Two symmetrical fluorene derivatives with diphenylamino and carbazolyl as terminal group have been synthesized, which are named 2,7-bis(N,N-diphenylamino)-9,9-diethyl-fluorene (abbreviated to DPDEF) and 2,7-dicarbazol-9'-yl-9,9-diethyl-fluorene (abbreviated to DCDEF). Their crystal structures were determined by four-circle X-ray diffraction. DPDEF belongs to monoclinic system, C2/c space group, a=2.8649(4) nm, b=0.85111(9) nm, c=2.7012(4) nm, β=100.982(11)°, V=6.4657(14) nm³, Z=8, D_c=1.144 g·cm^-3, R=0.0581. DCDEF belongs to monoclinic system, P2_1/c space group, a=0.92794(12) nm, b=0.88561(9) nm, c=3.7236(4) nm, β=96.914(9)°, V=3.0378(6) nm³, Z=4, D_c=1.208 g·cm^-3, R=0.0652. The fluorene bridge shows perfect planarity with very small dihedral angle (3.0° for DPDEF and 5.8° for DCDEF respectively) between two involved phenyls. Pumped by 730 nm laser pulses, DPDEF exhibited strong blue up-converted fluorescence (λ_max=418 nm) in THF with the two-photon absorption cross-section of 15 GM.

Key words: DPDEF, DCDEF, fluorene derivative, blue up-converted fluorescence