Solvent Tuning Excited State Structural Dynamics in a Novel Bianthryl

Electric dipole moment of excited octupolar molecules: Potential qubit implementation

The first excited state of conjugated donor-acceptor molecules of C3 symmetry (octupolar molecules) is doubly degenerate. Such a doublet is known to be isomorphic to a spin 1/2. It is shown that a large electric dipole moment is associated with this spin. Since the mean value of the electric dipole moment of an octupolar molecule is a measure of the symmetry breaking charge transfer, a dimensionless dipole moment called the dissymmetry vector is introduced. The dissymmetry vector operator is constructed. A linear tensor connection between this operator and the Pauli matrices is found. The tensor character is due to the two-dimensionality of the dipole moment. The dipole moment can rotate freely in the plane of the molecule as long as the C3 symmetry is maintained. The rotation is associated only with the rearrangement of the electronic subsystem of the molecule and does not affect the spatial position of the nuclei. This opens up the possibility of changing the dipole moment state on a subpicosecond time scale. The Jahn-Teller effect on the dissymmetry vector is considered in detail. It is shown that the dissymmetry vector can be controlled using electric fields in the same way as three-dimensional spin if both static and alternating electric fields are in the plane of the molecule. The conducted studies indicate that the dipole moment of excited octupolar molecules is a promising candidate for the physical implementation of a qubit.

Distance-Dependent Symmetry-Breaking Charge Transfer in 9,10- Bis(phenylethynyl)anthracene Dimers

To investigate the effect of the through-bond coupling strength on the symmetry-breaking charge separation (SB-CS) dynamics and mechanism, three 9,10-bis((4-hexylphenyl)ethynyl)anthracene dimers with varying distances, viz., a single-bond linked dimer (0-dimer), a phenylene linked dimer (1-dimer) and a para-biphenylene linked dimer (2-dimer), were synthesized and studied systematically using steady-state and transient spectroscopy. Steady-state absorption spectra revealed that the electronic coupling strength decreased gradually with the increase of the inter-chromophore distance, and the transition of S0→S1 includes the dark charge transfer (CT) excitation. fs-TA spectra demonstrated that SB-CS could be conducted in both weakly and highly polar solvents for 0-dimer, but the SB-CS dynamics has a significant difference. In weakly polar solvents, SB-CS only produces the partial CT (PCT) state, but it could generate the CT state via the PCT state in highly polar solvent. In comparison, SB-CS is only proceeded in highly polar solvents in 1-dimer and 2-dimer to produce the CT state directly. These results demonstrate that the SB-CS dynamics is strongly dependent on the inter-chromophore electronic coupling, and the relatively strong electronic coupling is crucial for the occurrence of SB-CS in weakly polar environment that is commonly presented in photoelectric devices.

Controlling the symmetry breaking charge transfer extent in excited quadrupolar molecules by tuning the locally excited state

The effect of a locally excited state on charge transfer symmetry breaking (SBCT) in excited quadrupolar molecules in solutions has been studied. The interaction of a locally excited state and two zwitterionic states is found to either increase or decrease the degree of SBCT depending on the molecular parameters. A strategy on how to adjust the molecular parameters to control the extent of SBCT is presented. The influence of level degeneracy on SBCT is identified and discussed in detail. The level degeneracy is shown to lead to the existence of a hidden dipole moment in excited quadrupolar molecules. Its manifestations in SBCT are analyzed. The main conclusions are consistent with the available experimental data.