Intermolecular Electronic Excitation Transfer in a Confined Space: A First-Principles Study (original) (raw)
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Journal of Physical Chemistry B, 2006
Host-guest materials containing strongly fluorescent donor and acceptor molecules have been prepared. Finetuning of the donor to acceptor distance in this material allows beautiful visible and quantitative observation of electronic excitation energy transfer phenomena. Oxonine and pyronine have been used as guest molecules and zeolite L as host. The dyes have been inserted by ion exchange. Stationary state and time-resolved experiments have been carried out with zeolite crystals of 300 and 700 nm size in the dye concentration range of 10-4 mol/L up to 0.042 mol/L. The fluorescence decay of the donor and the pumping of the acceptor via energy transfer, which can be well observed, became faster with increasing loading. The behavior of the system follows requirements expected for Förster energy transfer material.
Transfer of Electronic Excitation Energy between Dye Molecules in the Channels of Zeolite L
The Journal of Physical Chemistry B, 1998
Host-guest materials containing strongly fluorescent donor and acceptor molecules have been prepared. Finetuning of the donor to acceptor distance in this material allows beautiful visible and quantitative observation of electronic excitation energy transfer phenomena. Oxonine and pyronine have been used as guest molecules and zeolite L as host. The dyes have been inserted by ion exchange. Stationary state and time-resolved experiments have been carried out with zeolite crystals of 300 and 700 nm size in the dye concentration range of 10 -4 mol/L up to 0.042 mol/L. The fluorescence decay of the donor and the pumping of the acceptor via energy transfer, which can be well observed, became faster with increasing loading. The behavior of the system follows requirements expected for Förster energy transfer material.
Orientational Effects in Intra- and Intermolecular Long Range Excitation Energy Transfer
Annals of the New York Academy of Sciences, 1981
FIGURE 2. The probability densityp(K2) as a function of K', where K' is the orientation factor between two transition dipoles, each of which can adopt any orientation, independently of the other. P(K') is the probability distribution for K' being between zero and K'. The probability of K' being less than 0.1, for instance, is seen to be 0.25 for this model.
Molecular Crystals and Liquid Crystals, 2020
The peculiarities of electronic and vibronic excitations transfer processes in polymers and hybrid nanosystems were examined. It is shown, that at distances less 15-25 Å the probability of electronic singlet and triplet excitation energy transfer is rather high and is close to unity. For the singlet-singlet energy transfer between neighbor p-electron-containing macromolecular cells the phenomenon is explained by essential contribution of an exchange mechanism. A similar effect for hybrid functional nanosystems (that were designed for photodynamic therapy) was observed. The manifestations of vibronic excitation transfer along polymer chain were also studied. The critical distance for vibronic excitation transfer jump was estimated as 3-6 Å.
Molecules
The comprehensive characterization of Intramolecular Charge Transfer (ICT) stemming in push-pull molecules with a delocalized π-system of electrons is noteworthy for a bespoke design of organic materials, spanning widespread applications from photovoltaics to nanomedicine imaging devices. Photo-induced ICT is characterized by structural reorganizations, which allows the molecule to adapt to the new electronic density distribution. Herein, we discuss recent photophysical advances combined with recent progresses in the computational chemistry of photoactive molecular ensembles. We focus the discussion on femtosecond Transient Absorption Spectroscopy (TAS) enabling us to follow the transition from a Locally Excited (LE) state to the ICT and to understand how the environment polarity influences radiative and non-radiative decay mechanisms. In many cases, the charge transfer transition is accompanied by structural rearrangements, such as the twisting or molecule planarization. The possib...
