Perylene Bisimide Aggregates Research Articles

Peptide‐tethered Perylenebisimide Aggregates with Copper Nanoclusters showing Thermoresponsive and Photoresponsive Properties

AbstractA centrally located dipeptide(P) covalently attached to two perylene bisimide units [(PBI)2P] was synthesized and it was used to fabricate a hybrid system by aggregating with blue‐emitting, atomically precise copper nano‐clusters (Cu NCs). The interactions between these components [(PBI)2P] and Cu NCs] was thoroughly investigated by UV‐Vis spectroscopy and field emission gun transmission electron microscopy (FEG‐TEM).The effect of interaction between components on the optical properties of the hybrids was investigated by fluorescence spectroscopy. Interestingly, this hybrid system shows fluorescence thermometric behaviour at the 20–50 °C temperature range with a promising reversible switchable fluorescence property. Photo‐switching property is enhanced significantly in the hybrid compared to that of the peptide tethered pelylene bisimides as it is evident from the improvement of photocurrent gain (Ion/Ioff) from 2.6 in [(PBI)2P] to 6.9 in the hybrid. Modulation of photo‐switching property along with the thermo‐sensitive fluorescence property in this hybrid holds a future promise for fabrication of devices from the peptide based hybrids.

Long-range corrected fragment molecular orbital density functional tight-binding method for excited states in large molecular systems.

Herein, we present a new method to efficiently calculate electronically excited states in large molecular assemblies, consisting of hundreds of molecules. For this purpose, we combine the long-range corrected tight-binding density functional fragment molecular orbital method (FMO-LC-DFTB) with an excitonic Hamiltonian, which is constructed in the basis of locally excited and charge-transfer configuration state functions calculated for embedded monomers and dimers and accounts explicitly for the electronic coupling between all types of excitons. We first evaluate both the accuracy and efficiency of our fragmentation approach for molecular dimers and aggregates by comparing it with the full LC-TD-DFTB method. The comparison of the calculated spectra of an anthracene cluster shows a very good agreement between our method and the LC-TD-DFTB reference. The effective computational scaling of our method has been explored for anthracene clusters and for perylene bisimide aggregates. We demonstrate the applicability of our method by the calculation of the excited state properties of pentacene crystal models consisting of up to 319 molecules. Furthermore, the participation ratio of the monomer fragments to the excited states is analyzed by the calculation of natural transition orbital participation numbers, which are verified by the hole and particle density for a chosen pentacene cluster. The use of our FMO-LC-TDDFTB method will allow for future studies of excitonic dynamics and charge transport to be performed on complex molecular systems consisting of thousands of atoms.

Excimer Formation of Perylene Bisimide Dyes within Stacking-Restrained Folda-Dimers: Insight into Anomalous Temperature Responsive Dual Fluorescence

Excimer Formation of Perylene Bisimide Dyes within Stacking-Restrained Folda-Dimers: Insight into Anomalous Temperature Responsive Dual Fluorescence

Addressing the Frenkel and charge transfer character of exciton states with a model Hamiltonian based on dimer calculations: Application to large aggregates of perylene bisimide.

To understand the influence of interchromophoric arrangements on photo-induced processes and optical properties of aggregates, it is fundamental to assess the contribution of local excitations [charge transfer (CT) and Frenkel (FE)] to exciton states. Here, we apply a general procedure to analyze the adiabatic exciton states derived from time-dependent density functional theory calculations, in terms of diabatic states chosen to coincide with local excitations within a restricted orbital space. In parallel, motivated by the need of cost-effective approaches to afford the study of larger aggregates, we propose to build a model Hamiltonian based on calculations carried out on dimers composing the aggregate. Both approaches are applied to study excitation energy profiles and CT character modulation induced by interchromophore rearrangements in perylene bisimide aggregates up to a tetramer. The dimer-based approach closely reproduces the results of full-aggregate calculations, and an analysis in terms of symmetry-adapted diabatic states discloses the effects of CT/FE interactions on the interchange of the H-/J-character for small longitudinal shifts of the chromophores.

Switching resonance character within merocyanine stacks and its impact on excited-state dynamics

Summary In this study, the optical properties and excited-state dynamics of the unique self-assembled donor-acceptor (DA) merocyanine dye stacks from dimer up to octamer, prepared via dipole-dipole interactions, are reported in terms of coherent exciton dynamics and formation of an excimer-like state. Our findings are based on the steady-state absorption/emission, time-resolved fluorescence, and transient absorption (anisotropy) measurements, including wavepacket analysis and quantum mechanical calculations. Coherent exciton of torsional motions-restricted dye stacks rapidly localizes into the weakly emissive excimer-like state, by shortening the inter-moiety distance and changing the bond-length alternation pattern. The inner merocyanine moiety, having two neighboring units, has a reversed resonance character (non-polar (N) Z) in the ground state. This difference has led to two conclusions: (1) tetramers and octamers exhibit different features of excimer-like state than the dimer, and (2) octamers exhibit slower localization dynamics due to the enhanced homogeneity (six inner-moieties) compared with tetramers (two inner moieties).

