Unveiling Controlling Factors of the S₀/S₁ Minimum Energy Conical Intersection: A Theoretical Study

Abstract

The minimum energy conical intersection (MECI) geometries play an important role in photophysics and photochemistry. Although a number of MECI geometries can be identified using quantum chemical methods, their chemical interpretation remains unclear. In this study, a systematic analysis was performed on the MECIs between the singlet (S0) and lowest singlet excited (S1) states of organic molecules. The frozen orbital analysis (FZOA), which approximates the excited states with minimal main configurations, was adopted to analyze the excitation energy components at the S0/S1 MECI geometries as well as the S0 and S1 equilibrium geometries. At the S0/S1 MECI geometries, the HOMO–LUMO gaps decreased as expected but did not disappear. The remaining gaps were balanced with the HOMO–LUMO Coulomb integrals. Furthermore, we discovered that the HOMO–LUMO exchange integrals became approximately zero. On the basis of this fact, a systematic interpretation of the S0/S1 MECI geometries has been described.

Spin‐flip approach within time‐dependent density functional tight‐binding method: Theory and applications

“…The SF‐TDDFTB and SF‐TDLCDFTB methods drastically reduced the computational cost with improved accuracy for MECI structures compared with SF‐TDDFT. Furthermore, as shown in our previous study obtained by SF‐TDDFT, the SF‐TDDFTB and SF‐TDLCDFTB calculations indicated the controlling factors, that is, K HL ≈ 0 at S 0 / S 1 MECIs.…”

“…Finally, we verified the controlling factors of S 0 / S 1 MECI discovered in our previous studies at the SF‐TDDFTB and SF‐TDLCDFTB levels. Figure shows the HOMO−LUMO exchange integral, K HL , of Equation in hartree for S 0 EQ and S 0 / S 1 MECI structures of 29 molecules.…”

“…Figure a,b show the results of the SF‐TDDFTB and SF‐TDLCDFTB calculations, respectively. As shown in our previous studies obtained by SF‐TDDFT, the SF‐TDDFTB and SF‐TDLCDFTB calculations indicated the controlling factors, that is, K HL ≈ 0 at S 0 / S 1 MECIs. The average values of K HL obtained from SF‐TDDFTB and SF‐TDLCDFTB calculations at S 0 / S 1 MECIs were 0.0004 and 0.0003 hartree, respectively.…”

“…In our previous study, we discovered controlling factors for S 0 / S 1 MECI structures, which were obtained using frozen orbital analysis (FZOA) . This subsection provides a formalism of the controlling factors in SF‐TDDFTB and SF‐TDLCDFTB methods.…”

Principles of Aggregation‐Induced Emission: Design of Deactivation Pathways for Advanced AIEgens and Applications

“…Thus, non‐radiative decay pathways of AIEgens can be classified according to the deformation of their building blocks. The structures of the CIs of small molecules are classified into several types, which include ring puckering, torsions of double bonds, and ring openings . In fact, some mechanisms of AIEgens have been reported that are based on a coordinate including double bond torsion and ring puckering.…”