Perylene Diimide Dimer Research Articles

A Bis-perylene Diimide Macrocycle Chiroptical Switch.

Helical assemblies of organic dyes are ubiquitous chiral organic materials, with valuable properties including chiroptical switching due to the dynamic nature of supramolecular chirality. Herein, we report a novel chiral bis-perylene diimide macrocycle, which acts as a discrete molecular model for a chiral supramolecular assembly. Point chirality is installed through amino acid-derived imide groups which, upon macrocyclization, is translated into helical chirality in the perylene diimide dimer. In solution, the macrocycle's chiroptical properties are switchable, with both the sign (+/-) and amplitude (on/off) of the signal tuned using solvent and molecular recognition stimuli respectively. The chiral structure-property relationships identified from this macrocycle are important for the design of high fidelity supramolecular chiroptical switches.

Acceptor-acceptor′-acceptor type N-annulated perylenediimide dimeric acceptors at the outside-bay position: Synthesis and role of asymmetric 4,7-di(thien-2-yl)-5-fluorobenzothiadiazole linker

Acceptor-acceptor′-acceptor (A-A′-A) type N-annulation perylene diimide (PDI) dimeric acceptors possessed the fascinating merits but were ignored. Herein, two A-A′-A type N-annulated PDI dimers, termed as, DTBT-(PPDI-B)2 and DTFBT-(PPDI-B)2, in which the electron-deficient moieties 4,7-di(thien-2-yl)benzothiadiazole (DTBT) and monofluorinated 4,7-di(thien-2-yl)-5-fluorobenzothiadiazole (DTFBT) were selected as the central linkers and two N-annulation N-butyl-[1,12-b,c,d]pyrrole-N,Nʹ-bis(2-hexyldecyl)perylenediimide (PPDI-B) aromatic rings as the dual wings were explored. The annulation-free DTBT-(PDI-HD)2 was chosen as reference material. Owing to electron-donating of the newly formed pyrrolic aromatic ring, these studied N-annulated acceptors possessed the improved absorption and up-shifted ELUMO than those of the counterpart DTBT-(PDI-HD)2. Both of them exhibited the wide absorption spectra spanning from 300 nm to 700 nm, the similar aggregation and good photostability in solution. Monofluorinating the central benzothiadiazole linker gave the enhanced absorption, the down-shifted EHOMO and ELUMO, the reduced the dihedral angle from 9.09° to 3.64° between two N-annulated PPDI sub-planes and the enhanced solid stacking and aggregation. As a result, the N-annulation modification achieved the 0.16 V increased VOC, decreased JSC and FF, and thus the reduced PCE of 0.90 %. Moreover, the 21.33 % increased JSC of 3.64 mA cm−2 and the 35.58 % raised FF up to 42.68 % were observed in the monofluorinated PTB7-Th:DTFBT-(PPDI-B)2-based device, synergistically contributing to an 62.22 % elevated PCE of 1.46 % in spite of a 0.01 V dropped VOC. This upgradation was predominantly profited from the increased absorption, the improved exciton dissociation, elevated electron mobility and improved microstructural morphology benefiting from introducing the asymmetric 4,7-dithienyl-5-fluorobenzothiadiazole. This work demonstrates that outside bay N-annulation strategy could tune the molecular structure, energy level and thus improve the voltage, and monofluorinating the central linker is an effective tactic for regulating the molecular configuration, aggregation, morphology and thus elevating the photovoltaic performance in the A-A′-A type N-annulated PDI dimeric acceptors.

Ultrafast and Coherent Dynamics in a Solvent Switchable "Pink Box" Perylene Diimide Dimer.

Perylene diimide (PDI) dimers and higher aggregates are key components in organic molecular photonics and photovoltaic devices, supporting singlet fission and symmetry breaking charge separation. Detailed understanding of their excited states is thus important. This has proven challenging because interchromophoric coupling is a strong function of dimer architecture. Recently, a macrocyclic PDI dimer was reported in which excitonic coupling could be turned on and off simply by changing the solvent. This presents a useful case where coupling is modified without synthetic changes to tune supramolecular structure. Here we present a detailed study of solvent dependent excited state dynamics in this dimer by means of coherent multidimensional spectroscopy. Spectral analysis resolves the different coupling strengths, which are consistent with solvent dependent changes in dimer conformation. The strongly coupled conformer forms an excimer within 300 fs. The low-frequency Raman active modes recovered from two-dimensional electronic spectra reveal frequencies characteristic of exciton coupling. These are assigned to modes modulating the coupling from the corresponding DFT calculations. Further analysis reveals a time dependent frequency during excimer formation. Analysis of two-dimensional "beatmaps" reveals features in the coupled dimer which are not predicted by the displaced harmonic oscillator model and are assigned to vibronic coupling.

