Perylene Bisimide Dimer Research Articles

Bisperylene bisimide based conjugated polymer as electron acceptor for polymer-polymer solar cells

Perylene bisimide (PBI) unit has been widely used to design conjugated materials, which can be used as electron acceptor in organic solar cells due to its strong electron-deficient ability. In this work, a conjugated polymer based on PBI dimer as monomer was designed, synthesized, and compared to the conjugated polymer containing single PBI as repeating units. The two conjugated polymers were found to have similar molecular weight, absorption spectra and energy levels. Density functional theory calculation revealed that the PBI dimer-based polymer exhibited highly twisted conjugated backbone due to the large dihedral angle between the two PBI units. The PBI-based polymers as electron acceptor were applied into polymer-polymer solar cells, in which PBI dimer-based polymer solar cells were found to show a high short circuit current density (J sc = 11.2 mA∙cm−2 and a high power conversion efficiency (PCE) of 4.5%. In comparison, the solar cells based on PBI-based polymer acceptor only provided a J sc of 7.2 mA∙cm−2 and PCE of 2.5%. The significantly enhanced PCE in PBI dimer-based solar cells was attributed to the mixed phase in blended thin films, as revealed by atom force microscopy. This study demonstrates that PBI dimer can be used to design polymer acceptors for high performance polymerpolymer solar cells.

On the applicability of time‐dependent density functional theory (TDDFT) and semiempirical methods to the computation of excited‐state potential energy surfaces of perylene‐based dye‐aggregates

AbstractThe excited states of perylene‐based dye aggregates were investigated with emphasis on the description of the potential energy surfaces for the intermolecular motion in a dimer, which are of importance for exciton trapping. The aim is to investigate the applicability of TDDFT and semiempirical methods. The longitudinal displacement of two π‐stacked molecules against each other is used as model and the methods are benchmarked against SCS‐CC2 and SCS‐ADC(2). Furthermore a simple character analysis is applied. In the case of the perylene dimer, CAM‐B3LYP and ωB97XD provide accurate results. However, while CAM‐B3LYP fails for the PBI (perylene bisimide) dimer the performance of ωB97XD is highly dependent on the used monomer geometry due to close‐lying diabatic states. A change in geometry changes the character of the excited states even qualitatively. The accuracy of several other long‐range corrected functionals (LC‐BLYP, LC‐ωPBE, ωB97X) and the effect of empirically tuning the range‐separation parameter of ωB97XD are also presented for this interesting case. Furthermore, it is shown that the semiempirical method OM2 fails to provide a correct description of the excited states when the orbital overlap plays a significant role. This is attributed to the too contracted basis set.

Sensing of Double-Stranded DNA/RNA Secondary Structures by Water Soluble Homochiral Perylene Bisimide Dyes.

A broad series of homochiral perylene bisimide (PBI) dyes were synthesized that are appended with amino acids and cationic side chains at the imide positions. Self-assembly behavior of these ionic PBIs has been studied in aqueous media by UV/Vis spectroscopy, revealing formation of excitonically coupled H-type aggregates. The interactions of these ionic PBIs with different ds-DNA and ds-RNA have been explored by thermal denaturation, fluorimetric titration and circular dichroism (CD) experiments. These PBIs strongly stabilized ds-DNA/RNA against thermal denaturation as revealed by high melting temperatures of the formed PBI/polynucleotide complexes. Fluorimetric titrations showed that these PBIs bind to ds-DNA/RNA with high binding constants depending on the number of the positive charges in the side chains. Thus, spermine-containing PBIs with six positive charges each showed higher binding constants (logKs =9.2-9.8) than their dioxa analogues (logKs =6.5-7.9) having two positive charges each. Induced circular dichroism (ICD) of PBI assemblies created within DNA/RNA grooves was observed. These ICD profiles are strongly dependent on the steric demand of the chiral substituents of the amino acid units and the secondary structure of the DNA or RNA. The observed ICD effects can be explained by non-covalent binding of excitonically coupled PBI dimer aggregates into the minor groove of DNA and major groove of RNA which is further supported by molecular modeling studies.

