Formation and Characterization of the π-Radical Cation and Dication of π-Extended Tetrathiafulvalene Materials

Abstract

The π-radical cation as well as the dication species of a series of quinonoid π -extended TTF have been generated by means of time-resolved and steady-state radiation chemical techniques. The spectral characteristics of the π-radical cation revealed fingerprint absorptions, which are predominantly in the red region of the spectrum (570−690 nm). The maxima vary markedly upon altering (i) the substitution pattern of the TTF rings (i.e., H, S−CH3 and S−CH2−CH2−S) and (ii) the different backbone structures (i.e., anthracene, tetracene, and pentacene). In accordance with the electrochemical studies, which give rise to a single two-electron oxidation step forming directly the π -extended TTF dication, the π-radical cation intermediate is short-lived and decays on a time scale of several tens of milliseconds. Clean second-order decay dynamics, indicative for a disproportionation reaction of the π-radical cation into the corresponding dications, govern the instability of the π-radical cation. By contrast the dication species is stable without showing a significant degradation over minutes. All the generated dications show transitions that are significantly shifted to the blue (455−490 nm) relative to the π-radical cation intermediates and are dominated by the polyacenic unit.

Controlling the crystalline three-dimensional order in bulk materials by single-wall carbon nanotubes

“…In the visible, the newly formed transient is characterized by a broad maximum at 680 nm. The latter resembles the radiolytically and photolytically generated fingerprint of the one electron-oxidized radical cation of exTTF 53,54 . In the NIR, appreciable blue shifts of the transient bleaching are detected, with minima that shift from 1,040 and 1,145 nm to 1,010 and 1,135 nm, respectively, followed by a broad transient between 1,150 and 1,600 nm.…”

Control over Electron Transfer in Tetrathiafulvalene‐Modified Single‐Walled Carbon Nanotubes

“…In stark contrast, nanosecond excitation of fine dispersions of SWNT-TTF and SWNT-exTTF in THF gave rise in the visible range (Figure 4) to the well-known signatures, namely, transitions at 440 nm and 660 nm, respectively, of the TTF and exTTF radical cations. [15] To gather evidence for the reduction of the SWNTs we examined the near-infrared region of the spectrum. In this region, the radical cation absorptions of the donor fragments are negligible and the van Hove singularities of the SWNTs constitute the major absorbing species.…”

Electron Donor–Acceptor Interactions in Regioselectively Synthesized exTTF2–C70(CF3)10 Dyads

“…Spectral characteristics of this very short-lived excited state (1.2 ps) are transient maxima around 465, 605, and 990 nm, as well as a transient minimum at 440 nm. [28] The short lifetimes (i.e., after 5 ps no transient absorption remains) are rationalized by the presence of the sulfur atoms, with a strong second-order vibronic spin-orbit coupling. [29] On the other hand, the differential spectra recorded immediately after the laser pulse for C 1 -C 70 A C H T U N G T R E N N U N G (CF 3 ) 10 in 1 and 2 are characterized, for example, in the near-infrared by a broad absorption with its maximum at 1050 nm.…”

“…Regarding the femtosecond transient absorption measurements of 4, immediately after the laser excitation, the strong singlet-singlet absorptions of exTTF (i.e., maxima at 465, 605, and 990 nm; minimum at 440 nm) [28] and C 1 -C 70 A C H T U N G T R E N N U N G (CF 3 ) 10 (i.e., maximum at 1050 nm) [30] start to grow, (about 1 10 12 s…”

“…Spectroscopic proof for the radical-ion pair formation was obtained from the features developing in parallel with the disappearance of the exTTF and C 1 -C 70 A C H T U N G T R E N N U N G (CF 3 ) 10 singlet-singlet absorption, which are exemplified in Figures 10 and 11. In the visible region, a set of two maxima at 610 and 660 nm corresponds to the one-electron oxidized exTTFC + , [28] whereas in the near-infrared region the 1450 nm maximum resembles the signature of the one-electron reduced C 1 -C 70 A C H T U N G T R E N N U N G (CF 3 ) 10 C À . [32] In THF and benzonitrile, the www.chemeurj.org same radical-ion pair state features were seen to be formed.…”