Distinct vibrational motions promote disparate excited-state decay pathways in cofacial perylenediimide dimers.

A complex interplay of structural, electronic, and vibrational degrees of freedom underpins the fate of molecular excited states. Organic assemblies exhibit a myriad of excited-state decay processes, such as symmetry-breaking charge separation (SB-CS), excimer (EX) formation, singlet fission, and energy transfer. Recent studies of cofacial and slip-stacked perylene-3,4:9,10-bis(dicarboximide) (PDI) multimers demonstrate that slight variations in core substituents and H- or J-type aggregation can determine whether the system follows an SB-CS pathway or an EX one. However, questions regarding the relative importance of structural properties and molecular vibrations in driving the excited-state dynamics remain. Here, we use a combination of two-dimensional electronic spectroscopy, femtosecond stimulated Raman spectroscopy, and quantum chemistry computations to compare the photophysics of two PDI dimers. The dimer with 1,7-bis(pyrrolidin-1'-yl) substituents (5PDI2) undergoes ultrafast SB-CS from a photoexcited mixed state, while the dimer with bis-1,7-(3',5'-di-t-butylphenoxy) substituents (PPDI2) rapidly forms an EX state. Examination of their quantum beating features reveals that SB-CS in 5PDI2 is driven by the collective vibronic coupling of two or more excited-state vibrations. In contrast, we observe signatures of low-frequency vibrational coherence transfer during EX formation by PPDI2, which aligns with several previous studies. We conclude that key electronic and structural differences between 5PDI2 and PPDI2 determine their markedly different photophysics.

Air processed, high open‐circuit voltage indoor organic photovoltaic cells based on side chain modified N‐annulated perylene diimides

AbstractTo achieve high‐performance indoor organic photovoltaics (OPVs), it is important to match the photoactive layer optical absorption with the light‐source emission. This can be accomplished by developing organic photoactive materials that can efficiently absorb visible light and thus minimize energy losses. While indoor OPVs have achieved efficiencies above 33% under low light intensities, the power output is limited by low open circuit voltages (VOC), often well below 1 V. In this study, we present a series of visible‐light absorbing (energy gap >1.90 eV) non‐fullerene acceptors (NFAs) based on perylene diimide dimers, which have been systematically modified with side chains of varying polarity and steric bulk (trimethyl benzyl, ethyl adamantane, trialkoxyl phenyl, and oligo ethylene glycol). Our results show that the incorporation of sterically bulky side chains such as ethyl adamantane and trimethyl benzyl, blended with the common widegap polymer PTQ10, provides photoactive layers with absorption greater than 2.0 eV, and consequently, VOCs higher than 1.2 V are achieved under AM 1.5 G illumination. Importantly, we found that the NFA with ethyl adamantane based side chains (tPDI2N‐ethyl adamantane, compound 4) exhibited the best performance, with minimized energy loss. As a result, devices using PTQ10:tPDI2N‐ethyl adamantane photoactive layers demonstrated excellent indoor efficiencies of over 16% and 18 μW cm−2 power output under a 2700 K LED lamp at 300 lux, and showed better repeatability compared to other systems. The PTQ10:tPDI2N‐ethyl adamantane based devices maintained a high VOC (>1.0 V) across a wide range of indoor lighting conditions, including 2700 K and 6500 K LED lamps. Overall, this work provides a sidechain engineering method to create NFAs for efficient indoor OPV devices.

Promotion of Fast and Efficient Singlet Fission Process of PDI Dimers by Selenium Substitution.

Singlet fission (SF) is a triplet generation mechanism capable of turning a singlet exciton into two triplet excitons. It has the potential to enhance the power conversion efficiency of single-junction solar cells. Perylene diimides (PDIs) are a class of dye molecules with photovoltaic properties and are beginning to receive more and more attention due to their potential for SF. Here, we report a selenium-substituted PDI dimer, Se-PDI-II, and we studied its SF mechanism by using steady-state, transient absorption, and time-resolved photoluminescence spectroscopy. Compared with the unsubstituted dimer PDI-II, we found that the introduction of selenium atoms can suppress excimer emission during the SF process, showing much higher SF efficiency and triplet yield.

Electronic Couplings versus Thermal Fluctuations in the Internal Conversion of Perylene Diimides: The Battle to Localize the Exciton.

