Inducing Single-Handed Helicity in a Twisted Molecular Nanoribbon.

Molecular conformation has an important role in chemistry and materials science. Molecular nanoribbons can adopt chiral twisted helical conformations. However, the synthesis of single-handed helically twisted molecular nanoribbons still represents a considerable challenge. Herein, we describe an asymmetric approach to induce single-handed helicity with an excellent degree of conformational discrimination. The chiral induction is the result of the chiral strain generated by fusing two oversized chiral rings and of the propagation of that strain along the nanoribbon's backbone.

Redox-Switchable Complexes Based on Nanographene-NHCs.

A series of rhodium and iridium complexes with a N-heterocyclic carbene (NHC) ligand decorated with a perylene-diimide-pyrene moiety are described. Electrochemical studies reveal that the complexes can undergo two successive one-electron reduction events, associated to the reduction of the PDI moiety attached to the NHC ligand. The reduction of the ligand produces a significant increase on its electron-donating character, as observed from the infrared spectroelectrochemical studies. The rhodium complex was tested in the [3+2] cycloaddition of diphenylcyclopropenone and methylphenylacetylene, where it displayed a redox-switchable behavior. The neutral complex showed moderate activity, which was suppressed when the catalyst was reduced.

Twisted Molecular Nanoribbons with up to 53 Linearly-Fused Rings.

The synthesis of three molecular nanoribbons with a twisted aromatic framework is described. The largest one shows a 53 linearly fused rings backbone (12.9 nm) and 322 conjugated atoms in its aromatic core (C296N24S2). This new family of nanoribbons shows extremely high molar absorptivities, reaching 986 100 M-1 cm-1, and red-emitting properties.

Perylene Bisimide Dyes with up to Five Independently Introduced Substituents: Controlling the Functionalization Pattern and Photophysical Properties Using Regiospecific Bay Substitution.

We report herein a versatile and user-friendly synthetic methodology based on sequential functionalization that enables the synthesis of previously unknown perylene bisimide (PBI) dyes with up to five different substituents attached to the perylene core (e.g., compound 15). The key to the success of our strategy is a highly efficient regiospecific 7-mono- and 7,12-di-phenoxy bay substitution at the "imide-activated" 7- and 12-bay positions of 1,6,7,12-tetrachloroperylene monoimide diester 1. The facile subsequent conversion of the diester groups into an imide group resulted in novel PBIs (e.g., compound 14) with two phenoxy substituents specifically at the 7- and 12-bay positions. This conversion led to the activation of C-1 and C-6 bay positions, and thereafter, the remaining two chlorine atoms were substituted to obtain tetraphenoxy-PBI (compound 15) that has two different imide and three different bay substituents. The methodology provides excellent control over the functionalization pattern, which enables the synthesis of various regioisomeric pairs bearing the same bay substituents. Another important feature of this strategy is the high sensitivity of HOMO-LUMO energies and photoinduced charge transfer toward sequential functionalization. As a result, systematic fluorescence on-off switching has been demonstrated upon subsequent substitution with the electron-donating 4-methoxyphenoxy substituent.

Relation between molecular packing and singlet fission in thin films of brominated perylenediimides.

Perylene diimides (PDIs) are attractive chromophores that exhibit singlet exciton fission (SF) and have several advantages over traditional SF molecules such as tetracene and pentacene; however, their photophysical properties relating to SF have received only limited attention. In this study, we explore how introduction of bulky bromine atoms in the so-called bay-area PDIs, resulting in a nonplanar structure, affects the solid-state packing and efficiency of singlet fission. We found that changes in the molecular packing have a strong effect on the temperature dependent photoluminescence, expressed as an activation energy. These effects are explained in terms of excimer formation for PDIs without bay-area substitution, which competes with singlet fission. Introduction of bromine atoms in the bay-positions strongly disrupts the solid-state packing leading to strongly reduced excitonic interactions. Surprisingly, these relatively amorphous materials with weak electronic coupling exhibit stronger formation of triplet excited states by SF because the competing excimer formation is suppressed here.