Suppressed charge recombination in polymer solar cells based on perylene diimide derivative acceptors via solvent vapor annealing

A singly-linked perylene bisimide dimer (di-PBI) and a low band gap polymer based on dithienocarbazole and isoindigo moieties (P(IID-DTC)) are selected as electron acceptor and donor respectively to fabricate non-fullerene based polymer solar cells. The combination of di-PBI acceptor and P(IID-DTC) donor provides well overlapped absorption profile with solar light in the visible region. The P(IID-DTC):di-PBI blend morphology and its effect on charge transport and recombination have been investigated in detail. The dominant bimolecular recombination in commonly processed P(IID-DTC):di-PBI blend results in a low power conversion efficiency of merely 1%. We find that CH2Cl2 vapor annealing can effectively improve bi-continuous phase separation and boost the electron transport by more than two orders of magnitude due to the detrap of di-PBI molecules from amorphous P(IID-DTC) matrix. More importantly, the dominant bimolecular recombination in the P(IID-DTC):di-PBI blend films is strongly suppressed. Finally, the power conversion efficiency of non-fullerene P(IID-DTC):di-PBI blend solar cell is dramatically improved to 2.95%.

Phenylene ethynylene-tethered perylene bisimide folda-dimer and folda-trimer: investigations on folding features in ground and excited states.

In this work, we have elucidated in detail the folding properties of two perylene bisimide (PBI) foldamers composed of two and three PBI units, respectively, attached to a phenylene ethynylene backbone. The folding behaviors of these new PBI folda-dimer and trimer have been studied by solvent-dependent UV/Vis absorption and 1D and 2D NMR spectroscopy, revealing facile folding of both systems in tetrahydrofuran (THF). In CHCl3 the dimer exists in extended (unfolded) conformation, whereas partially folded conformations are observed in the trimer. Temperature-dependent (1) H NMR spectroscopic studies in [D8 ]THF revealed intramolecular dynamic processes for both PBI foldamers due to, on the one hand, hindered rotation around CN imide bonds and, on the other hand, backbone flapping; the latter process being energetically more demanding as it was observed only at elevated temperature. The structural features of folded conformations of the dimer and trimer have been elucidated by different 2D-NMR spectroscopy (e.g., ROESY and DOSY) in [D8 ]THF. The energetics of folding processes for the PBI dimer and trimer have been assessed by calculations applying various methods, particularly the semiempirical PM6-DH2 and the more sophisticated B97D approach, in which relevant dispersion corrections are included. These calculations corroborate the results of NMR spectroscopic studies. Folding features in the excited states of these PBI foldamers have been characterized by using time-resolved fluorescence and transient absorption spectroscopy in THF and CHCl3 , exhibiting similar solvent-dependent behavior as observed for the ground state. Interestingly, photoinduced electron transfer (PET) process from electron-donating backbone to electron-deficient PBI core for extended, but not for folded, conformations was observed, which can be explained by a fast relaxation of excited PBI stacks in the folded conformation into fluorescent excimer states.

Spectroscopic Demonstration of Exciton Dynamics and Excimer Formation in a Sterically Controlled Perylene Bisimide Dimer Aggregate.

Although it is commonly known that H-type PBI aggregates give rise to a broad, red-shifted excimer fluorescence with considerably longer fluorescence lifetimes than observed for the monomers, the underlying mechanisms of excimer formation and other relevant exciton dynamics in such π-stacked systems are still far from being understood. In this context, we demonstrate a thorough spectroscopic investigation on the exciton relaxation pathways, including excimer formation, in a perylene-3,4:9,10-bis(dicarboximide) (PBI) dimer aggregate 1 by using time-resolved fluorescence and transient absorption spectroscopy combined with excitation-power and polarization dependence. It was found that the excited dimer formation process followed by structural rearrangement is approximately two times faster than observed within larger PBI aggregates. Excitation-power-dependent transient absorption decay profiles revealed the fully delocalized nature of excitons in the dimer as opposed to larger stacks.