Nonadiabatic Excited-State Molecular Dynamics: Modeling Photophysics in Organic Conjugated Materials
Accounts of Chemical Research, 2014
CONSPECTUS: To design functional photoactive materials for a variety of technological applications, researchers need to understand their electronic properties in detail and have ways to control their photoinduced pathways. When excited by photons of light, organic conjugated materials (OCMs) show dynamics that are often characterized by large nonadiabatic (NA) couplings between multiple excited states through a breakdown of the Born−Oppenheimer (BO) approximation. Following photoexcitation, various nonradiative intraband relaxation pathways can lead to a number of complex processes. Therefore, computational simulation of nonadiabatic molecular dynamics is an indispensable tool for understanding complex photoinduced processes such as internal conversion, energy transfer, charge separation, and spatial localization of excitons. Over the years, we have developed a nonadiabatic excited-state molecular dynamics (NA-ESMD) framework that efficiently and accurately describes photoinduced phenomena in extended conjugated molecular systems. We use the fewest-switches surface hopping (FSSH) algorithm to treat quantum transitions among multiple adiabatic excited state potential energy surfaces (PESs). Extended molecular systems often contain hundreds of atoms and involve large densities of excited states that participate in the photoinduced dynamics. We can achieve an accurate description of the multiple excited states using the configuration interaction single (CIS) formalism with a semiempirical model Hamiltonian. Analytical techniques allow the trajectory to be propagated "on the fly" using the complete set of NA coupling terms and remove computational bottlenecks in the evaluation of excited-state gradients and NA couplings. Furthermore, the use of state-specific gradients for propagation of nuclei on the native excited-state PES eliminates the need for simplifications such as the classical path approximation (CPA), which only uses ground-state gradients. Thus, the NA-ESMD methodology offers a computationally tractable route for simulating hundreds of atoms on ∼10 ps time scales where multiple coupled excited states are involved. In this Account, we review recent developments in the NA-ESMD modeling of photoinduced dynamics in extended conjugated molecules involving multiple coupled electronic states. We have successfully applied the outlined NA-ESMD framework to study ultrafast conformational planarization in polyfluorenes where the rate of torsional relaxation can be controlled based on the initial excitation. With the addition of the state reassignment algorithm to identify instances of unavoided crossings between noninteracting PESs, NA-ESMD can now be used to study systems in which these so-called trivial unavoided crossings are expected to predominate. We employ this technique to analyze the energy transfer between poly(phenylene vinylene) (PPV) segments where conformational fluctuations give rise to numerous instances of unavoided crossings leading to multiple pathways and complex energy transfer dynamics that cannot be described using a simple Forster model. In addition, we have investigated the mechanism of ultrafast unidirectional energy transfer in dendrimers composed of poly(phenylene ethynylene) (PPE) chromophores and have demonstrated that differential nuclear motion favors downhill energy transfer in dendrimers. The use of native excited-state gradients allows us to observe this feature.
Electronic Excitations of a Single Molecule Contacted in a Three-Terminal Configuration
Nano Letters, 2007
Low-temperature three-terminal transport measurements through a thiol end-capped Pi -conjugated molecule have been carried out. Electronic excitations, including zero and finite-bias Kondo-effects have been observed and studied as a function of magnetic field. Using a simplified two-orbital model we have accounted for the spin and the electronic configuration of the first four charge states of the molecule. The charge-dependent couplings to gate, source and drain electrodes suggest a scenario in which charges and spins are localized at the ends of the molecule, close to the electrodes.
Excitation dynamics and relaxation in a molecular heterodimer
Chemical Physics, 2012
The exciton dynamics in a molecular heterodimer is studied as a function of differences in excitation and reorganization energies, asymmetry in transition dipole moments and excited state lifetimes. The heterodimer is composed of two molecules modeled as two-level systems coupled by the resonance interaction. The system-bath coupling is taken into account as a modulating factor of the energy gap of the molecular excitation, while the relaxation to the ground state is treated phenomenologically. Comparison of the description of the excitation dynamics modeled using either the Redfield equations (secular and full forms) or the Hierarchical quantum master equation (HQME) is demonstrated and discussed. Possible role of the dimer as an excitation quenching center in photosynthesis selfregulation is discussed. It is concluded that the system-bath interaction rather than the excitonic effect determines the excitation quenching ability of such a dimer.