Enhanced triplet formation in polycrystalline tetracene films by femtosecond optical-pulse shaping.
Polycrystalline tetracene films have been explored using weak ∼ 30 fs visible laser pulses that excite the lowest singlet exciton as well as coherent vibrational motion. Transient difference spectra show a triplet absorption which arises following singlet fission (SF) and persists for 1.6 ns without decay. Adaptive pulse shaping identifies multipulse optimal fields which maximize this absorption feature by ∼ 20%. These are comprised of subpulses separated by time delays well correlated with the period of lattice vibrations suggesting such modes control the yield of SF photochemistry.