Structure and photophysics of indigoids for singlet fission: Cibalackrot

We report an investigation of structure and photophysics of thin layers of cibalackrot, a sturdy dye derived from indigo by double annulation at the central double bond. Evaporated layers contain up to three phases, two crystalline and one amorphous. Relative amounts of all three have been determined by a combination of X-ray diffraction and FT-IR reflectance spectroscopy. Initially, excited singlet state rapidly produces a high yield of a transient intermediate whose spectral properties are compatible with charge-transfer nature. This intermediate more slowly converts to a significant yield of triplet, which, however, does not exceed 100% and may well be produced by intersystem crossing rather than singlet fission. The yields were determined by transient absorption spectroscopy and corrected for effects of partial sample alignment by a simple generally applicable procedure. Formation of excimers was also observed. In order to obtain guidance for improving molecular packing by a minor structural modification, calculations by a simplified frontier orbital method were used to find all local maxima of singlet fission rate as a function of geometry of a molecular pair. The method was tested at 48 maxima by comparison with the ab initio Frenkel-Davydov exciton model. Published under license by AIP Publishing

Singlet Fission and Excimer Formation in Disordered Solids of Alkyl-Substituted 1,3-Diphenylisobenzofurans

We describe the preparation and excited state dynamics of three alkyl derivatives of 1,3-diphenylisobenzofuran (<b>1</b>) in both solutions and thin films. The substitutions are intended to disrupt the slip-stacked packing observed in crystals of <b>1</b> while maintaining the favorable energies of singlet and triplet for singlet fission (SF). All substitutions result in films that are largely amorphous as judged by the absence of strong X-ray diffraction peaks. The films of <b>1</b> carrying a methyl in the para position of one phenyl ring undergo SF relatively efficiently (≥75% triplet yield, Φ_T) but more slowly than thin films of <b>1</b>. When the methyl is replaced with a <i>t</i>-butyl, kinetic competition in the excited state favors excimer formation rather than SF (Φ_T = 55%). When <i>t</i>-Bu groups are placed in both meta positions of the phenyl substituent, SF is slowed further and Φ_T = 35%

Structure of a monolayer of molecular rotors on aqueous subphase from grazing-incidence X-ray diffraction.

In situ grazing-incidence X-ray scattering shows that a monolayer of artificial rod-shaped dipolar molecular rotors produced on the surface of an aqueous subphase in a Langmuir trough has a structure conducive to a 2D ferroelectric phase. The axes of the rotors stand an average of 0.83 nm apart in a triangular grid, perpendicular to the surface within experimental error. They carry 2,3-dichlorophenylene rotators near rod centers, between two decks of interlocked triptycenes installed axially on the rotor axle. The analysis is based first on simultaneous fitting of observed Bragg rods and second on fitting the reflectivity curve with only three adjustable parameters and the calculated rotor electron density, which also revealed the presence of about seven molecules of water near each rotator. Dependent on preparation conditions, a minor and variable amount of a different crystal phase may also be present in the monolayer

EPR Spectroscopy of Radical Ions of a 2,3-Diamino-1,4-naphthoquinone Derivative

We report the electron paramagnetic resonance spectra of the radical cation and radical anion of 1,2,2,3-tetramethyl-2,3-dihydro-1<i>H</i>-naphtho­[2,3-<i>d</i>]­imidazole-4,9-dione (<b>1</b>) and its doubly ¹³C labeled analogue <b>2</b>, of interest for singlet fission. The hyperfine coupling constants are in excellent agreement with density functional theory calculations and establish the structures beyond doubt. Unlike the radical cation <b>1</b>^<b>•+</b>, the radical anion <b>1</b>^{<b>•–</b>} and its parent <b>1</b> have pyramidalized nitrogen atoms and inequivalent methyl groups 15 and 16, in agreement with the calculations. The distinction is particularly clear with the labeled analogue <b>2</b>^{<b>•–</b>}

A self-assembled bis(pyrrolo)tetrathiafulvalene-based redox active squarew

International audienceThe synthesis and full characterization of a redox-active p-donating molecular square is described, through coordination-driven self-assembly of a new key bis(pyrrolo)TTF building block with Pt(II) salts; the electrochemical behaviour of the square is consistent with noninteracting bis(pyrrolo)TTF units

Self-Assembled Containers Based on Extended Tetrathiafulvalene

Two original self-assembled containers constituted each by six electroactive subunits are described. They are synthesized from a concave tetratopic π-extended tetrathiafulvalene ligand bearing four pyridyl units and <i>cis</i>-M­(dppf)­(OTf)₂ (M = Pd or Pt; dppf = 1,1′-bis­(diphenylphosphino)­ferrocene; OTf = trifluoromethane-sulfonate) complexes. Both fully characterized assemblies present an oblate spheroidal cavity that can incorporate one perylene molecule

Self-Assembled Containers Based on Extended Tetrathiafulvalene

Two original self-assembled containers constituted each by six electroactive subunits are described. They are synthesized from a concave tetratopic π-extended tetrathiafulvalene ligand bearing four pyridyl units and <i>cis</i>-M­(dppf)­(OTf)₂ (M = Pd or Pt; dppf = 1,1′-bis­(diphenylphosphino)­ferrocene; OTf = trifluoromethane-sulfonate) complexes. Both fully characterized assemblies present an oblate spheroidal cavity that can incorporate one perylene molecule

Covalent Dimers of 1,3-Diphenylisobenzofuran for Singlet Fission: Synthesis and Electrochemistry

The synthesis of covalent dimers in which two 1,3-diphenylisobenzofuran units are connected through one phenyl substituent on each is reported. In three of the dimers, the subunits are linked directly, and in three others, they are linked via an alkane chain. A seventh new compound in which two 1,3-diphenylisobenzofuran units share a phenyl substituent is also described. These materials are needed for investigations of the singlet fission process, which promises to increase the efficiency of solar cells. The electrochemical oxidation and reduction of the monomer, two previously known dimers, and the seven new compounds have been examined, and reversible redox potentials have been compared with results obtained from density functional theory. Although the overall agreement is satisfactory, some discrepancies are noted and discussed

Self-Assembled Containers Based on Extended Tetrathiafulvalene

Two original self-assembled containers constituted each by six electroactive subunits are described. They are synthesized from a concave tetratopic π-extended tetrathiafulvalene ligand bearing four pyridyl units and <i>cis</i>-M­(dppf)­(OTf)₂ (M = Pd or Pt; dppf = 1,1′-bis­(diphenylphosphino)­ferrocene; OTf = trifluoromethane-sulfonate) complexes. Both fully characterized assemblies present an oblate spheroidal cavity that can incorporate one perylene molecule

Covalent Dimers of 1,3-Diphenylisobenzofuran for Singlet Fission: Synthesis and Electrochemistry

The synthesis of covalent dimers in which two 1,3-diphenylisobenzofuran units are connected through one phenyl substituent on each is reported. In three of the dimers, the subunits are linked directly, and in three others, they are linked via an alkane chain. A seventh new compound in which two 1,3-diphenylisobenzofuran units share a phenyl substituent is also described. These materials are needed for investigations of the singlet fission process, which promises to increase the efficiency of solar cells. The electrochemical oxidation and reduction of the monomer, two previously known dimers, and the seven new compounds have been examined, and reversible redox potentials have been compared with results obtained from density functional theory. Although the overall agreement is satisfactory, some discrepancies are noted and discussed