Study of the exciton dynamics in perylene bisimide (PBI) aggregates with symmetrical quasiclassical dynamics based on the Meyer-Miller mapping Hamiltonian.

The exciton dynamics in one-dimensional stacked PBI (Perylene Bisimide) aggregates was studied with SQC-MM dynamics (Symmetrical Quasiclassical Dynamics based on the Meyer-Miller mapping Hamiltonian). Based on linear vibronic coupling models, one-dimensional PBI aggregates with different lengths were investigated. Based on an investigation of short PBI aggregates (10 sites and 80-140 modes) using both the SQC-MM and ML-MCTDH (multilayer multiconfigurational time-dependent Hartree) methods, we showed that SQC-MM dynamics give a reasonable description of the exciton dynamics for organic PBI aggregates composed of 101 sites and 808 modes. This allows us to employ SQC-MM dynamics in the explicit study of exciton diffusion for long one-dimensional PBI aggregates based on models with different site-site coupling strengths with/without static disorder by including all the involved electronic and vibrational degrees of freedom.

Ultrafast coherent exciton dynamics in size-controlled perylene bisimide aggregates.

For H-aggregates of perylene bisimide (PBI), it has been reported that upon photoexcitation, an initially delocalized Frenkel exciton is localized by excimer formation. However, in recent studies, the beforehand exciton dynamics preceding the excimer formation was suggested in larger aggregates consisting of at least more than 10-PBI subunits, which was not observed in small aggregates comprising less than four-PBI subunits. This feature implies that the size of molecular aggregates plays a crucial role in the initial exciton dynamics. In this regard, we have tried to unveil the initial exciton dynamics in PBI H-aggregates by tracking down the transient reorientations of electronic transition dipoles formed by interactions between the PBI subunits in systematically size-controlled PBI H-aggregates. The ultrafast coherent exciton dynamics depending on the molecular aggregate sizes can be distinguished using polarization-dependent femtosecond-transient absorption anisotropy spectroscopic measurements with a time resolution of ∼40 fs. The ultrafast decay profiles of the anisotropy values are unaffected by vibrational relaxation and rotational diffusion processes; hence, the coherent exciton dynamics of the PBI H-aggregates prior to the excimer formation can be directly revealed as the energy migration processes along the PBI H-aggregates.

Perylene Bisimide Aggregates as Probes for Subnanomolar Discrimination of Aromatic Biogenic Amines.

Perylene bisimide derivatives show peculiar physical chemical features, such as a highly conjugated system, high extinction coefficients and elevated fluorescence quantum yields, making them suitable for the development of optical sensors of compounds of interest. In particular, they are characterized by the tendency to aggregate into π-π stacked supramolecular structures. In this contribution, the behavior of the PBI derivative N, N'-bis(2-(trimethylammonium)ethylene)perylene bisimide dichloride was investigated both in aqueous solution and on solid support. The electronic communication between PBI aggregates and biogenic amines was exploited in order to discriminate aromatic amines down to subnanomolar concentrations by observing PBI fluorescence variations in the presence of various amines and at different concentrations. The experimental findings were corroborated by density functional theory calculations. In particular, phenylethylamine and tyramine were demonstrated to be selectively detected down to 10-10 M concentration. Then, in order to develop a surface plasmon resonance (SPR) device, PBI was deposited onto a SPR support by means of the layer-by-layer method. PBI was deposited in the aggregated form and was demonstrated to preserve the capability to discriminate, selectively and with an outstanding analytical sensitivity, tyramine in the vapor phase and even if mixed with other aromatic amines.

A model hamiltonian tuned toward high level ab initio calculations to describe the character of excitonic states in perylenebisimide aggregates.

