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(9,9-didecyl-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 two-photon fluorescence (2PF) method. Polymer 3, a low-molecular-weight polymer with fourteen fluorene units, exhibited a very large two-photon absorption cross-section of 17 200 and 6800 × 10 - 50 cm 4 s photon - 1 molecule - 1 as estimated from the WLC and 2PF methods, respectively.