A Molecular Level Approach To Elucidate the Supramolecular Packing of Light-Harvesting Antenna Systems.

The molecular geometry and supramolecular packing of two bichromophoric prototypic light harvesting compounds D1A2 and D2A2, consisting of two naphthylimide energy donors that were attached to the 1,7 bay positions of a perylene monoimide diester energy acceptor, have been determined by a hybrid approach using magic angle spinning NMR spectroscopy and electron nano-crystallography (ENC), followed by modelling. NMR shift constraints, combined with the P 1 ‾ space group obtained from ENC, were used to generate a centrosymmetric dimer of truncated perylene fragments. This racemic packing motif is used in a biased molecular replacement approach to generate a partial 3D electrostatic scattering potential map. Resolving the structure of the bay substituents is guided by the inversion symmetry, and the distance constraints obtained from heteronuclear correlation spectra. The antenna molecules form a pseudocrystalline lattice of antiparallel centrosymmetric dimers with pockets of partially disordered bay substituents. The two molecules in a unit cell form a butterfly-type arrangement. The hybrid methodology that has been developed is robust and widely applicable for critical structural underpinning of self-assembling structures of large organic molecules.

Substitution Effects on the Photoinduced Charge-Transfer Properties of Novel Perylene-3,4,9,10-tetracarboxylic Acid Derivatives.

We report here the synthesis and photophysical study of a series of electron donor-acceptor molecules, in which electron-donating 4-methoxyphenoxy groups are attached to the 1,7-bay positions of four different perylene tetracarboxylic acid derivatives, namely, perylene tetraesters 1, perylene monoimide diesters 2, perylene bisimides 3, and perylene monobenzimidazole monoimides 4. These perylene derivatives are used because of their increasing order of electron-accepting capability upon moving from 1 to 4. Two additional donor-acceptor molecules are synthesized by linking electron-donating 4-methoxyphenyl groups to the imide position of perylene monoimide diester 2 and perylene bisimide 3. The motivation for this study is to achieve a good control over the photoinduced charge-transfer (CT) process in perylene-based systems by altering the position of electron donors and tuning the electron deficiency of perylene core. A comprehensive study of the photophysical properties of these molecules has shown a highly systematic trend in the magnitude of CT as a function of increased electron deficiency of the perylene core and solvent polarity. Importantly, just by changing the attachment of electron-donating group from "bay" to "imide" position, we are able to block the CT process. This implies that the positioning of the electron donor at the perylene core strongly influences the kinetics of the photoinduced CT process. In these compounds, the CT process is characterized by the quenching of fluorescence and singlet excited-state lifetimes as compared to model compounds bearing non-electron-donating 4-tert-butylphenoxy groups. Transient absorption spectroscopy did not reveal spectra of CT states. This most likely implies that the CT state is not accumulated, because of the faster charge recombination.

Fluorescent PET probes based on perylene-3,4,9,10-tetracarboxylic tetraesters.

Perylene-3,4,9,10-tetracarboxylic tetraester-based fluorescent PET probes with aniline receptors attached either at the peri- or the bay-positions have been synthesized. By attaching aniline receptors at the bay position, pH-sensitive "light-up" probes, with fluorescence quantum yields ΦF > 0.75 and fluorescent enhancements FE > 500 in ethanol, have been obtained.

Synthesis of regioisomerically pure 1,7-dibromoperylene-3,4,9,10-tetracarboxylic acid derivatives.

