Excitonic coupling in covalently-bound Perylene Bisimide dimers revealed by two-dimensional electronic spectroscopy

Supramolecular structures based on Perylene Bisimides (PBIs) have been extensively studied because of their fundamental photophysical properties and for their application in a range of different optoelectronic devices. Two-dimensional electronic spectroscopy (2D-ES) is the most complete third order (χ(3)) technique, it has been shown that it is particularly useful to disentangle close-lying energy levels and to reveal dynamics in coupled molecular systems. Two different PBI covalently “head-to-tail” bound dimers (D0 and D1) with increasing interchromophoric separation, and a reference monomer (M) were synthesised and studied by means of 2D-ES in order to characterise the 1 to 2-exciton state transition and how its behaviour changes in relation to the PBI-PBI distance

One- to Two-Exciton Transitions in Perylene Bisimide Dimer Revealed by Two-Dimensional Electronic Spectroscopy

The excited-state energy levels of molecular dimers and aggregates play a critical role in their photophysical behavior and an understanding of the photodynamics in such structures is important for developing applications such as photovoltaics and optoelectronic devices. Here, exciton transitions in two different covalently bound PBI dimers are studied by two-dimensional electronic spectroscopy (2DES), a powerful spectroscopic method, providing the most complete picture of vibronic transitions in molecular systems. The data are accurately reproduced using the equation of motion-phase matching approach. The unambiguous presence of one-exciton to two-exciton transitions are captured in our results and described in terms of a molecular exciton energy level scheme based on the Kasha model. Furthermore, the results are supported by comparative measurements with the PBI monomer and another dimer in which the interchromophore distance is increased

Laser Control of Dissipative Two-Exciton Dynamics in Molecular Aggregates

There are two types of two-photon transitions in molecular aggregates, that is, non-local excitations of two monomers and local double excitations to some higher excited intra-monomer electronic state. As a consequence of the inter-monomer Coulomb interaction these different excitation states are coupled to each other. Higher excited intra-monomer states are rather short-lived due to efficient internal conversion of electronic into vibrational energy. Combining both processes leads to the annihilation of an electronic excitation state, which is a major loss channel for establishing high excitation densities in molecular aggregates. Applying theoretical pulse optimization techniques to a Frenkel exciton model it is shown that the dynamics of two-exciton states in linear aggregates (dimer to tetramer) can be influenced by ultrafast shaped laser pulses. In particular, it is studied to what extent the decay of the two-exciton population by inter-band transitions can be transiently suppressed. Intra-band dynamics is described by a dissipative hierarchy equation approach, which takes into account strong exciton-vibrational coupling in the non-Markovian regime.Comment: revised version, fig. 8 ne

Conditional quantum nonlocality in dimeric and trimeric arrays of organic molecules

Arrays of covalently bound organic molecules possess potential for light-harvesting and energy transfer applications due to the strong coherent dipole-dipole coupling between the transition dipole moments of the molecules involved. Here, we show that such molecular systems, based on perylene-molecules, can be considered as arrays of qubits that are amenable for laser-driven quantum coherent control. The perylene monomers exhibit dephasing times longer than four orders of magnitude a typical gating time, thus allowing for the execution of a large number of gate operations on the sub-picosecond timescale. Specifically, we demonstrate quantum logic gates and entanglement in bipartite (dimer) and tripartite (trimer) systems of perylene-based arrays. In dimers, naturally entangled states with a tailored degree of entanglement can be produced. The nonlocality of the molecular trimer entanglement is demonstrated by testing Mermin's (Bell-like) inequality violation.Comment: 14 pages, 8 figures, comments are welcom

Modelling ultrafast two-dimensional spectroscopy of vibronic systems using non-Markovian hierarchical equations of motion.

