Photoinduced Electron-Transfer Processes of Tetrathiafulvalene-(Spacer)-(Naphthalenediimide)-(Spacer)-Tertrathiafulvalene Triads in Solution

Donor-Donor'-Acceptor Triads Based on [3.3]Paracyclophane with a 1,4-Dithiafulvene Donor and a Cyanomethylene Acceptor: Synthesis, Structure, and Electrochemical and Photophysical Properties

Donor-donor'-acceptor triads (1, 2), based on [3.3]paracyclophane ([3.3]PCP) as a bridge, with electron-donating properties (D') using 1,4-dithiafulvene (DTF; TTF half unit) as a donor and dicyanomethylene (DCM; TCNE half unit) or an ethoxycarbonyl-cyanomethylene (ECM) as an acceptor were designed and synthesized. The pulse radiolysis study of 1 a in 1,2-dichloroethane allowed the clear assignment of the absorption bands of the DTF radical cation (1 a^.+ ), whereas the absorption bands due to the DCM radical anion could not be observed by γ-ray radiolysis in 2-methyltetrahydrofuran rigid glass at 77 K. Electrochemical oxidation of 1 a first generates the DTF radical cation (1 a^.+ ), the absorption bands of which are in agreement with those observed by a pulse radiolysis study, followed by dication (1 a²⁺ ). The ESR spectrum of 1 a^.+ showed a symmetrical signal with fine structure and an ESR simulation predicted that the spin of 1 a^.+ is delocalized over S and C atoms of the DTF moiety and the central C atom of the trimethylene bridge bearing the DTF moiety. Pulse radiolysis, ESR, and electrochemical studies indicate that the DTF radical cation of 1 a^.+ is more stable than that of 6^.+ , and the latter shows a strong tendency to dimerize. This result indicates that the [3.3]PCP moiety as a bridge can stabilize the DTF radical cation more than the 1,3-diphenylpropane moiety because of kinetic stability due to its rigid structure and the weak electronic interaction of DTF and DCM moieties through [3.3]PCP.

Comparison of 3D non-fullerene acceptors for organic photovoltaics based on naphthalene diimide and perylene diimide-substituted 9,9′-bifluorenylidene

Tetra(PDI) derivatives of non-planar cores have previously been used as acceptors in OPVs; here a tetra(NDI) is shown to be a viable alternative, although, for the pair of acceptors and the donor polymers used here, the PDI species performs better.

Ultrafast Intersystem-Crossing Dynamics and Breakdown of the Kasha-Vavilov's Rule of Naphthalenediimides

The fluorescence quantum yield of a red naphthalenediimide dye (rNDI) with amino and Br core substituents has been found to decrease by a factor of almost 2 by going from S1 ← S0 to S2 ← S0 excitation. Time-resolved spectroscopic measurements reveal that this deviation from the Kasha-Vavilov's rule is due to an ultrafast, < 200 fs, intersystem-crossing (ISC) from the S2 state to the triplet manifold, due to the ππ* → nπ* character of the transition and to the presence of the heavy Br atom. In non-core substituted naphthalenediimide (pNDI), ISC is slower, ∼2 ps, and was found to be reversible on a time scale shorter than that of vibrational cooling. The fluorescence and triplet quantum yields of rNDI, thus, can be substantially changed by a simple variation of the excitation wavelength.

Self-assembly of a dendron-attached tetrathiafulvalene: gel formation and modulation in the presence of chloranil and metal ions

The self-assembly of a tetrathiafulvalene (TTF)-based molecular gelator with a dendron substituent into a gel is described. Scanning electron microscope and atomic force microscope studies show that the xerogels exhibit rope-like frameworks or interwoven nanofibers, depending on the polarity of solvent from which the gel is formed. Gels containing chloranil can also be successfully prepared. Interestingly, this two-component gel can be easily transformed into solution after the addition of either Sc³⁺ or Pb²⁺. Both absorption and electron spin resonance (ESR) spectroscopic investigations reveal that the TTF unit is oxidized into TTF+ by chloranil in the presence of either Sc³⁺ or Pb²⁺. Moreover, the gel phase can be restored by reduction of TTF+ into the neutral form using magnesium.

New substituted tetrathiafulvalene-quinone dyads: the influences of electron accepting abilities of quinone units on the metal ion-promoted electron-transfer processes

The metal ion-promoted electron transfer occurs to all new dyads 1, 2, 3, and 4, even one of them, dyad 4, which has a rather weak electron acceptor unit. The results also indicate that the metal ion-promoted electron transfer within the dyads is influenced by the electron accepting abilities of quinone units; dyad 2 with the strongest electron acceptor among the four dyads shows the strongest absorption and ESR signals attributed to TTF.+ in the presence of metal ions.

Metallomacrocycles That Incorporate Cofacially Aligned Diimide Units

Pyromellitic diimide and naphthalene diimide moieties were incorporated into hemilabile phosphanylalkyl thioether ligands. These ligands reacted with [Cu(CH3CN)4]PF6 and [Rh(NBD)Cl]2 (NBD = norbornadiene) by the weak-link approach to form condensed intermediates. Upon reaction of each diimide ligand with these transition-metal precursors, the two diimide units became cofacially aligned within a supramolecular macrocyclic architecture. The introduction of ancillary ligands to each of these condensed intermediates caused the weak thioether-metal bonds to break, thus generating a large macrocycle in which the distance between diimide units is significantly larger than for the condensed intermediates. The two Rh(I) cationic condensed intermediates were characterized by single-crystal X-ray diffraction studies, and the electrochemical activity of these macrocycles was demonstrated with the naphthalene diimide-Cu(I) macrocycles.

Photoinduced Intramolecular Electron-Transfer Processes in [60]Fullerene and N,N-Bis(biphenyl)aniline Molecular Systems in Solutions

Photoinduced intramolecular charge-separation and charge-recombination processes in covalently connected C(60)-(spacer)-bis(biphenyl)aniline (C(60)-sp-BBA) and C(60)-((spacer)-bis(biphenyl)aniline)(2) (C(60)-(sp-BBA)(2)) have been studied by time-resolved fluorescence and transient absorption methods. Since a flexible alkylthioacetoamide chain was employed as the spacer, the folded structures in which the BBA moiety approaches the C(60) moiety were obtained as optimized structures by molecular orbital calculations. The observed low fluorescence intensity and the short fluorescence lifetime of the C(60) moiety of these molecular systems indicated that charge separation takes place via the excited singlet state of the C(60) moiety in a quite fast rate and high efficiency even in the nonpolar solvent toluene, which was a quite new observation compared with reported dyads with different spacers. From the absorption bands at 880 and 1000 nm in the nanosecond transient absorption spectra, generations of C(60)(.-)-sp-BBA(.+) and C(60)(.-)-(sp-BBA(.+))(sp-BBA) were confirmed. The rates of charge separation and charge recombination for C(60)-(sp-BBA)(2) are faster than those for C(60)-sp-BBA, suggesting that one of the BBA moieties approaches the C(60) moiety by pushing another BBA moiety because of the flexible spacers.

Misleading effects of impurities derived from the extremely long-lived electron-transfer state of 9-mesityl-10-methylacridinium ion

9-Mesityl-10-methylacridinium ion has an extremely long-lived electron-transfer state, which results in the misleading effects of electron donor impurities contained in benzonitrile to produce the stable acridinyl radical.