A new efficient method for calculation of Frenkel exciton parameters in molecular aggregates.

The Frenkel exciton Hamiltonian is at the heart of many simulations of excitation energy transfer in molecular aggregates. It separates the aggregate into Coulomb-coupled monomers. Here it is shown that the respective parameters, i.e., monomeric excitation energies and Coulomb couplings between transition densities can be efficiently calculated using time-dependent tight-binding-based density functional theory (TD-DFTB). Specifically, Coulomb couplings are expressed in terms of self-consistently determined Mulliken transition charges. The approach is applied to two dimer systems. First, formaldehyde oxime for which a detailed comparison with standard DFT using the B3LYP and the PBE functionals as well as with SCS-CC2 is provided. Second, the Coulomb coupling is explored in dependence on the intermolecular coordinates for a perylene bisimide dimer. This provides structural evidence for the previously observed biphasic aggregation behavior of this dye.

Theoretical Analysis of the Relaxation Dynamics in Perylene Bisimide Dimers Excited by Femtosecond Laser Pulses

We present a model for the relaxation dynamics in perylene bisimide dimers, which is based on ab initio electronic structure and quantum dynamics calculations including effects of dissipation. The excited-state dynamics proceeds via a mixing of electronic states of local Frenkel and charge-transfer characters, which becomes effective upon a small distortion of the dimer geometry. In this way, it is possible to explain the fast depopulation of the photoexcited state, which we characterize by femtosecond transient absorption measurements. The combined theoretical and experimental analysis hints at a trapping mechanism, which involves nonadiabatic and dissipative dynamics in an excited-state vibronic manifold and provides an atomistic picture that might prove valuable for future design of photovoltaic materials.

Cover Picture: Perylene Bisimide Dimer Aggregates: Fundamental Insights into Self‐Assembly by NMR and UV/Vis Spectroscopy (Chem. Eur. J. 43/2012)

Widely applied automotive color pigments based on perylene bisimide have been utilized by many groups to create extended one-dimensional π stacks by self-assembly. In their Full Paper on page 13665 ff., F. Würthner et al. report on the application of sterically demanding groups to terminate self-assembly at the dimer stage. Only in highly nonpolar aliphatic solvents, a rather unusual growth into larger self-assembled structures is observed.

Perylene Bisimide Dimer Aggregates: Fundamental Insights into Self‐Assembly by NMR and UV/Vis Spectroscopy

A novel perylene bisimide (PBI) dye bearing one solubilizing dialkoxybenzyl and one bulky 2,5-di-tert-butylphenyl substituent was synthesized and its aggregation behavior was analyzed by NMR and UV/Vis spectroscopy in various chloroform/methylcyclohexane (MCH) solvent mixtures. In the presence of no less than 10 vol % chloroform, exclusive self-assembly of this PBI dye into π-stacked dimers was unambiguously confirmed by means of both concentration-dependent (1) H NMR and UV/Vis spectroscopic experiments. Based on ROESY NMR, a well-defined π-stacked dimer structure was determined and further corroborated by molecular modeling studies. By varying the solvent composition of chloroform and MCH, the solvent effects on the Gibbs free energy of PBI dimerization were elucidated and showed a pronounced nonlinearity between lower and higher MCH contents. This observation could be related to a further growth process of dimers into larger aggregates that occurs in the absence of chloroform, which is required to solvate the aromatic π surfaces. With the help of a single-crystal structure analysis for a related PBI dye, a structural model could be derived for the extended aggregates that are still composed of defined π-π-stacked PBI dimer entities.