Energy transfer processes among units of light-harvesting homo-oligomers impact the efficiency of these materials as components in organic optoelectronic devices such as solar cells. Perylene diimide (PDI), a prototypical dye, features exceptional light absorption and highly tunable optical and electronic properties. These properties can be modulated by varying the number of PDI units and linkers between them. Herein, atomistic nonadiabatic excited state molecular dynamics is used to explore the energy transfer during the internal conversion of acetylene and diacetylene bridged dimeric and trimeric PDIs. Our simulations reveal a significant impact of the bridge type on the transient exciton localization/delocalization between units of PDI dimers. After electronic relaxation, larger exciton delocalization occurs in the PDI dimer connected by the diacetylene bridge with respect to the one connected by the shorter acetylene bridge. These changes can be rationalized by the Frenkel exciton model. We outline a technique for deriving parameters for this model using inputs provided by nonadiabatic dynamics simulations. Frenkel exciton description reveals an interplay between the relative strengths of the diagonal and off-diagonal disorders. Moreover, atomistic simulations and the Frenkel exciton model of the PDI trimer systems corroborate in detail the localization properties of the exciton on the molecular units during the internal conversion to the lowest-energy excited state when the units become effectively decoupled. Overall, atomistic nonadiabatic simulations in combination with the Frenkel exciton model can serve as a predictive framework for analyzing and predicting desired exciton traps in PDI-based oligomers designed for organic electronics and photonic devices.

Highly photostable N-annulated perylene-diimide-based dimeric acceptors: Synthesis and role of linking core

Two N-annulated perylene diimide (PDI) dimers, termed as, TVT-(PPDI-B)2 and TYT-(PPDI-B)2, selecting (E)-1,2-di(thien-2-yl)ethylene (TVT) and 1,2-di(thien-2-yl)acetylene (TYT) as the middle linkers, N-butyl-[1,12-b,c,d]pyrrole-N,Nʹ-bis(2-hexyldecyl)perylene diimide (PPDI-B) fused aromatic moiety as two wings, were developed to investigate the influence of linking core. It was exhibited that the improved absorption, 0.05 eV up-shifted ELUMO, drastically reduced twisting angle from 68.0o to 27.9o between two N-annulated PDI moieties and enhanced molecular aggregation were found after substituting TVT linking core with TYT. Accordingly, under the best processing condition, TVT-(PPDI-B)2-based device gained the VOC of 0.92, JSC of 3.61 mA‧cm−2, FF of 30.3% and consequently PCE of 1.02% when blending with PTB7-Th. In contrast, TYT-(PPDI-B)2-based device afforded 4.35% increased VOC of 0.96 V, 86.98% enhanced JSC of 6.75 mA‧cm−2 and 55.45% raised FF of 47.1%, collectively contributed to a 211% raised PCE as high as 3.17%. This efficiency enhancement was mainly attributed to improved absorption, raised ELUMO, more efficient exciton dissociation and electron mobility, weakened charge recombination, and more suitable morphology. Interestingly, 0.12⁓0.16 V up-shifted VOC was achieved after applying N-annulation strategy at the bay-position of PDI building block. This indicates that precisely tuning the linking core in the N-annulated PDI-based dimers can effectively affect optoelectronic property, molecular geometry and morphology, and thus further boost the corresponding device efficiency.

Amorphization of fused perylene diimide dimers for high-efficiency potassium-organic batteries

A simple but efficient method to achieve stable and amorphous small-molecular carbonyls (PTCDI2) with superior rate capability and enhanced longevity of potassium-ion batteries is demonstrated.

The efficient triplet states formation of Se-modified PDI dimers and tetramers in solvents.

The triplet excited states of molecules play an important role in photophysical processes, which has attracted great research interest. Perylene diimide (PDI) is a widely studied material closely associated with the generation of triplet states, and it is highly anticipated to become an electron acceptor material for improving photovoltaic conversion efficiency. In this work, we prepared dimers and tetramers composed of selenium-modified PDI-C5 (N,N'-bis(6-undecyl) perylene-3,4,9,10-bis(dicarboximide)) units. We investigated the photophysical processes of these dimers and tetramers in chloroform and toluene using UV-visible absorption spectroscopy, fluorescence spectroscopy, and femtosecond transient absorption spectroscopy. Both the dimers and tetramers undergo efficient triplet state formation processes in the solvents. Solvents with higher polarity facilitate charge transfer thereby promote the triplet states formation. The differences in the configurations of the dimer and tetramer molecules lead to variations in triplet states generation. The twisted angles in the tetramer restricted the intramolecular electronic coupling, posing certain hindrances to exciton coupling and lowering the intramolecular CT characteristics. The emission of excimer in tetramers also competes with the triplet states formation. The research demonstrates the influence of various factors on the generation of triplet states of PDI oligomers.

