Theoretical study on ultrafast intersystem crossing of chromium(III) acetylacetonate

► Origin of ultrafast intersystem crossing in a chromium complex, CrIII (acac)3. ► Ab initio quantum chemistry and excited-state wavepacket dynamics. Potential energy surfaces of excited states and spin-orbit couplings. ► Duschinsky analysis of Jahn-Teller distortion. ► Potential crossings in the Franck-Condon region cause ultrafast intersystem crossing.