Coordinating Electron Transport Chains to an Electron Donor

Two electron transport chains (<b>2</b> and <b>3</b>) featuring two fullerenes with different electron acceptor strengths have been synthesized, characterized, and coordinated to a light harvesting/electron donating zinc porphyrin. Electrochemical assays corroborate the redox gradients along the designed electron transport chains, and complementary absorption and fluorescence titrations prove the assembly of ZnP-<b>2</b> and ZnP-<b>3</b> hybrids

Efficient Light Harvesters Based on the 10-(1,3-Dithiol-2-ylidene)anthracene Core

Three new push–pull chromophores based on the 10-(1,3-dithiol-2-ylidene)anthracene core were synthesized and fully characterized. The new chromophores display broad absorption spectra, nearly covering the whole visible region, with high extinction coefficients. Electrochemistry and theoretical calculations allowed the understanding of these singular electronic properties. The molecular structures were unambiguously confirmed by X-ray diffraction

Efficient Light Harvesters Based on the 10-(1,3-Dithiol-2-ylidene)anthracene Core

Three new push–pull chromophores based on the 10-(1,3-dithiol-2-ylidene)anthracene core were synthesized and fully characterized. The new chromophores display broad absorption spectra, nearly covering the whole visible region, with high extinction coefficients. Electrochemistry and theoretical calculations allowed the understanding of these singular electronic properties. The molecular structures were unambiguously confirmed by X-ray diffraction

Efficient Light Harvesters Based on the 10-(1,3-Dithiol-2-ylidene)anthracene Core

Three new push–pull chromophores based on the 10-(1,3-dithiol-2-ylidene)anthracene core were synthesized and fully characterized. The new chromophores display broad absorption spectra, nearly covering the whole visible region, with high extinction coefficients. Electrochemistry and theoretical calculations allowed the understanding of these singular electronic properties. The molecular structures were unambiguously confirmed by X-ray diffraction

Efficient Light Harvesters Based on the 10-(1,3-Dithiol-2-ylidene)anthracene Core

Three new push–pull chromophores based on the 10-(1,3-dithiol-2-ylidene)anthracene core were synthesized and fully characterized. The new chromophores display broad absorption spectra, nearly covering the whole visible region, with high extinction coefficients. Electrochemistry and theoretical calculations allowed the understanding of these singular electronic properties. The molecular structures were unambiguously confirmed by X-ray diffraction

Mediating Reductive Charge Shift Reactions in Electron Transport Chains

We report the synthesis of a full-fledged family of covalent electron donor–acceptor₁–acceptor₂ conjugates and their charge-transfer characterization by means of advanced photophysical assays. By virtue of variable excited state energies and electron donor strengths, either Zn­(II)­Porphyrins or Zn­(II)­Phthalocyanines were linked to different electron-transport chains featuring pairs of electron accepting fullerenes, that is, C₆₀ and C₇₀. In this way, a fine-tuned redox gradient is established to power a unidirectional, long-range charge transport from the excited-state electron donor via a transient C₆₀^•– toward C₇₀^•–. This strategy helps minimize energy losses in the reductive, short-range charge shift from C₆₀ to C₇₀. At the forefront of our investigations are excited-state dynamics deduced from femtosecond transient absorption spectroscopic measurements and subsequent computational deconvolution of the transient absorption spectra. These provide evidence for cascades of short-range charge-transfer processes, including reductive charge shift reactions between the two electron-accepting fullerenes, and for kinetics that are influenced by the nature and length of the respective spacer. Of key importance is the postulate of a mediating state in the charge-shift reaction at weak electronic couplings. Our results point to an intimate relationship between triplet–triplet energy transfer and charge transfer

Tuning the Electronic Properties of Nonplanar exTTF-Based Push–Pull Chromophores by Aryl Substitution

A new family of π-extended tetrathiafulvalene (exTTF) donor–acceptor chromophores has been synthesized by [2 + 2] cycloaddition of TCNE with exTTF-substituted alkynes and subsequent cycloreversion. X-ray data and theoretical calculations, performed at the B3LYP/6-31G** level, show that the new chromophores exhibit highly distorted nonplanar molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) units. The electronic and optical properties, investigated by UV/vis spectroscopy and electrochemical measurements, are significantly modified when the TCBD acceptor unit is substituted with a donor phenyl group, which increases the twisting of the TCBD units and reduces the conjugation between the two dicyanovinyl subunits. The introduction of phenyl substituents hampers the oxidation and reduction processes and, at the same time, largely increases the optical band gap. An effective electronic communication between the donor and acceptor units, although limited by the distorted molecular geometry, is evidenced both in the ground and in the excited electronic states. The electronic absorption spectra are characterized by low- to medium-intense charge-transfer bands that extend to the near-infrared