TPD doped polystyrene as charge transporter in DiPBI sensitized photorefractive composites

We incorporate a mixture of polystyrene (PS) and the highly conductive N, N′-diphenyl-N, N′-bis(3-methylphenyl)-[1, 1′-biphenyl]-4, 4′-diamine (TPD) as charge transporting agent into a photorefractive composite, wherein the liquid crystal 4-cyano-4-n-pentylbiphenyl (5CB) is the electro-optical unit and the perylene bisimide dimer DiPBI acts as sensitizing component. Investigation of the photocurrent reveals a strong enhancement of the photoconductivity. Compared to composites, wherein poly-n-vinylcarbazole (PVK) is the charge transporting agent, the internal photocurrent efficiency is enhanced 11 times. This dramatic improvement is attributed to an increase of charge generation and transport and it allows for a reduction of the applied electric field to get a photoconductivity that is comparable to PVK comprising composites.

Ensemble and Single-Molecule Spectroscopic Study on Excitation Energy Transfer Processes in 1,3-Phenylene-Linked Perylenebisimide Oligomers

1,3-Phenylene-bridged perylenebisimide dimer (PBI2) and trimer (PBI3) were prepared along with monomer reference (PBI1) using perylene imide-anhydride 5 as a key precursor. 3,3-Dimethylbut-1-yl substituents were introduced at the 2,5-positions of perylenebisimide (PBI) to improve the solubilities of PBI oligomers. Actually, no serious aggregation of PBI2 and PBI3 was detected in their dilute CH(2)Cl(2) solutions. Under these conditions, intramolecular electronic interactions among PBI chromophores have been revealed by measuring the photophysical properties at their ensemble and single-molecule levels. The excitation energy transfer times of PBI2 (0.16 ps) and PBI3 (0.60 ps) were determined from the two different observables, anisotropy depolarization, and singlet-singlet annihilation, respectively, which are considered as the incoherent Förster-type energy hopping (EEH) times as compared with the EEH time constant (1.97 ps) calculated on the basis of the Förster mechanism. The relatively short EEH times compared to similar PBI oligomers can be attributed to 1,3-phenylene linker, which assures a short distance between the chromophores and, as a consequence, makes it hard to treat the PBI unit as a point dipole. The limitation of point-dipole approximation to describe the PBI oligomers and additional through-bond type interactions can be attributed as the causes of the discrepancies in excitation energy transfer times. Considering these photophysical properties, we can suggest that 1,3-phenylene-linked PBI oligomers have potentials as molecular photonic devices including the artificial light-harvesting system.

Single molecule studies of calix[4]arene-linked perylene bisimide dimers: relationship between blinking, lifetime and/or spectral fluctuations

We recorded fluorescence time traces, and simultaneously either the fluorescence lifetime or the emission spectra from single perylene bisimide (PBI) dimers embedded in a polystyrene matrix. In these traces three distinct intensity levels can be distinguished, which reflect the photo-induced radicalisation of one of the perylene subunits. Differences in the energy transfer rate between the neutral PBI and the reversibly formed radical anion give rise to variations in the chronological order of the appearance of the intensity levels, which allowed us to categorise the time traces into three distinct groups: Type 1 blinking corresponds to a high energy transfer rate, type 2 blinking to fluctuations between large and small transfer rates (dynamic quenching), and type 3 blinking results from small energy transfer rates together with Coulomb blockade. The information that we obtain from the distributions of the fluorescence lifetimes at the various signal levels allows us to relate these differences to properties of the local polymer environment of the dimers.

Interaction of spermine-alanine functionalized perylene bisimide dye aggregates with ds-DNA/RNA secondary structure

We report for the first time on the interaction of self-assembled perylene bisimide (PBI) dye aggregates with polynucleotides, revealing very high (nM) binding constants and exceptional thermal stabilization of double-stranded (ds)-DNA/RNA. Induced CD profiles of PBI dimer aggregates formed within DNA/RNA grooves show high sensitivity on the steric properties of the binding site, suggesting the applicability of such self-adjusting excitonically coupled PBI dimers for the sensing of the DNA/RNA secondary structure.