The perylene derivative 1,7-dibromoperylene-3,4,9,10-tetracarboxylic tetrabutylester has been obtained in regioisomerically pure form, by employing a highly efficient, scalable, and robust synthesis starting from commercially available perylene-3,4,9,10-tetracarboxylic bisanhydride. Subsequently, this compound is utilized for the synthesis of extremely valuable and versatile regioisomerically pure intermediates, namely, 1,7-dibromoperylene-3,4,9,10-tetracarboxylic dibutylester monoanhydride, 1,7-dibromoperylene-3,4,9,10-tetracarboxylic bisanhydride, and 1,7-dibromoperylene monoimid monoanhydride. These compounds possess at least one anhydride functionality in addition to the 1,7 bromo substituents and thus allow for a virtually limitless attachment of substituents both at the "peri" and the "bay" positions. The intermediate 1,7-dibromoperylene monoimide monoanhydride is of special interest as it provides access to unsymmetrically imide-substituted 1,7-dibromoperylene derivatives, which are not accessible by previously known procedures. Finally, substitution of the 1,7 bromine atoms in the bay area by phenoxy groups, which is a generally applied reaction for 1,7-dibromoperylene bisimides, was proven to be equally effective for a 1,7-dibromoperylene tetraester and a 1,7-dibromoperylene diester monoimid.

Sequential Synthesis and Secondary Structure Analysis of Two Classes of Perylene Bisimide Oligomers.

An iterative step-by-step synthetic approach is employed to form perylene bisimide (PBI) oligomers of defined sizes by connecting the PBI units through their imide positions via a benzyl linker. The versatility of this approach was showcased by its successful implementation on two different PBI building blocks to achieve two separate series of oligomers (up to the pentamer) with modulated conformations: one with an open random coil oligomer and one with an H-type foldamer architecture.

Direct evidence of significantly different chemical behavior and excited-state dynamics of 1,7- and 1,6-regioisomers of pyrrolidinyl-substituted perylene diimide.

Novel bay-functionalized perylene diimides with additional substitution sites close to the perylene core have been prepared by the reaction between 1,7(6)-dibromoperylene diimide 6 (dibromo-PDI) and 2-(benzyloxymethyl)pyrrolidine 5. Distinct differences in the chemical behaviors of the 1,7- and 1,6-regioisomers have been discerned. While the 1,6-dibromo-PDI produced the corresponding 1,6-bis-substituted derivative more efficiently, the 1,7-dibromo-PDI underwent predominant mono-debromination, yielding a mono-substituted PDI along with a small amount of the corresponding 1,7-bis-substituted compound. By varying the reaction conditions, a controlled stepwise bis-substitution of the bromo substituents was also achieved, allowing the direct synthesis of asymmetrical 1,6- and 1,7-PDIs. The compounds were isolated as individual regioisomers. Fullerene (C60) was then covalently linked at the bay region of the newly prepared PDIs. In this way, two separate sets of perylene diimide-fullerene dyads, namely single-bridged (SB-1,7-PDI-C60 and SB-1,6-PDI-C60) and double-bridged (DB-1,7-PDI-C60 and DB-1,6-PDI-C60), were synthesized. The fullerene was intentionally attached at the bay region of the PDI to achieve close proximity of the two chromophores and to ensure an efficient photoinduced electron transfer. A detailed study of the photodynamics has revealed that photoinduced electron transfer from the perylene diimide chromophore to the fullerene occurs in all four dyads in polar benzonitrile, and also occurs in the single-bridged dyads in nonpolar toluene. The process was found to be substantially faster and more efficient in the dyads containing the 1,7-regioisomer, both for the singly- and double-bridged molecules. In the case of the single-bridged dyads, SB-1,7-PDI-C60 and SB-1,6-PDI-C60, different relaxation pathways of their charge-separated states have been discovered. To the best of our knowledge, this is the first observation of photoinduced electron transfer in PDI-C60 dyads in a nonpolar medium.

Excited-state interaction of red and green perylene diimides with luminescent Ru(II) polypyridine complex.