On the example of an aggregate of two perylenebisimide (PBI) molecules the character of the lowest excited electronic states in terms of charge transfer (CT) and Frenkel exciton (FE) configurations is investigated as a function of the intermolecular arrangement. A minimal model Hamiltonian based on two FE and two CT configurations at the frontier-orbitals CIS (FOCIS) level is shown to represent a simple and comprehensible approach providing insight into the physical significance of the model Hamiltonian matrix elements. The recently introduced analysis and diabatization procedure (Liu et al., J. Chem. Phys. 2015, 143, 084106 ) method is used to extract the energies of the configurations and their interactions (the model Hamiltonian parameters) also from the accurate CC2 approach. An analysis in terms of diabatic energy profiles and their interactions shows that the FOCIS parameters give a qualitatively correct description of the adiabatic excited state energy profiles. Comparison with CC2 reveals, however, the presence of avoided crossings at FOCIS level, associated with a large character change (CT/FE) of the excited states as a function of the aggregate structure, which represents the major drawback of FOCIS results. We show that proper amendment of the FOCIS-derived parameters allows to accurately represent the potential energy surfaces and crossings of the excited dimer states as a function of the aggregate structure. © 2018 Wiley Periodicals, Inc.

Regulating morphologies and near-infrared photothermal conversion of perylene bisimide via sequence-dependent peptide self-assembly.

The assembly behavior of perylene bisimide (PBI) can be precisely organised by the conjugation of sequence-dependent di-peptides in aqueous media. The assembled nanostructures and consequent properties of PBI aggregates can be tuned by the use of different peptide sequences with improved yield of radical anions and enhanced photothermal conversion efficiency.

Low temperature exciton dynamics and structural changes in perylene bisimide aggregates

The temperature dependent exciton dynamics of J-aggregates formed by a perylene bisimide dye is investigated down to liquid nitrogen temperature (77 K) by femtosecond pump–probe spectroscopy. The analysis of the transient absorption data using a diffusion model for the excitons does not only reveal an overall decrease of the exciton mobility, but also a change in the dimensionality of the exciton transport at low temperatures. This change in dimensionality is further investigated by kinetic Monte Carlo simulations, identifying weakly interlinked one-dimensional aggregate chains as the most likely structure at low temperatures. This causes the exciton transport to be highly anisotropic.

Reversible helical chirality of perylene bisimide aggregates: amino acid-directed chiral transfer and chiral inversion.

Through the formation of dynamic covalent bonds, we succeeded, for the first time, in achieving a reversible chiral transfer from amino acids to perylene bisimide aggregates in aqueous solutions. Two opposite helical aggregations are induced with l-phenylalanine and l-tyrosine, respectively. It is possible that the change in configurations of phenyl groups in amino acids leads to the chiral inversion of BAPBI arrangements.

Observation of Two-Exciton States in Perylene Bisimide Aggregates

The behavior of excitons on perylene bisimide aggregates is investigated at high excitation densities by femtosecond absorption spectroscopy. Indications for a significant population in the two-exciton manifold are found.

Size-dependent exciton dynamics in one-dimensional perylene bisimide aggregates

The size-dependent exciton dynamics of one-dimensional aggregates of substituted perylene bisimides are studied by ultrafast transient absorption spectroscopy and kinetic Monte-Carlo simulations as a function of the excitation density and the temperature in the range of 25–90 °C. For low temperatures, the aggregates can be treated as infinite chains and the dynamics is dominated by diffusion-driven exciton–exciton annihilation. With increasing temperature the aggregates dissociate into small fragments consisting of very few monomers. This scenario is also supported by the time-dependent anisotropy deduced from polarization-dependent experiments.

Molecular Assemblies of Perylene Bisimide Dyes in Water

Perylene bisimides are among the most valuable functional dyes and have numerous potential applications. As a result of their chemical robustness, photostability, and outstanding optical and electronic properties, these dyes have been applied as pigments, fluorescence sensors, and n-semiconductors in organic electronics and photovoltaics. Moreover, the extended quadrupolar π system of this class of dyes has facilitated the construction of numerous supramolecular architectures with fascinating photophysical properties. However, the supramolecular approach to the formation of perylene bisimide aggregates has been restricted mostly to organic media. Pleasingly, considerable progress has been made in the last few years in developing water-soluble perylene bisimides and their application in aqueous media. This Review provides an up-to-date overview on the self-assembly of perylene bisimides through π-π interactions in aqueous media. Synthetic strategies for the preparation of water-soluble perylene bisimides and the influence of water on the π-π stacking of perylene bisimides as well as the resulting applications are discussed.