Ultrafast Charge Transfer Dynamics in a Slip-Stacked Donor-Acceptor-Acceptor System.

Photoexcitation of molecular electron donor and/or acceptor chromophore aggregates can greatly affect their charge-transfer dynamics. Excitonic coupling not only alters the energy landscape in the excited state but may also open new photophysical pathways, such as symmetry-breaking charge separation (SB-CS). Here, we investigate the impact of excitonic coupling on a covalent donor-acceptor-acceptor system comprising a perylene donor (Per) and two perylenediimide (PDI) acceptor chromophores in which the three components are π-stacked in a geometry that is slipped along their long axes (Per-PDI2). Following selective photoexcitation of PDI, femtosecond transient absorption data for Per-PDI2 is compared to that for the single-donor, single-acceptor Per-PDI system, and the PDI2 dimer, which both have the same interchromophore geometry as Per-PDI2. The data show that electron transfer from Per to the lower exciton state of the PDI dimer is slower than that of the single PDI acceptor system. This is due to the lower free energy of the reaction for charge separation because of the electronic stabilization afforded by the excitonic coupling between the PDIs. While PDI2 was shown previously to undergo ultrafast SB-CS, the strong π-π electronic interaction of Per with the adjacent PDI in Per-PDI2 breaks the electronic symmetry of the PDI dimer, resulting in the oxidation of Per rather than SB-CS. These results show that the electronic coupling between molecules designed to accept charges produced by SB-CS in molecular dimers and the chromophores comprising the dimer must be balanced to favor SB-CS.

18% efficiency of ternary organic solar cells enabled by integrating a fused perylene diimide guest acceptor

Constructing ternary organic solar cells (OSCs) has been the widely used and effective strategy to further enhance photovoltaic performance. Here, a novel perylene diimide (PDI) derivative, FPDI-2PDI, was developed by attaching two PDI chromophores to the bay-position of fused PDI dimer. The wide bandgap FPDI-2PDI was used as a guest electron acceptor in the classic PM6:Y6 system. The top-performing ternary device achieved simultaneously increased open-circuit voltage (Voc) of 0.848 V, short-circuit current density (Jsc) of 27.47 mA cm-2 and fill factor (FF) of 77.20%, yielding a significantly improved power conversion efficiency (PCE) of 18.00%, which is much higher than PCE of 16.63% of the control PM6:Y6 binary device. The incorporation of FPDI-2PDI is conducive to improving solar energy utilization, suppressing charge recombination, facilitating exciton dissociation and charge collection while enhancing the blend morphology, thus leading to increased photovoltaic performance in the corresponding ternary device. This work indicates that proper molecular design will make the PDI derivatives to be very competitive guest acceptors to construct high-efficiency ternary OSCs.

An Asymmetric Perylene Diimide Dimer Acceptor for High Performance Organic Solar Cells.

The vinylene-bridged helical perylene diimide (PDI) dimer (PDI2) with a build-in twisted configuration is an alternative building block to the parent PDI for the construction of efficient non-fullerene acceptor (NFAs). Moreover, it has been proved asymmetric strategy plays a vital role in the development of NFAs. Herein, we designed and synthesized a pair of acceptor-donor-acceptor (A-D-A) type PDI2 derivatives, namely IDTIC-PDI and IDT-diPDI2, which contain asymmetric and symmetric end-cap units, respectively. To determine the structure-performance relationships of asymmetric strategy, the organic solar cells (OSCs) based on these two molecules were fabricated and measured. The asymmetric IDTIC-PDI based device exhibits a much higher PCE of 8.23 % than that of symmetric IDT-diPDI2 (5.21 %). These results reveal that symmetry breaking provides an effective way to optimize the photovoltaic performances of PDI2 based OSCs.

A graphene-like N-annulated perylene diimide dimer compound for highly efficient electrochemiluminescence

A graphene-like N-annulated perylene diimide dimer compound for highly efficient electrochemiluminescence

Conformational control of morphology for perylene diimide dimer as electron transporting material at perovskite surface

Synthesis of core-twisted perylene diimide (PDI) dimers attached with thiophene linkers (PDI-NHR-Th(1–4)) and their electron transporting ability at perovskite surface were studied. Synthesized dyes showed a high-lying lowest unoccupied molecular orbital (LUMO) energy levels between –3.68 and –3.71 eV, which were compatible with the conduction band of CH3NH3PbI2Br (–3.60 eV). Herein, we have investigated the role of the different substituted positions of PDI monomers to thiophene linkage from its (2,5)-, (3,4)-, (2,4)-, or (2,3)-positions in modulating the morphology of PDI dimer, aggregation behavior for charge transfer properties, optical shifts in ground and excited states, and recombination resistances at the interfaces of p-i-n devices. Conformational changes of PDI dimers attaching to different positions of thiophene linkers are found to affect not only photopysical dynamics of excited states of the dyes, but also charge transport kinetics at the perovskite interfaces, changing the photovoltaic performance.