Nature of Low-Lying Excited States in H-Aggregated Perylene Bisimide Dyes: Results of TD-LRC-DFT and the Mixed Exciton Model

We characterize the nature of the low-lying excited states in H-aggregated perylene bisimide (PBI) dyes in terms of the recently proposed long-range-corrected density functional theory (LRC-DFT) and the mixed intramolecular Frenkel exciton (FE) and the intermolecular charge-transfer exciton (CTE) model. The singlet vertical excitation energies of H-aggregated PBI dimers and multimers are theoretically evaluated by considering the aggregation details. It is found that the dimer absorption follows closely the spectra of PBI aggregates in solution and demonstrates strong mixing of two kinds of excitons. The experimentally observed low-energy absorption peak near 2.3 eV should not be a pure CT state but a mixed excitonic state. To model the electronic excitations of H-aggregated PBI multichromophoric oligomers, we adopt a mixed FE-CTE model Hamiltonian, whose microscopic parameters are determined from LRC-DFT/TD-LRC-DFT calculations performed on an individual chromophore or a chromophore pair. By involving four to five PBI chromophores, we have succeeded in reproducing the experimental trends of optical properties in PBI stacking, such as the large blue shift of the absorption band, the mixed FE-CTE nature of the low-energy absorption bands, and the large Stokes shift of emission spectra. The long-range correction on DFT exchange-correlation energy functionals is crucial to correctly evaluate the photophysical characteristics of pi-pi stacks.

Photoblinking dynamics in single calix[4]arene-linked perylene bisimide dimers

We have studied the fluorescence from individual bridge-linked perylene bisimide dimers and observed blinking over three decades in time which reveals a power-law distribution for the ‘off’ times. The time traces featured three distinct levels of intensity which we assign to the dimer, monomer and background level, respectively. Based on the chronological order of the occurence of the intensity levels we grouped the time traces into three categories and come to the conclusion that for one of these groups the blinking behaviour is governed by a mechanism that is reminiscent to Coulomb blockade in semiconductor quantum dots.

Exciton Trapping in π-Conjugated Materials: A Quantum-Chemistry-Based Protocol Applied to Perylene Bisimide Dye Aggregates

Access to excited-state structures and dynamics of pi-chromophor aggregates is needed to understand their fluorescence behavior and the properties of related materials. A quantum-chemistry-based protocol that provides quantitative and qualitative insight into fluorescence spectra has been applied to perylene bisimide dimers and provides excellent agreement with measured fluorescence spectra. Both dispersion and dipol-dipole interactions determine the preferred relative arrangements of the chromophores in ground and excited states of the dimer. An exciton trapping mechanism is identified, which may limit the energy transfer properties of perylene bisimide and other dye materials.

Perylene Bisimide Dimers as Fluorescent “Glue” for DNA and for Base‐Mismatch Detection

Perylene Bisimide Dimers as Fluorescent “Glue” for DNA and for Base‐Mismatch Detection

Synthesis, Spectroscopy and Photoconductivity of Dimeric Perylene Bisimide Pigments

Perylene bisimide dimers of the type shown in the structure below could be synthesized in high yield and purity by condensation of the corresponding monoimide-monoanhydride with diamines. Dimers in which R and X were alkyl, aryl aralkyl and substituted groups were prepared and characterized by absorption and emission spectroscopy. Like the corresponding monomeric bisimides the extent of Π-overlap (manifested in the pigment color) in the solid dimers is dependent on the structure of the terminal R-groups but is even more sensitive to the nature of the X-bridging group. Most notably, xerographic electrical evaluation of model devices showed that dimers in which X was 1,3-propylene generally showed broader visible spectral response and higher photosensitivity than dimers with other bridging groups.