X-Ray Photoelectron Spectroscopic Study of Tetrathiafulvalene–Tetracyanoquinodimethane (TTF·TCNQ) and Related High Conductive Organic Complexes

Tetrathiafulvalene–tetracyanoquinodimethane (TTF·TCNQ) and related high conductive organic complexes were studied by X-ray photoelectron spectroscopy (XPS). The N 1s peak shape of TTF·TCNQ evaporated film was found to change by X-ray irradiation; the high-binding energy shoulder of the N 1s peak increased its intensity with X-ray irradiation time and finally showed a new peak separated by about 1.5 eV from the main peak. TTF·TCNQ was found to be 1:1 both in the surface and in the bulk. The amounts of charge transfer in TTF·TCNQ and other TTF complexes as well as those in 5,6:11,12-bis(dithio)naphthacene(tetrathiotetracene, TTT) complexes were determined from the analysis of the S 2p peak shape. The amount of charge transfer is 0.56±0.05 in TTF·TCNQ and 0.55±0.05 in TTF·TNAP (tetracyanonaphthoquinodimethane). The molecular ratio of (donor)+ in donor molecules is 0.71±0.05 in TTF·Br0.7, 0.52±0.05 in TTF·I0.7, 0.65±0.05 in (TTF)3(BF4)2, 0.49±0.05 in (TTT)2I3, and 0.93±0.05 in (TTT)(TCNQ)2, which correspond respectively to 100, 73, 100, 100, and 100% charge transfer between donors and acceptors. The N 1s peak shape of TTF·TCNQ is also discussed.