Molecular mechanisms of the photostability of indigo

摘要: The photophysics of indigo as well bispyrroleindigo, the basic chromophore indigo, has been investigated with ab initio electronic-structure calculations. Vertical electronic excitation energies and excited-state potential-energy profiles have calculated CASSCF, CASPT2 CC2 methods. calculations reveal that bispyrroleindigo undergo intramolecular single-proton transfer between adjacent N–H CO groups in 1ππ* excited state. nearly barrierless proton provides pathway for a very efficient deactivation state via conical intersection ground While low-lying S1–S0 exists also after double-proton transfer, latter reaction path exhibits much higher barrier. trans → cisphotoisomerizationvia twisting central CC bond bispyrroleindigo. It found is unlikely to play role photochemistry because large barrier rather high energy twisted structure. These findings indicate exceptional photostability result rapid internal conversion combined absence low-barrier generation cis isomer cisphotoisomerization.