Intramolecular excimer formation between 3,6-Di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione chromophoric groups linked by a flexible alkyl spacer

Bichromophoric molecules containing two 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) moieties linked via aliphatic spacers of different length are synthesized. Optical absorption spectroscopy indicates that the molecules adopt an extended conformation in solution. Fluorescence spectroscopy shows that photons are emitted from the locally excited singlet state in an extended conformation. In sufficiently polar solvents, quenching of fluorescence occurs and fluorescence quantum yield (FF) and fluorescence lifetime (tF) measurements indicate formation of an intramolecular excimer as the quenching mechanism. The redox potentials of the molecules and the solvent polarity dependence of the quenching are consistent with significant charge-transfer character of the excimer state. Photoinduced absorption measurements show enhanced intersystem crossing to the triplet state in polar solvents. Results indicate that in donor–acceptor p-conjugated materials involving the DPP moiety, excimer-like interchain polaron pair excited states could play an important role in the photophysics because of their close proximity in energy to the lowest singlet excited

Intramolecular Excimer Formation between 3,6-Di(thiophen-2-yl)pyrrolo[3,4‑<i>c</i>]pyrrole-1,4(2<i>H</i>,5<i>H</i>)‑dione Chromophoric Groups Linked by a Flexible Alkyl Spacer

Bichromophoric molecules containing two 3,6-di­(thiophen-2-yl)­pyrrolo­[3,4-<i>c</i>]­pyrrole-1,4­(2<i>H</i>,5<i>H</i>)-dione (DPP) moieties linked via aliphatic spacers of different length are synthesized. Optical absorption spectroscopy indicates that the molecules adopt an extended conformation in solution. Fluorescence spectroscopy shows that photons are emitted from the locally excited singlet state in an extended conformation. In sufficiently polar solvents, quenching of fluorescence occurs and fluorescence quantum yield (Φ_F) and fluorescence lifetime (τ_F) measurements indicate formation of an intramolecular excimer as the quenching mechanism. The redox potentials of the molecules and the solvent polarity dependence of the quenching are consistent with significant charge-transfer character of the excimer state. Photoinduced absorption measurements show enhanced intersystem crossing to the triplet state in polar solvents. Results indicate that in donor–acceptor π-conjugated materials involving the DPP moiety, excimer-like interchain polaron pair excited states could play an important role in the photophysics because of their close proximity in energy to the lowest singlet excited state

Photophysics of Self-Assembled Monolayers of a π-Conjugated Quinquethiophene Derivative

The photophysics of fully and partially covered self-assembled monolayers (SAMs) of a quinquethiophene (5T) derivative have been investigated. The monolayers behave as H-aggregates. The fluorescence of fully covered SAMs is weak and red-shifted, and the extinction is blue-shifted as compared to that of single molecules. The fluorescence of partially covered SAMs is dominated by that of single molecules on the surface. The extinction spectra are similar for fully and partially covered monolayers, which show that even the smallest islands are H-aggregates. The extinction spectra furthermore closely resemble those for 5T single crystals, which demonstrates that in oligothiophene crystals the intermolecular interactions within one layer molecules are stronger than the interlayer electronic coupling.

Synthesis and optical properties of Pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione (iDPP)-based molecules

We describe the synthesis and photophysical properties of a series of derivatives of pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione-3,6-diyl (iDPP) linked to two oligothiophenes of variable length (nT). The iso-DPP-oligothiophenes (iDPPnTs) differ from the common pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl-oligothiophene analogues (DPPnTs) by a different orientation of the two lactam rings in the bicyclic iDPP unit compared to DPP. In contrast to the highly fluorescent DPPnTs, the new isomeric iDPPnTs exhibit only very weak fluorescence. We demonstrate with the help of quantum-chemical calculations that this can be attributed to a different symmetry of the lowest excited state in iDPPnT (A in C2 symmetry) compared to DPPnTs (B) and the corresponding loss in oscillator strength of the lowest energy transition. Upon extending the oligothiophene moiety in the iDPPnTs molecules, the charge transfer character of the lowest A excited state becomes more pronounced. This tends to preclude high fluorescence quantum yields even in extended iDPPnTs systems

High mobility, hole transport materials for highly efficient PEDOT:PSS replacement in inverted perovskite solar cells

© 2017 The Royal Society of Chemistry. Perovskite solar cells are one of the most promising photovoltaic technologies due to their rapid increase in power conversion efficiency (3.8% to 21.1%) in a very short period of time and the relative ease of their fabrication compared to traditional inorganic solar cells. One of the drawbacks of perovskite solar cells is their limited stability in non-inert atmospheres. In the inverted device configuration this lack of stability can be attributed to the inclusion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the hole transporting layer. Herein we report the synthesis of two new triarylamine based hole transporting materials, synthesised from readily available starting materials. These new materials show increased power conversion efficiencies, of 13.0% and 12.1%, compared to PEDOT:PSS (10.9%) and exhibit increased stability achieving lifetimes in excess of 500 hours. Both molecules are solution processible at low temperatures and show potential for low cost, scalable production of large scale perovskite solar cells on flexible substrates

One-Step Facile Synthesis of a Simple Hole Transport Material for Efficient Perovskite Solar Cells

A study was conducted to report a new, simple, hole transport material (HTM) composed of a central difluorinated phenyl ring, tetra-substituted with paramethoxydiarylamine groups (DFTAB). Devices fabricated using DFTAB demonstrated a stabilized PCE, had a higher energy absorption cutoff than devices utilizing the ubiquitous spiro-OMeTAD, and offered the potential to be used without the addition of ionic additives. The synthesis of DFTAB was carried out in a one pot reaction where 4,4'-dimethoxydiphenylamine was first deprotonated by NaH, followed by nucleophilic aromatic substitution of hexafluorobenzene with in situ generated amide sodium salt. The thermal properties were investigated by thermogravimetric analysis (TGA)

Dithienosilolothiophene: A New Polyfused Donor for Organic Electronics

We report the synthesis of a novel pentacyclic donor moiety, dithienosilolothiophene, and its incorporation into low bandgap semiconducting polymers. The unique geometry of this new donor allowed attaching four solubilizing side chains on the same side of the fused ring system, thus ensuring sufficient solubility when incorporated into conjugated polymers while simultaneously reducing the steric hindrance between adjacent polymer chains. The optoelectronic properties of three new polymers comprising the novel pentacyclic donor were investigated and compared to structurally similar thieno­[3,2-<i>b</i>]­thienobis­(silolothiophene) polymers. Organic solar cells were fabricated in order to evaluate the new materials’ potential as donor polymers in bulk heterojunction solar cells and gain further insight into how the single-sided side-chain arrangement affects the active layer blend morphology