Difluorobenzimidazole-decorated helical perylene diimide dimers for high-performance n-type organic field-effect transistors

N-type benzimidazole and difluorobenzimidazole fused perylene diimide dimer semiconductors were synthesized and a remarkable electronic mobility of 0.13 cm2 V−1 s−1 was obtained for a FMBI-PDI2-based organic field-effect transistor (OFET).

Progress in Functionality of Perylene Diimide Dimer Type Electron Acceptors for Perovskite Layers in Photovoltaic Applications

Progress in Functionality of Perylene Diimide Dimer Type Electron Acceptors for Perovskite Layers in Photovoltaic Applications

Conformational Control of Morphology for Perylene Diimide Dimer as Electron Transporting Material at Perovskite Surface

Conformational Control of Morphology for Perylene Diimide Dimer as Electron Transporting Material at Perovskite Surface

Keeping the chromophores crossed: evidence for null exciton splitting.

Fundamental understanding of the supramolecular assemblies of organic chromophores and the development of design strategies have seen endless ripples of interest owing to their exciting photophysical properties and optoelectronic applications. The independent discovery of dye aggregates by Jelley and Scheibe was the commencement of the remarkable advancement in the field of aggregate photophysics. Subsequent research warranted an exceptional model for defining the exciton interactions in aggregates, proposed by Davydov, Kasha and co-workers, independently, based on the long-range Coulombic coupling. Fascinatingly, the orthogonally cross-stacked molecular transition dipole arrangement was foretold by Kasha to possess null exciton interaction leading to spectroscopically uncoupled molecular assembly, which lacked an experimental signature for decades. There have been several attempts to identify and probe atypical molecular aggregates for decoding their optical behaviour. Herein, we discuss the recent efforts in experimentally verifying the unusual exciton interactions supported with quantum chemical computations, primarily focusing on the less explored null exciton splitting. Exciton engineering can be realized through synthetic modifications that can additionally offer control over the assorted non-covalent interactions for orchestrating precise supramolecular assembly, along with molecular editing. The task of attaining a minimal excitonic coupling through an orthogonally cross-stacked crystalline architecture envisaged to offer a monomer-like optical behaviour was first reported in 1,7-dibromoperylene-3,4,9,10-tetracarboxylic tetrabutylester (PTE-Br2). The attempt to stitch molecules covalently in an orthogonal fashion to possess null excitonic character culminated in a spiro-conjugated perylenediimide dimer exhibiting a monomer-like spectroscopic signature. The computational and experimental efforts to map the emergent properties of the cross-stacked architecture are also discussed here. Using the null aggregates formed by the interference effects between CT-mediated and Coulombic couplings in the molecular array is another strategy for achieving monomer-like spectroscopic properties in molecular assemblies. Moreover, identifying supramolecular assemblies with precise angle-dependent properties can have implications in functional material design, and this review can provide insights into the uncharted realm of null exciton splitting.

The impact of linker on the photovoltaic performance of helical perylene diimide based non-fullerene acceptors

Linking two or more perylene diimide (PDI) directly together and/or with congested spacers at the N-position, α- or bay-region is a robust strategy for constructing high-performance non-fullerene acceptors (NFAs). On the other hand, ethylene fused PDI dimer (PDI2) has emerged as alternative building blocks to the parent PDI in constructing NFAs owing to the built-in twisted configuration, outstanding optoelectronic properties, concise gram-scale synthesis and so forth in recent years. In line with the parent PDI, tailoring PDI2 by dimerization, trimerization as well as by introduction of heteroatoms can also result in enhanced photovoltaic performance. However, to the best of our knowledge, most of the modifications occurred at the bay region of PDI2. In this contribution, two PDI2 dimers namely P2–P2, P2–C6–P2 are constructed by using hydrazine and 1,6-hexanediamine as linkers at imide positions. The photovoltaic performance of these two NFAs as well as the parent PDI2 were evaluated using commercially available PM6 as the electron donor. The two PDI2 dimers show superior photovoltaic performances compared with PDI2 and P2–C6–P2 gives the best power conversion efficiency (PCE) of 8.03% among these three NFAs. These results argue that modification at the imide groups is also a robust strategy for constructing high-performance PDI2-based NFAs and the choice of linkers plays a vital role in device performance.