Unprecedented insight into the phototriggered unfolding of a polypeptide has been gained from it multiscale simulation connecting nonadiabatic A initio molecular dynamics to classical molecular dynamics ill it three-stage manner. An intramolecular H-transfer mechanism that saturates one of the S-center dot radicals of the cleaved S-S bridge and thus prevents recyclization has been observed. This chemical quenching mechanism may be the key to resolving the controversy surrounding, the S-S reformation rates.