Probing two-photon excitation dynamics using ultrafast laser pulses

We probe the two-photon excitation dynamics of two new dyes, N,N-diphenyl-7-[2-(4-piridinyl) ethenyl]-9,9-di-n-decylfluoren-2-amine (AF50) and (7-(7-benzothiazol-2-yl-9,9-diethylfluoren-2-yl)-9,9,diethylfluoren-2-yl) diphenylamine (AF250) using femtosecond excitation pulses by Z-scan and time-resolved pump-probe absorption measurements. Irradiance dependence of the induced absorption cross-section is linked to linear absorption of the two-photon excited state. The excited state linear absorption cross-section are 1.0 × 10^-17 cm² for AF250 and 2.7 × 10^-17 cm² for AF250. Relaxation of the two-photon excited state follows a complicated path with three distinct relaxation times. The longest ones, 1.6 ns for the AF50 and 1.9 ns for the AF250, are associated with the respective lowest singlet life-times: 2.23 ns and 2.15 ns.