the shift of 3 cm −1 corresponds to an increase in electron density on TNF of about 0.03 e − .…”

“…48,[50][51][52][53][54] In particular, for the acceptor, TNF, a redshift of the C=O stretching mode has been observed in ground state CT complexes and is related to an increase in the electron density resulting from partial ground-state CT. 48,52 In the HAT6-TNF spectrum, the C=O mode is observed to have redshifted to 1730 cm −1 . Based on the data in literature 52 it is estimated that the shift of 3 cm −1 corresponds to an increase in electron density on TNF of about 0.03 e − . In addition, for all the assigned modes we found satisfactory agreement between the observed shifts and normalized frequency changes between neutral TNF and the anion TNF −1 calculated with DFT (Table S4), with the normalization factor corresponding to a ground state charge transfer of about 0.06 electron.…”