Effects Of Charge-transfer States Research Articles

Effect of charge-transfer states on the vibrationally resolved absorption spectra and exciton dynamics in ZnPc aggregates: Simulations from a non-Makovian stochastic Schrödinger equation.

The vibrationally resolved absorption spectra of zinc phthalocyanine (ZnPc) aggregates (up to 70 monomers) are explored using the non-Markovian stochastic Schrödinger equation. Various types of local excitations, charge-transfer (CT) excitations, and exciton-phonon couplings are explicitly included in a comprehensive model Hamiltonian, which is parameterized by first-principles calculations. The absorption spectral simulations clarify that the two absorption bands in the Q-band region observed in experiments can be assigned to the contribution from the CT-mediated interactions, rather than the mixtures of different-type aggregates, as prevailingly assumed. Furthermore, the relative intensities of the two bands are found to be closely related to the intermolecular distance and molecular number in a ZnPc aggregate. From the investigation of the decoherence process after optical excitation, it is found that CT states can induce coherence regeneration as the time scale of charge separation is much faster than that of the vibration-induced decoherence. However, they would instead boost the decoherence process as the two time scales become comparable. The two different effects of CT states may suggest a novel way to regulate the decoherence process in excitation energy relaxation.

Effects of Charge Transfer State and Exciton Migration on Singlet Fission Dynamics in Organic Aggregates

A time-dependent wavepacket diffusion method is used to investigate the effects of charge transfer (CT) states, singlet exciton, and multiexciton migrations on singlet fission (SF) dynamics in organic aggregates. The results reveal that the incorporation of CT states can result in SF dynamics different from the direct interaction between singlet exciton and multiexciton, and an obvious SF interference is also observed between the direct channel and the indirect channel mediated by CT states. In the case of direct interaction, although the fast population transfer of singlet exciton in monomers, caused by the increase of exciton–exciton interaction, can accelerate the SF process, the spatial coherence alternatively has a counter-productive effect, and their competition leads to an optimal exciton–exciton interaction at which SF has a maximal rate. This trade-off relationship in SF dynamics is further analyzed from different perspectives, specifically in spatial and energy representations, and is also confi...

The effect of charge transfer state on the open-circuit voltage of small-molecular organic photovoltaic devices: A comparison between the planar and bulk heterojunctions using electroluminescence characterization

This work studies the open-circuit voltage (VOC) of planar and bulk heterojunction organic photovoltaic (OPV) devices by means of electroluminescent (EL) technique to resolve the charge transfer (CT) states between donor and acceptor. The OPV devices containing a small part of bulk heterojunction increases the VOC as a result of the enhanced CT process as compared with a complete planar structure. Red shift of the CT charge transfer was observed by increasing the bulk volume, which indicates the increased degree of interaction between both molecules and excitons. By characterizing the EL spectra of OPV devices and relating them to the CT absorption, the interfacial property between the donor and acceptor is shown to be crucial for determining the VOC in small-molecule OPV devices. Detailed analysis of the energetic loss was also used to interpret the VOC under the effect of CT states.

Ligand hyperfine coupling in Mo(V) oxyhalide complexes

For a series of Mo(V) oxyhalide complexes MoOL52− (L = F, Cl, Br, I), interpretation of the ligand hyperfine coupling parameters (AL tensor components) is considered. The role of spin polarization is elucidated and the effect of charge transfer states is taken into account. The AL tensor components were calculated using the covalency parameters derived from experimental EPR and optical spectroscopy data for compounds under study (inverse problem of EPR spectroscopy).

Interpretation of the Parameters of the EPR Spectra of Transition Metal Complexes

The calculated parameters of the EPR spectra of complexes of d1 and d9 ions were presented. The covalent bond parameters used in the calculations were determined from EPR and experimental optical data (inverse problem of EPR spectroscopy). Various contributions to the expressions for the EPR parameters were compared. The observed abnormal values of the EPR parameters were discussed. The effects of charge-transfer states and the vibronic coupling on the components of g, A, and AL tensors were considered. Mechanisms of spin density transfer to ligands in paramagnetic complexes were proposed.

Theoretical formulation of the effects of charge transfer states on optical transitions in s2ions

In an attempt to include the effects of charge transfer states into the existing theory for optical transitions in ions embedded in an alkali halide matrix and possessing a closed s2 outer electron shell, group theoretical arguments are employed in order to provide the simplest possible generalization of the existing theory whilst introducing the minimum number of new parameters necessary for its description. Expressions are developed which permit not only an experimental estimate of these new parameters, but also show their utility in accounting for known experimental results which appear anomalous in terms of the existing theoretical structure. Finally further experiments are suggested on specified impurity ion systems in which the advantages of the present formulation over that previously adopted can be subjected to experimental investigation.