Broadband Multiphoton Upconversion Fluorescence of Novel Dendrimers by a Femtosecond Ti:Sapphire Laser

The multiphoton absorption and multi-photon-excited upconversion fluorescence of dendrimers, 1,2,4,5-tetra(4-N,N-diphenylaminostyryl) benzene (TPAB), 1,2,4,5-tetra [4-N, N-di (4-bromophenyl) aminostyryl] benzene (TPAB-Br) and 1, 2, 4, 5-tetra {4-{N,N-bis{4-{4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2 -yl]styryl}phenyl} amino styryl} benzene (TPAB-OXA), were measured by a femtosecond Ti: sapphire laser. The absorption, fluorescence emission and fluorescence lifetime of these octupolar chromophores were investigated. Pumped by a femtosecond laser at 1300 nm and 800 nm, strong upconversion fluorescence were observed. The maximum peaks of two-photon fluorescence in the solution of CH2Cl2 are at 569 nm for TPAB, at 535 nm for TPAB-Br and at 621 nm for TPAB-OXA, respectively. The three-photon excited fluorescence with the central wavelength at 566 nm for TPAB, at 534 nm for TPAB-Br and at 610 nm for TPAB-OXA in the solution of CH2Cl2 were observed. The two-photon absorption cross-section of chromophores obtained by nonlinear transmission method was 61.86 x 10(-50) cm(4).s/photon for TPAB and 65. 98 x 10(-50)cm(4).s/photon for TPAB-OXA in the solution of THF. Large optical power limiting was demonstrated for the octupolar chromophores. Their three-photon absorption coefficients of 1300 nm in THF were 3.88 x 10(-79), 7.76 x 10(-79) and 27.17 x 10(-79) cm(6).s(2), respectively. The dendrimers displayed large multi-photon absorption and strong upconversion fluorescence properties.