The impact of the pi-electron conjugation length on the three-photon absorption cross section of fluorene derivatives

摘要

The three-photon absorption cross sections of three different fluorene derivatives,with extended pi-electron conjugation lengths was experimentally measured and compared with shorter pi-electron conjugation length analogs.The effect of the conjugation length on the three-photon absorption cross section sigma'_3 of this family of molecules has been elucidated.It is demonstrated that sigma'_3 of the asymmetric compound D-pi-pi-pi-A is 6.6 times larger than its shorter configuration D-pi-A,while for the symmetric compounds D-pi-pi-pi-D and A-pi-pi-pi-A a two-fold enhancement was found relative to their shorter conjugation length analogs.Measurements of the three-photon excitation of these compounds in THF solution (10~(-3) M) were accomplished with a tunable optical pulse generation pumped by a 25 ps Nd-YAG laser.