Three new perylene diimide (PDI)-based ligands have been synthesized by the covalent attachment of dipyrido[a,c]phenazine moiety to one of the bay-positions of PDI, while the second position has been substituted with either a 4-tert-butylphenoxy or a pyrrolidinyl group to obtain two types of chromophores, Ph-PDI and Py-PDI, respectively, with distinct properties. In the case of Py-PDI, the resultant 1,7- and 1,6-regioisomers have been successfully separated by column chromatography and characterized by (1)H NMR spectroscopy. The ligands have been employed to prepare donor-acceptor-based ensembles incorporating the covalently linked PDI and Ru(II) polypyridine complex as the acting chromophores. A comprehensive study of the excited-state photodynamics of the ensembles has been performed by means of electrochemical and steady state and time-resolved spectroscopic methods. Although, in all the three ensembles, the photoexcitation of either chromophore resulted in a long-lived triplet excited state of PDI ((3)PDI) as the final excited state, the photochemical reactions leading to the triplet states were found to be essentially different for the two types of the ensembles. In the case of the Ph-PDI-based ensemble, the excitation of either chromophore leads to the electron transfer from the Ru(II) complex to Ph-PDI, whereas for the Py-PDI-based ensembles, the electron transfer is observed in the opposite direction and only when the Ru(II) complex is excited. The difference in the behavior was rationalized based on electrochemical study of the compounds, which has shown that the Ph-PDI chromophore is a better electron acceptor and the Py-PDI chromophores are relatively better electron donors. This study shows a chemical approach to control the photoreactions in PDI-based dichromophoric ensembles including the possibility to switch the direction of the photoinduced electron transfer.

Tuning the Driving Force for Charge Transfer in Perovskite-Chromophore Systems.

Understanding the interplay between the kinetics and energetics of photophysical processes in perovskite-chromophore hybrid systems is crucial for realizing their potential in optoelectronics, photocatalysis, and light-harvesting applications. By combining steady-state optical characterizations and transient absorption spectroscopy, we have investigated the mechanism of interfacial charge transfer (CT) between colloidal CsPbBr3 nanoplatelets (NPLs) and surface-anchored perylene derivatives and have explored the possibility of controlling the CT rate by tuning the driving force. The CT driving force was tuned systematically by attaching acceptors with different electron affinities and by varying the bandgap of NPLs via thickness-controlled quantum confinement. Our data show that the charge-separated state is formed by selectively exciting either the electron donors or acceptors in the same system. Upon exciting attached acceptors, hole transfer from perylene derivatives to CsPbBr3 NPLs takes place on a picosecond time scale, showing an energetic behavior in line with the Marcus normal regime. Interestingly, such energetic behavior is absent upon exciting the electron donor, suggesting that the dominant CT mechanism is energy transfer followed by ultrafast hole transfer. Our findings not only elucidate the photophysics of perovskite-molecule systems but also provide guidelines for tailoring such hybrid systems for specific applications.

Molecular nanoribbon gels.

Herein, we show that twisted molecular nanoribbons with as many as 322 atoms in the aromatic core are efficient gelators capable of self-assembling into ordered π-gels with morphologies and sol-gel transitions that vary with the length of the nanoribbon. In addition, the nanoribbon gels show a red fluorescence and also pseudoconductivity values in the same range as current state-of-the-art π-gels.

Yellow Light-Emitting Highly Soluble Perylene Bisimide Dyes by Acetalization of Bay-Hydroxy Groups.

A new class of perylene bisimide (PBI) derivatives is introduced by bridging 1,12- and 1,6,7,12-hydroxy functionalized bay positions with oxygen-carbon-oxygen linker(s). This functionalization rigidifies the inherently twisted bay-substituted perylene core to afford dyes of high stability and solubility that are characterized by vibronically well-resolved absorption and fluorescence spectra and intense yellow emission with quantum yields close to 100%.

Efficacious elimination of intramolecular charge transfer in perylene imide based light-harvesting antenna molecules.

