Photochemical Generation of Radical Cations of Dithienothiophenes, Condensed Thiophene Trimers, Studied by Laser Flash Photolysis

Abstract

Photoinduced electron-transfer reactions between dithienothiophene (DTT) and the electron acceptors, p-dinitrobenzene (DNB) and CCl4, have been investigated using nanosecond laser flash photolysis and time-resolved fluoresence spectroscopy. Generation of the radical cations of DTTs and radical anion of DNB in acetonitrile solution was confirmed by transient absorption spectra in the visible and near-IR regions. Observed transient absorption bands corresponded to those of radical ions generated by γ irradiation in a frozen matrix. Electron transfer occurred both from the singlet and triplet excited states of DTT to DNB at the diffusion-controlled rate, ∼1010 M-1 s-1. When CCl4 was used as an acceptor, electron transfer from the singlet excited state occurred at the diffusion-controlled rate, while the reaction from the triplet excited state occurred at <109 M-1 s-1 due to small ΔG 0 for this reaction. For both acceptors, the singlet route tended to dominate the triplet route when concentration of the acceptor was increased. The radical ions decayed with second-order kinetics by back-electron transfer at a rate closed to the diffusion-controlled limit. In cyclohexane, generation of radical ions was completely suppressed and the triplet excited state of DTT was deactivated by energy transfer to DNB.

The effects of oxygenation on the optical properties of dimethyl-dithienothiophenes: Comparison between experiments and first-principles calculations

“…[20][21][22][23] The optical properties of oligothiophenes have been studied for a long time and in much detail, but, due to the size of these systems, only with semiempirical methods ͑see, e.g., Refs. 11,[33][34][35][36] Furthermore, in all these studies about oli-a͒ Electronic mail: fabio.dellasala@unile.it gothiophenes and dithienothiophenes, the optical properties have been theoretically studied only in the context of absorption spectra, i.e., by carrying out calculations of excitation energies. Recently, some studies using more accurate ab initio approaches 18,[29][30][31][32] have appeared.…”

Chemical RedOx Properties of a Donor-Acceptor Conjugated Microporous Dithienothiophene-Benzene co-Polymer FormedviaSuzuki-Miyaura Cross-coupling

“…UV/Vis absorption spectra of the pristine, oxidized and reduced states were also recorded to verify DTT‐iodide charge transfer along the polymeric network. A clear change was observed for the oxidized form as an additional strong absorption above 550 nm, corresponding to the formation of the charge‐transfer salt . In more details, the appearance of a peak at 580 nm with a shoulder at 620 nm and a small bathochromic shift of the λ max from 402 nm to 438 nm were monitored for DTT‐CMP‐Sz + ‐I − .…”

Fused Thiophenes and Some Oligomers and Polymers Therefrom

“…DTT 253e, substituted with 2-thienyl, was electro-copolymerized with EDOT on a glassy carbon electrode (GCE) [105,106]. The photochemical polymerization of 242 in the presence of an appropriate electron acceptor such as p-dinitrobenzene (DNB) involves photoinduced electron transfer from the singlet excited state of 242 to the DNB producing a radical cation of 242 and a radical anion of DNB [107,108]. DTT and DTT-S,S-dioxides were copolymerized generating 284 and 286: thien-2-yltributylstannane (281) was cross-coupled with dibromo-DTT (282) or dibromo-DTT-S,S-dioxide (285) to obtain the monomers 283 and 285, respectively.…”