Tuning the Electronic Properties of Nonplanar exTTF-Based Push–Pull Chromophores by Aryl Substitution

A new family of π-extended tetrathiafulvalene (exTTF) donor–acceptor chromophores has been synthesized by [2 + 2] cycloaddition of TCNE with exTTF-substituted alkynes and subsequent cycloreversion. X-ray data and theoretical calculations, performed at the B3LYP/6-31G** level, show that the new chromophores exhibit highly distorted nonplanar molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) units. The electronic and optical properties, investigated by UV/vis spectroscopy and electrochemical measurements, are significantly modified when the TCBD acceptor unit is substituted with a donor phenyl group, which increases the twisting of the TCBD units and reduces the conjugation between the two dicyanovinyl subunits. The introduction of phenyl substituents hampers the oxidation and reduction processes and, at the same time, largely increases the optical band gap. An effective electronic communication between the donor and acceptor units, although limited by the distorted molecular geometry, is evidenced both in the ground and in the excited electronic states. The electronic absorption spectra are characterized by low- to medium-intense charge-transfer bands that extend to the near-infrared

Co-Solvent Effect in the Processing of the Perovskite:Fullerene Blend Films for Electron Transport Layer-Free Solar Cells

An understanding of the improvements achieved in the use of cosolvents for methylammonium lead triiodide (MAPbI₃):C₇₀ blend films (MAPbI₃:C₇₀) processing is presented. A comparative study using aromatic (i.e., <i>o</i>-xylene and <i>o</i>-dichlorobenzene) and aliphatic (i.e., methylcyclohexane and chlorocyclohexane) cosolvents proves the nature of the cosolvent interacting with fullerene to be determining for achieving enhanced devices. UV–vis spectra of the different C₇₀ solutions suggest a major impact of the solute–aromatic solvent interactions on the optoelectronic properties. The effect of aromatic and aliphatic solvents in the electronic structure of C₇₀ crystals, obtained from the different solutions, is indeed demonstrated by electron energy loss spectroscopy. Morphological studies show elimination of pinholes (field emission scanning electron microscopy) and different nanometric features related to fullerene (atomic force microscopy) in MAPbI₃:C₇₀ blend films processed using aromatic cosolvents. A severe quenching of the perovskite emission is observed, suggesting that electron transfer happens from MAPbI₃ to C₇₀ in the MAPbI₃:C₇₀ blend films. Furthermore, a faster charge transfer seems to occur in blend films processed using aromatic cosolvents

Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide

Formamidinium lead triiodide (FAPbI3) is the leading candidate for single-junction metal–halide perovskite photovoltaics, despite the metastability of this phase. To enhance its ambient-phase stability and produce world-record photovoltaic efficiencies, methylenediammonium dichloride (MDACl2) has been used as an additive in FAPbI3. MDA2+ has been reported as incorporated into the perovskite lattice alongside Cl–. However, the precise function and role of MDA2+ remain uncertain. Here, we grow FAPbI3 single crystals from a solution containing MDACl2 (FAPbI3-M). We demonstrate that FAPbI3-M crystals are stable against transformation to the photoinactive δ-phase for more than one year under ambient conditions. Critically, we reveal that MDA2+ is not the direct cause of the enhanced material stability. Instead, MDA2+ degrades rapidly to produce ammonium and methaniminium, which subsequently oligomerizes to yield hexamethylenetetramine (HMTA). FAPbI3 crystals grown from a solution containing HMTA (FAPbI3-H) replicate the enhanced α-phase stability of FAPbI3-M. However, we further determine that HMTA is unstable in the perovskite precursor solution, where reaction with FA+ is possible, leading instead to the formation of tetrahydrotriazinium (THTZ-H+). By a combination of liquid- and solid-state NMR techniques, we show that THTZ-H+ is selectively incorporated into the bulk of both FAPbI3-M and FAPbI3-H at ∼0.5 mol % and infer that this addition is responsible for the improved α-phase stability