Peri-Alkylated Terrylenes and Ternaphthalenes Building-Blocks Towards Multi-Edge Nanographenes

Since its first synthesis by Clar in 1948, terrylene - a fully connected ternaphthalene oligomer via naphthalene's peri-positions - has gained special focus within the rylene family, drawing interest for its unique chemical, structural, optoelectronic and single photon emission properties. In this study, we introduce a novel synthetic pathway that enhances the solubility of terrylene derivatives through complete peri-alkylation, while also facilitating extensions at the bay-positions. This approach not only broadens the scope of terrylene's chemical versatility but also opens new avenues for developing solution processable novel multi-edge nanographenes and tailoring electronic energy levels through topological edge structures. Our findings include a comprehensive structural and spectroscopic characterization along with transient absorption spectroscopy and photophysics of both the synthesized peri-alkylated terrylene and its phenylene-fused derivative.

Isolation and Structural Characterization of Regioisomers of Dibrominated Terrylene Diimides

Diverse applications of rylenediimides are attributed to the accessibility of simple methodologies to obtain versatile halogenated precursors. Terrylene diimides are important molecular platforms to achieve materials with NIR absorption and emission. In this work, we present a simple synthesis for the hitherto unknown di- and tribromo-TDIs. Regioisomerically pure dibromo TDIs, including an elusive 1,14-derivative, could be successfully isolated and structurally characterized along with tribromo-TDI. The utility of these bromo derivatives has also been demonstrated with a redox anchoring.

Temperature Tuning of Coherent Mixing between States Driving Singlet Fission in a Spiro-Fused Terrylenediimide Dimer

The excited-state dynamics of a spiro-fused terrylene-3,4:11,12-bis(dicarboximide) (TDI) dimer (sTDI2) in toluene and 2-methyltetrahydrofuran (mTHF) were investigated as a function of temperature using femtosecond- and nanosecond-transient absorption spectroscopy, as well as two-dimensional electronic spectroscopy. The spiro conjugation and the corresponding geometry of this compound guarantee a short intermonomer distance along with a partial orbital overlap between the orthogonal TDI π-electron systems, providing electronic coupling between the TDIs. Photoexcitation of sTDI2 in toluene, a low dielectric solvent, at 295 K, results in the ultrafast formation of a state composed of a coherent mixture of singlet 1(S1S0), multiexciton 1(T1T1), and charge-transfer (CT) electronic characters. This mixed species decays to decorrelated triplet states on the nanosecond timescale, completing the process of intramolecular singlet fission (SF) in sTDI2. Upon decreasing the temperature from 295 to 200 K, the contribution of the 1(T1T1) state to the mixed species decreases concurrently with an increase in the CT state character. We attribute this behavior to the variation in the vibrational energy level alignment between the states comprising the mixture due to changes in the temperature and hence the local dielectric environment. In contrast, photoexcitation of sTDI2 in more polar mTHF at 295 K results in the formation of a mixed singlet and CT state before undergoing symmetry-breaking charge separation, owing to the increased stabilization of the CT state in the medium. However, in glassy mTHF at 85 K, photoexcited sTDI2 exhibits discernible multiexciton character, comparable to that observed in toluene at 200 K, which we rationalize by the similarity of the dielectric constants under these two sets of conditions. These observations of mixed states of varying diabatic contributions over the range of experimental conditions show that the temperature and the static dielectric constant can directly control the composition of the electronically mixed excited state of sTDI2 and thus the fate of the SF process.

Giant Rylene Imide-Based Electron Acceptors for Organic Photovoltaics

ConspectusRylene imides are oligo(peri-naphthalene)s bearing one or two six-membered carboxylic imide rings. Their flexible reaction sites and unique photoelectronic properties have afforded active research for applications in photovoltaic devices, light-emitting diodes, and fluorescent sensors. Over the past few decades, synthetic flexibility along with the evolution of molecular design principles for novel aromatic imides has rendered these intriguing dyes considerably valuable, especially for organic photovoltaics (OPVs).During the course of molecular evolution, the most difficult criterion to meet is how to modulate the intra- and intermolecular interactions to alter the aggregation behavior of rylene imides as well as their compatibility with donor materials, with the prerequisite that the appropriate molecular energy level is maintained. In the meantime, our group has focused on the precise synthesis of π-extended rylene imide electron acceptors (RIAs) to rationally alter the molecular chemical and electronic structure, packing arrangement, and photoelectronic properties. These powerful molecular design strategies include the construction of a fully conjugated rigid multichromophoric architecture and successful integration of heteroatoms. Herein, these multichromophoric oligomers are precisely defined as giant rylene imides. Importantly, these strategies provide a vast space for progress in RIAs and present a more comprehensive structure-performance relationship network that can be distinguished from other electron acceptor systems. In particular, the successful acquisition of these fused superhelical architectures provides a meaningful reference for the pluralistic development of OPVs, such as triplet organic solar cells and polarized-light photovoltaic detectors. Meanwhile, the introduction of heteroatoms into the rylene conjugated skeleton provides donor/acceptor interfaces with enhanced electronic interactions and thereby suppresses the polaron-pair binding energy. Nonetheless, much remains to be implemented to broaden the absorption capability of rylene imides as well as to realize full utilization of these meaningful chiral isomers with a wide and strong UV-vis spectroscopic response.In this Account, we provide an overview of our novel approaches toward a supermolecular framework and of the reformed molecular design principle for rylene imide-based electron acceptors since 2012. We begin with a discussion of the rapidly emerging synthesis strategies for giant rylene imides. Then several typical examples with remarkable photovoltaic properties and unique working mechanisms are selected, aimed at providing an in-depth discussion of structure-property-performance relationships. The remaining challenges and newly emerging research information for giant rylene imide-based electron acceptors are further put forward. It is our aspiration that this Account will trigger intensive research interest in these pluralist rylene-based electron acceptors, thereby further accelerating the profound sustainable development of organic solar cells.

