Linear and Two-Photon Photophysical Properties of a Series of Symmetrical Diphenylaminofluorenes

A series of linear, symmetrical, diphenylaminofluorene-based materials are reported. The series investigated was model 9,9-didecyl-2,7-bis (N,N-diphenylamino)fluorene (1), oligomer 9,9-didecyl -N,N-bis(9,9-didecyl-7-N,N-diphenylaminofluoren-2-yl) -N,N-diphenyl-fluorene-2,7-diamine (2), and poly(9,9didecyl-2,7-diphenylaminofluorene) (3). Structural characterization and photophysical properties, including linear absorption, quantum yields, single photon fluorescence, and two-photon absorption (2PA) spectra, were studied in polar and nonpolar solvents. 2PA spectra were determined by two independent methods: a nonlinear transmission method employing a femtosecond white-light continuum (WLC) and a twophoton fluorescence (2PF) method. Polymer 3, a lowmolecular-weight polymer with fourteen fluorene units, exhibited a very large two-photon absorption crosssection of 17 200 and 6800 × 10-50 cm4 s photon-1 molecule-1 as estimated from the WLC and 2PF methods, respectively.