The University of Osaka · Materials Science
Professor Ryohei Kishi's research lab specializes in theoretical and computational quantum chemistry, focusing on the electronic structures and nonlinear optical properties of open-shell and diradical systems. The lab investigates singlet diradicals, π-conjugated systems, and excited-state phenomena using advanced quantum chemical methods such as spin-flip configuration interaction, long-range-corrected density functional theory, and finite-field approaches. A key research direction involves understanding the relationship between diradical character and nonlinear optical responses, particularly second hyperpolarizabilities (γ), in complex organic systems. The lab also explores the synthesis and electronic properties of novel carbon-rich architectures, such as periazulene-based macrocycles, combining theory with experimental collaboration.
Figures are computed from collected data and may differ slightly.
Within the spin-unrestricted density functional theory (DFT) the long-range correction (LC) scheme combined with the Becke-Lee-Yang-Parr exchange-correlation functional, referred to as LC-UBLYP method, has been applied to the calculation of the second hyperpolarizability (gamma) of open-shell singlet diradical systems of increasing complexity and has demonstrated good performance: (i) for the simplest H(2) dissociation model, the gamma values calculated by the LC-UBLYP method significantly overs
Bis-periazulene (cyclohepta[<i>def</i>]fluorene), which is an unknown pyrene isomer, was synthesized as kinetically protected forms. Its triaryl derivatives <b>1c</b>-<b>e</b> exhibited the superimposed electronic structures of peripheral, polarized, and open-shell π-conjugated systems. In contrast to previous theoretical predictions, bis-periazulene derivatives were in the singlet ground state. Changing an aryl group controlled the energy gap between the lowest singlet-triplet states.
Ab initio spin-flip configuration interaction (SF-CI) methods with the finite-field (FF) scheme are applied to the calculation of static second hyperpolarizabilities (γ) of several singlet diradical systems, i.e., the model H2 molecule under dissociation, p-quinodimethane, o-quinoid five-membered ring, and 1,4-bis(imidazole-2-ylidene)cyclohexa-2,5-diene (BI2Y) models. The SF-CI method using the UHF reference wave function provides the qualitatively correct diradical character (y) dependence of γ
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