Designing a near-infrared circularly polarized luminescent dye by dissymmetric spiro-fusion

A novel spiro-fused terrylene dimer (SDT) was designed and synthesized by a dissymmetric spiro-fusion strategy. The spiro-conjugation effect caused a distinct red-shift and enhancement of the absorption spectrum. Two chiral enantiomers of SDT have been absolutely resolved and identified in combination with theoretical calculations. Circularly polarized luminescence (CPL) measurement revealed its potential as a near-infrared chiral luminescent material.

Synthesis and Supramolecular Assembly of a Terrylene Diimide Derivative Decorated With Long Branched Alkyl Chains

Terrylene diimide derivatives are pigments for dyes and optoelectric devices. A terrylene diimide derivative N,N'-di(1-undecyldodecyl)terrylene-3,4:11,12-tetracarboxdiimide (DUO-TDI) decorated with long branched alkyl chains on both imide nitrogen atoms was designed and synthesized. The supramolecular assembly behaviors of DUO-TDI in solution and at the liquid-solid interface were both investigated. The assembled nanostructures and photophysical properties of TDI in solution were explored by varying solvent polarity with spectral methods (UV-Vis, FL and FT-IR) and morphological characterization (AFM). Depending on the solution polarities, fibers, disk structures and wires could be observed and they showed diverse photophysical properties. In addition, the interfacial assembly of DUO-TDI was further investigated at the liquid-Highly Oriented Pyrolytic Graphite (HOPG) interface probed by scanning tunneling microscope (STM). Long range ordered monolayers composed of lamellar structures were obtained. The assembly mechanisms were studied for DUO-TDI both in solution and at the interface. Our investigation provides alternative strategy for designing and manipulation of supramolecular nanostructures and corresponding properties of TDI based materials.

Effect of fluorine substitution in organoboron electron acceptors for photovoltaic application

Fluorine substitution at the core unit or the endcapping groups has an interesting effect on the opto-electronic properties and device behaviors of organoboron electron acceptors.

Nonfullerene Acceptor Molecules for Bulk Heterojunction Organic Solar Cells

The bulk-heterojunction blend of an electron donor and an electron acceptor material is the key component in a solution-processed organic photovoltaic device. In the past decades, a p-type conjugated polymer and an n-type fullerene derivative have been the most commonly used electron donor and electron acceptor, respectively. While most advances of the device performance come from the design of new polymer donors, fullerene derivatives have almost been exclusively used as electron acceptors in organic photovoltaics. Recently, nonfullerene acceptor materials, particularly small molecules and oligomers, have emerged as a promising alternative to replace fullerene derivatives. Compared to fullerenes, these new acceptors are generally synthesized from diversified, low-cost routes based on building block materials with extraordinary chemical, thermal, and photostability. The facile functionalization of these molecules affords excellent tunability to their optoelectronic and electrochemical properties. Within the past five years, there have been over 100 nonfullerene acceptor molecules synthesized, and the power conversion efficiency of nonfullerene organic solar cells has increased dramatically, from ∼2% in 2012 to >13% in 2017. This review summarizes this progress, aiming to describe the molecular design strategy, to provide insight into the structure-property relationship, and to highlight the challenges the field is facing, with emphasis placed on most recent nonfullerene acceptors that demonstrated top-of-the-line photovoltaic performances. We also provide perspectives from a device point of view, wherein topics including ternary blend device, multijunction device, device stability, active layer morphology, and device physics are discussed.

Naphthalene and perylene diimides – better alternatives to fullerenes for organic electronics?

This highlight article gives an overview of the development of rylene diimide-based organic field-effect transistors and solar cells.