Nonperturbative analytic approach to the interaction of intense ultrashort chirped pulses with molecules in solution: Picture of “moving” potentials

Chirped Laser Pulse Control of Vibronic Wavepackets and Energy Transfer in Phycocyanin 645

Photosynthetic organisms use light-harvesting complexes to increase the spectrum of light that they absorb from solar photons. Recent ultrafast spectroscopic studies have revealed that efficient (sub-ps) energy transfer is mediated by vibronic coherence in the phycobiliprotein phycocyanin 645 (PC645). Here, we report studies that employ broadband pump-probe spectroscopy with linearly chirped excitation pulses to further investigate the relationship between vibronic state preparation and energy transfer dynamics in PC645. Negatively chirped pulse excitation is found to enhance wavepackets of a high-frequency mode (1580 cm-1) and increase the rate of downhill energy transfer, while on the other hand, positively chirped pulses suppress these oscillatory features and decrease this rate. Model calculations incorporating the influence of the chirped pump pulse are used to understand its effect on initial state preparation. These results provide mechanistic insight into how the overall nonequilibrium rate of energy transfer is influenced by initial state preparation.

Effects of Electron-Vibration Interaction in Polariton Luminescence: Non-Markovian Fano Resonances and Hot Luminescence

We have developed a non-Markovian theory of the polariton luminescence taking the molecular vibrations into account. The calculations were performed in the polariton basis. We have shown that the frequency shift and the polariton spectral line broadening strongly depend on the frequency-dependent exciton contribution to the polariton. In the single-mode microcavity, our non-Markovian theory predicts the Fano resonances in the polariton luminescence and also narrowing of the spectral lines with the increase of the total number of molecules in the case of the intramolecular nature of the low-frequency vibrations. The theory enables us to consider a nonequilibrium (hot) exciton-polariton luminescence similar to the hot luminescence of molecules and crystals. This opens a way for its observation in organic-based nanodevices.

Fluorescence Phenomena in Amyloid and Amyloidogenic Bionanostructures

Nanoscale optical labeling is an advanced bioimaging tool. It is mostly based on fluorescence (FL) phenomena and enables the visualization of single biocells, bacteria, viruses, and biological tissues, providing monitoring of functional biosystems in vitro and in vivo, and the imaging-guided transportation of drug molecules. There is a variety of FL biolabels such as organic molecular dyes, genetically encoded fluorescent proteins (green fluorescent protein and homologs), semiconductor quantum dots, carbon dots, plasmonic metal gold-based nanostructures and more. In this review, a new generation of FL biolabels based on the recently found biophotonic effects of visible FL are described. This intrinsic FL phenomenon is observed in any peptide/protein materials folded into β-sheet secondary structures, irrespective of their composition, complexity, and origin. The FL effect has been observed both in natural amyloid fibrils, associated with neurodegenerative diseases (Alzheimer’s, Parkinson’s, and more), and diverse synthetic peptide/protein structures subjected to thermally induced biological refolding helix-like→β-sheet. This approach allowed us to develop a new generation of FL peptide/protein bionanodots radiating multicolor, tunable, visible FL, covering the entire visible spectrum in the range of 400–700 nm. Newly developed biocompatible nanoscale biomarkers are considered as a promising tool for emerging precise biomedicine and advanced medical nanotechnologies (high-resolution bioimaging, light diagnostics, therapy, optogenetics, and health monitoring).

Extreme and Topological Dissipative Solitons with Structured Matter and Structured Light

Structuring of matter with nanoobjects allows one to generate soliton-like light bundles with extreme characteristics-temporal duration and spatial dimensions. On the other hand, structuring of light gives the possibility to form light bundles with complicated internal structure; their topology could be used for information coding similar to that in self-replicating RNA molecules carrying genetic code. Here we review the both variants of structuring. In the first variant, we consider a linear molecular chain and organic film interacting resonantly with laser radiation. Demonstrated are optical bistability, switching waves, and dissipative solitons, whose sizes for molecular J-aggregates can reach the nanometer range. We also discuss some theoretical approaches to take into account multi-particle interaction and correlations between molecules. In the second variant, light structuring in large-size laser medium with saturable amplification and absorption is achieved by preparation of the initial field distribution with a number of closed and unclosed vortex lines where the field vanishes. Various types of topological solitons, parameter domains of their stability, and transformation of the solitons with slow variation of the scheme parameters are presented.