Two-dimensional spectroscopy utilises a series of ultrafast optical interactions to create excited populations and track the decay of resulting wavepackets. This enables the study of the potential energy surfaces of complex chemical and biological systems, including the rates of relaxation between states and the dephasing of ensembles. But the inherent complexity of the condensed phase, associated with the vast degrees of freedom and disorder, presents significant challenges in modelling such photophysical processes. In particular, the similarity in relaxation timescale of the system and its surrounding environment provides the opportunity for feedback of information, introducing memory effects which have a major impact on the spectral lineshape. The shape and duration of the applied laser pulses also leads to filtering effects, such that spectra of complex systems can easily be misinterpreted. In this research, theoretical models for the simulation of two-dimensional electronic spectroscopy of vibronic systems are developed in both the underdamped and overdamped limits, using the hierarchical equations of motion to account for non-Markovian memory effects. Firstly, an investigation into the origins of spectral broadening from the perspective of quantum information theory finds that underdamped environments involve greater non-Markovian effects, but also that increased inhomogeneous broadening in overdamped environments is correlated with greater measurable non-Markovianity. The role of the laser spectrum is then demonstrated through spectral filtering of the coherence pathways of a vibronic zinc-porphyrin monomer. Changes in the 2D spectra on formation of delocalized exciton states in vibronic dimers are then examined in terms of a series of perylene bisimide homodimers, where the electronic coupling is controlled by increasing the monomer separation distance. Finally, an analysis of vibrational relaxation within a vibronic heterodimer, combined with selective laser excitation, demonstrates the full capability of the model by simulating energy transfer within an excitonic aggregate involving both system and environmental vibrational motion

Time-Dependent Density Matrix Renormalization Group Algorithms for Nearly Exact Absorption and Fluorescence Spectra of Molecular Aggregates at Both Zero and Finite Temperature

We implement and apply time-dependent density matrix renormalization group (TD-DMRG) algorithms at zero and finite temperature to compute the linear absorption and fluorescence spectra of molecular aggregates. Our implementation is within a matrix product state/operator framework with an explicit treatment of the excitonic and vibrational degrees of freedom, and uses the locality of the Hamiltonian in the zero-exciton space to improve the efficiency and accuracy of the calculations. We demonstrate the power of the method by calculations on several molecular aggregate models, comparing our results against those from multi-layer multiconfiguration time- dependent Hartree and n-particle approximations. We find that TD-DMRG provides an accurate and efficient route to calculate the spectrum of molecular aggregates.Comment: 10 figure

GNA as a scaffold for chromophores aggregates and design of silicon-based DNA binders

My work mainly includes two parts, one is GNA as a scaffold for molecular aggregates of chromophores, and the other one is the design of octahedral silicon complexes as DNA binders. In the first part of the thesis, simplified glycol nucleic acid (GNA) was used as the template for the helical assembly of covalently bound homochromophores and heterochromophores: perylene bisimide (B), phthalocyanine (Y), and porphyrin (P), and different numbers of chromophores could be stacking inside a duplex which led to functional artificial double-helical structures. In the second part of the thesis, the first examples of biologically active complexes based on octahedral silicon were designed, and silicon complexes with simple arenediol ligands and phenazinediol ligands were successfully synthesized. These kinds of siliconcomplexes could be used to intercalate with DNA duplexes, detect mismatched DNA base pairs, and stabilize the formation of the G- quadruplex

All-Polymer Photonic Microcavities Doped with Perylene Bisimide J-Aggregates

Thanks to exciting chemical and optical features, perylene bisimide (PBI) J-aggregates are ideal candidates to be employed for high-performance plastic photonic devices. However, they generally tend to form - stacked H-aggregates that are unsuitable for implementation in polymer resonant cavities. In this work, we demonstrate the efficient compatibilization of a tailored perylene bisimide forming robust J-aggregated supramolecular polymers into amorphous polypropylene. The new nanocomposite was then implemented into an all-polymer planar microcavity which provides strong and directional spectral redistribution of the J-aggregate photoluminescence, owing to a strong modification of the photonic states. A systematic analysis of the photoemitting processes, including photoluminescence decay and quantum yields, shows that the optical confinement in the polymeric microcavity does not introduce any additional nonradiative de-excitation pathways to those already found in the J-aggregate nanocomposite film and pave the way to PBI-based high-performance plastic photonic devices