Transient visible absorption in infrared saturable absorbing dyes

An optically generated transient absorbing state in the polymethine pyrylium dyes EK 9860 and 9740 is described. The broadband absorption is produced when solutions of the dyes are irradiated by a 1060 nm picosecond duration pulse. The absorbing state spans the wavelength range from ∼520 to ≳800 nm and is characterized by a molar extinction coefficient of ∼1×104 and by a decay time as short as 13.4 psec (in 9860). The latter result and the 7 psec value previously reported for the recovery of ground state absorption at 1060 nm following excitation at the same wavelength are accommodated by a three level relaxation mechanism. This approach treats the visible absorption as arising from electronic transitions both from the first excited singlet state and from a transient intermediate level. Lack of structure in the transient visible absorption indicates that the transition populates high density bound state manifolds or continuum states.