Two light-harvesting antenna molecules were obtained by positioning naphthalene monoimide energy donors at the imide position, instead of the bay positions, of perylene imide energy acceptors. Such rational design resulted in a complete suppression of parasitic intramolecular charge transfer without compromising the desired ultrafast rates of excitation energy transfer.

Overcoming the exciton binding energy in two-dimensional perovskite nanoplatelets by attachment of conjugated organic chromophores.

In this work we demonstrate a novel approach to achieve efficient charge separation in dimensionally and dielectrically confined two-dimensional perovskite materials. Two-dimensional perovskites generally exhibit large exciton binding energies that limit their application in optoelectronic devices that require charge separation such as solar cells, photo-detectors and in photo-catalysis. Here, we show that by incorporating a strongly electron accepting moiety, perylene diimide organic chromophores, on the surface of the two-dimensional perovskite nanoplatelets it is possible to achieve efficient formation of mobile free charge carriers. These free charge carriers are generated with ten times higher yield and lifetimes of tens of microseconds, which is two orders of magnitude longer than without the peryline diimide acceptor. This opens a novel synergistic approach, where the inorganic perovskite layers are combined with functional organic chromophores in the same material to tune the properties for specific applications.

Scalable Route to Electroactive and Light Active Perylene Diimide Dye Polymer Binder for Lithium-Ion Batteries.

Developing multifunctional polymeric binders is key to the design of energy storage technologies with value-added features. We report that a multigram-scale synthesis of perylene diimide polymer (PPDI), from a single batch via polymer analogous reaction route, yields high molecular weight polymers with suitable thermal stability and minimized solubility in electrolytes, potentially leading to improved binding affinity toward electrode particles. Further, it develops strategies for designing copolymers with virtually any desired composition via a subsequent grafting, leading to purpose-built binders. PPDI dye as both binder and electroactive additive in lithium half-cells using lithium iron phosphate exhibits good electrochemical performance.

Tailoring Photophysical Processes of Perylene-Based Light Harvesting Antenna Systems with Molecular Structure and Solvent Polarity.

The excited-state dynamics of perylene-based bichromophoric light harvesting antenna systems has been tailored by systematic modification of the molecular structure and by using solvents of increasing polarity in the series toluene, chloroform, and benzonitrile. The antenna systems consist of blue light absorbing naphthalene monoimide (NMI) energy donors (D1, D2, and D3) and the perylene derived green light absorbing energy acceptor moieties, 1,7-perylene-3,4,9,10-tetracarboxylic tetrabutylester (A1), 1,7-perylene-3,4,9,10-tetracarboxylic monoimide dibutylester (A2), and 1,7-perylene-3,4,9,10-tetracarboxylic bisimide (A3). The design of these antenna systems is such that all exhibit ultrafast excitation energy transfer (EET) from the excited donor to the acceptor, due to the effective matching of optical properties of the constituent chromophores. At the same time, electron transfer from the donor to the excited acceptor unit has been limited by the use of a rigid and nonconjugated phenoxy bridge to link the donor and acceptor components. The antenna molecules D1A1, D1A2, and D1A3, which bear the least electron-rich energy donor, isopentylthio-substituted NMI D1, exhibited ultrafast EET (τEET ∼ 1 ps) but no charge transfer and, resultantly, emitted a strong yellow-orange acceptor fluorescence upon excitation of the donor. The other antenna molecules D2A2, D2A3, and D3A3, which bear electron-rich energy donors, the amino-substituted NMIs D2 and D3, exhibited ultrafast energy transfer that was followed by a slower (ca. 20-2000 ps) electron transfer from the donor to the excited acceptor. This charge transfer quenched the acceptor fluorescence to an extent determined by molecular structure and solvent polarity. These antenna systems mimic the primary events occurring in the natural photosynthesis, i.e., energy capture, efficient energy funneling toward the central chromophore, and finally charge separation, and are suitable building blocks for achieving artificial photosynthesis, because of their robustness and favorable and tunable photophysical properties.