Controlling S2 Population in Cyanine Dyes Using Shaped Femtosecond Pulses

Fast population transfer from higher to lower excited states occurs via internal conversion (IC) and is the basis of Kasha's rule, which states that spontaneous emission takes place from the lowest excited state of the same multiplicity. Photonic control over IC is of interest because it would allow direct influence over intramolecular nonradiative decay processes occurring in condensed phase. Here we tracked the S2 and S1 fluorescence yield for different cyanine dyes in solution as a function of linear chirp. For the cyanine dyes with polar solvation response IR144 and meso-piperidine substituted IR806, increased S2 emission was observed when using transform limited pulses, whereas chirped pulses led to increased S1 emission. The nonpolar solvated cyanine IR806, on the other hand, did not show S2 emission. A theoretical model, based on a nonperturbative solution of the equation of motion for the density matrix, is offered to explain and simulate the anomalous chirp dependence. Our findings, which depend on pulse properties beyond peak intensity, offer a photonic method to control S2 population thereby opening the door for the exploration of photochemical processes initiated from higher excited states.

Solvation Stokes-Shift Dynamics Studied by Chirped Femtosecond Laser Pulses

The early optical dynamic response, resulting population, and electronic coherence are investigated experimentally and modeled theoretically for IR144 in solution. The fluorescence and stimulated emission response are studied systematically as a function of chirp. The magnitude of the chirp effect on fluorescence and stimulated emission is found to depend quadratically on pulse energy, even where excitation probabilities range from 0.02 to 5%, in the so-called "linear excitation regime". Interestingly, the shape of the chirp dependence on fluorescence and stimulated emission is found to be independent of pulse energy. The chirp dependence reveals dynamics related to solvent rearrangement following excitation and also depends on electronic relaxation of the chromophore. The experimental results are successfully simulated using a four-level model in the presence of inhomogeneous broadening of the electronic transitions.

Adiabatic Passage in a Three-State System with Non-Markovian Relaxation: The Role of Excited-State Absorption and Two-Exciton Processes

The influence of excited-state absorption (ESA) and two-exciton processes on a coherent population transfer with intense ultrashort chirped pulses in molecular systems in solution has been studied. A unified treatment of adiabatic rapid passage (ARP) in such systems has been developed using a three-state electronic system with relaxation treated as a diffusion on electronic potential energy surfaces. We have shown that ESA has a profound effect on coherent population transfer in large molecules that necessitates a more accurate interpretation of experimental data. A simple and physically clear model for ARP in molecules with three electronic states in solution has been developed by extending the Landau-Zener calculations putting in a third level to random crossing of levels. A method for quantum control of two-exciton states in molecular complexes has been proposed.

Minimizing broadband excitation under dissipative conditions

Optimal control theory is employed for the task of minimizing the excited-state population of a dye molecule in solution. The spectrum of the excitation pulse is contained completely in the absorption band of the molecule. Only phase control is studied which is equivalent to optimizing the transmission of the pulse through the medium. The molecular model explicitly includes two electronic states and a single vibrational mode. The other degrees of freedom are classified as bath modes. The surrogate Hamiltonian method is employed to incorporate these bath degrees of freedom. Their influence can be classified as electronic dephasing and vibrational relaxation. In accordance with experimental results, minimal excitation is associated with a negatively chirped pulses. Optimal pulses with more complex transient structure are found to be superior to linearly chirped pulses. The difference is enhanced when the fluence is increased. The improvement degrades when dissipative effects become more dominant.

Coherent population transfer in molecules coupled with a dissipative environment by intense ultrashort chirped pulse. II. A simple model

We have developed a simple and physically clear picture of adiabatic rapid passage (ARP) in molecules in solution by careful examination of all the conditions needed for ARP. The relaxation effects were considered in the framework of the Landau-Zener model for random crossing of levels. The model enables us to include into consideration non-Markovian Gaussian-correlated noise. It explains all the numerical results obtained in the first paper of the series [B. D. Fainberg and V. A. Gorbunov, J. Chem. Phys. 117, 7222 (2002)], in particular, that for positive chirp pulse excitation relaxation favors more efficient population transfer with respect to the relaxation-free system with frozen nuclear motion. We also relate parameters of non-Markovian Gaussian-correlated noise with irreversible dephasing time of an optical transition by calculating the photon echo signal attenuation.