Excited State Structure Determination

The determination of excited state is to obtain the energy of a series of excited states and their oscillator strength, and the corresponding spectrum is a series of isolated lines. The general operation is to broaden each spectral line, and finally add up all the peaks to obtain the final ultraviolet-visible absorption spectrum. By determining the structure of the excited state, we can understand the changes in the geometric structure of the system caused by the electronic excitation, such as the transfer of hydrogen and the large-scale movement of the molecular structure.

Figure 1. Excited-state dynamics and conformation analyses. a The (TD)DFT-based optimized structure of TMTQ in the S0, S1, and T1 states. The core annulene is colored as red. b The carbon-carbon bond length plot for TMTQ. The molecular structure is drawn based on the bond length distribution in the S0 state. c The plot for HOMA and dihedral angle standard deviation values of core annulene. d Schematic illustration for the electronic structures and excited-state aromatization. (Kim, J.; et al. 2019)

Excited State Structure Determination Process

• Ground state structure optimization.
• Excited state determination based on the wave function of the ground state.

Our Services

At Alfa Chemistry, we mainly apply time-dependent density functional theory and semiemperical methods PM3 to determine the structure of excited state. According to various well-designed calculation methods, we provide the following high-quality and rapid services:

1. Time-dependent density functional theory method (TDDFT)

Various details about the structures and properties of materials in electronically excited state can be obtained using the time-dependent density functional theory method.

• TDDFT optimization involving crossover of excited state potential energy surfaces

For many systems, excited states, especially higher-order excited states, are very densely distributed, that is, there are a large number of excited states whose potential energy surfaces are very close to each other. We are capable of performing geometrical optimization of the excited state when the potential energy surface is involved.

• Steepest descent minimization using Natural Transition Orbitals (SDNTO) method

Our scientists propose a novel approach to implement state-tracking, in which we compare the degree of overlap between the states calculated in the current step and the state tracked in the previous step based on the NTO generated by the current step and the previous step to. The one with the greatest degree of overlap is the state that should be tracked at this step.

• B3LYP approximation

At Alfa Chemistry, computational investigations into the excited-state structures have been also performed at B3LYP/6-31G(d), B3LYP/6-31+G(d)//B3LYP/6-31G(d), and Time-dependent/6-311+G(d)//B3LYP/6-31G(d) levels. Inclusion of implicit solvation in the calculations substantially improves the correlation of the energy of the Soret band with experiment. In addition, singlet excited-state geometries are calculated at the TD-B3LYP/SVP and TD-B3LYP/TZVP//TD-B3LYP/SVP levels. Electronic difference density plots are calculated from these geometries, thereby indicating the change of electron density in the singlet excited states.

2. Semiemperical methods (PM3) (Parametric Method 3)

• We are capable of conducting various molecular calculations such as geometry optimization, molecular structure visualization, determination of vibrational frequencies of functional groups to provide molecular building analyses.
• Our PM3 semi-empirical QM parameterization is developed based on the Hartree-Fock calculation method. We use this computer aided geometry optimization method to perform calculation of excited state properties.

Why Choose Alfa Chemistry

• At Alfa Chemistry, we have rich experience in determining the charge transfer excitation and excitation type.
• We fully consider the influence of vibration coupling, solvent effects (equilibrium solvent and non-equilibrium solvent, strong interaction between solvent and solute, etc.), and the overlap between absorption peaks of different transitions on the excited state structure determination.

Excited state structure determination provides an effective way to optimize the chemical process. Our excited state structure determination services remarkably reduce the cost, promote further experiments, and enhance the understanding of chemical process for customers worldwide. Our personalized and all-around services will satisfy your innovative study demands. If you are interested in our services, please don't hesitate to contact us. We are glad to cooperate with you and witness your success!

Reference

• Kim, J.; et al. Two-electron transfer stabilized by excited-state aromatization. Nature Communications. 2019, 10(1).