Vibronic Spectra of Perylene Bisimide Oligomers: Effects of Intermolecular Charge-Transfer Excitation and Conformational Flexibility

We have recently presented a theoretical study on the temperature-dependent absorption and photoluminescence spectroscopy of rubrene multichromophores by combining the time-dependent long-range-corrected density functional theory with the Frenkel exciton model (Gao; et al. J. Phys. Chem. A2009, 113, 12847). The spectra of rubrene multichromophores up to heptamers have been calculated and the effects of exciton-phonon coupling and temperature on the photophysical properties of both H- and J-aggregated oligomers were addressed. However, in that work the contribution of intermolecular charge-transfer excitons (CTEs) to vibronic spectra was not addressed. Here we take into account the effect of CTEs for the absorption and emission spectra of the aggregated perylene bisimide (PBI) oligomers in order to have a quantitative explanation to the experimental absorption and emission spectra of the PBI dyes. The role of intermolecular CTEs is discussed for different intermolecular orientations and distances. The simulations demonstrate that the contribution of CTEs becomes significant when the intermolecular distance is less than 4.5 Å for the π-π stacked PBI aggregates, and the mixed exciton model is prerequisite to explain the experimentally observed red-shift of the absorption spectra in this case. The large Stokes shift of the emission spectra can be reproduced by our model, and it is induced by the asymmetric nature of the lowest excitonic state of the H-aggregated oligomers. The experimentally observed broad emission bands come from two species with different conformations. As for J-aggregated PBI oligomers, the interactions of FEs induce the red-shift and the increase of the relative intensity of 0-0 peak of the absorption spectra with more aggregated units.

Identification of the mechanism of enhanced exciton interaction in rigidly linked naphthalene dimers

Recently we characterized the low-lying electronic excitations of H-aggregated perylene bisimide (PBI) dyes using the time-dependent long-range-corrected density functional theory (TD-LRC-DFT) and the mixed intramolecular Frenkel exciton (FE) and the intermolecular charge-transfer exciton (CTE) model (F. Pan, F. Gao, W. Z. Liang and Y. Zhao, J. Phys. Chem. B, 2009, 113, 14581.). We found that the dimer absorption follows closely the spectra of PBI aggregates in solution, and demonstrates strong mixing of two kinds of excitons. Here we implement the theoretical approaches to study the electronic excitations of a family of bridged naphthalene dimers. It is found that TD-LRC-DFT reproduces all experimentally observed trends in the absorption profiles. By comparing the results obtained from the popular hybrid exchange-correlation functionals with these from LRC-DFT, we display how the experimentally measured dipole-allowed mixed exciton states of systems are formed. The major terms which contribute to the experimentally measured dimeric splitting are qualitatively identified. Three-dimensional plots of transition charge density help visualize how the excitons couple.

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.

Fluorescent J-Aggregates of Core-Substituted Perylene Bisimides: Studies on Structure−Property Relationship, Nucleation−Elongation Mechanism, and Sergeants-and-Soldiers Principle

A series of highly soluble and fluorescent, at core tetraaryloxy-substituted and in imide positions hydrogen atom containing perylene bisimide (PBI) dyes 1a-e with varying peripheral side chains have been synthesized and thoroughly characterized. The self-assembly of these PBIs has been studied in detail by UV/vis, linear dichroism (LD) and circular dichroism (CD) spectroscopy, and scanning probe microscopy (AFM, STM). These studies revealed that the present PBIs self-assemble into extended double string cables, which consist of two hydrogen-bonded supramolecular polymeric chains of densely packed and strongly excitonically coupled PBI chromophores, providing highly fluorescent J-aggregates. The aggregation strength ("melting" temperature) and the fluorescence properties of these J-aggregates are dependent on the number and chain length of the peripheral alkoxy substituents, thus revealing a structure-property relationship. In contrast to previously reported assemblies of PBIs, for which the aggregation process is described by the isodesmic (or equal K) model, a cooperative nucleation-elongation mechanism applies for the aggregation of the present assemblies as revealed by concentration-dependent UV/vis absorption studies with the chiral PBI 1e, providing equilibrium constants for dimerization (= nucleation) of K(2) = 13 +/- 11 L mol(-1) and for elongation of K = 2.3 +/- 0.1 x 10(6) L mol(-1) in methylcyclohexane (MCH). LD spectroscopic measurements have been performed to analyze the orientation of the monomers within the aggregates. The nonlinearity of chiral amplification in PBI aggregates directed by sergeants-and-soldiers principle has been elucidated by coaggregation experiments of different PBI dyes using CD spectroscopy. The dimensions as well as the molecular arrangement of the monomeric units in assemblies have been explored by atomic force microscopy (AFM) and scanning tunneling microscopy (STM).

Absorption spectroscopy of molecular trimers

Absorption properties of molecular trimers are studied within a model including a single monomer internal vibrational degree of freedom. Upon photoabsorption, three excited electronic states which are coupled excitonically are accessed. Band shapes resulting from different electronic coupling strengths and geometries are analyzed. It is shown that geometric information can be extracted from the band intensities. Taking data recorded for perylene bisimide aggregates as an example, the spectra for monomer, dimer, and trimer systems are compared.