Abegao, Luis M. G.
Cocca, Leandro H. Z.
Mendonca, Cleber R.
Vivas, Marcelo G.
De Boni, Leonardo
Total Authors: 9
 Univ Sao Paulo, Inst Fis Sao Carlos, Photon Grp, CP 369, BR-13560970 Sao Carlos, SP - Brazil
 Univ Fed Goias, Inst Fis, Grp Foton, BR-74690900 Goiania, Go - Brazil
 Univ Lyon, Ens Lyon, CNRS UMR 5182, Lab Chim, F-69342 Lyon - France
 Univ Fed Alfenas, Lab Espectroscopia Otica & Foton, BR-37715400 Pocos De Caldas, MG - Brazil
Total Affiliations: 4
Physical Chemistry Chemical Physics;
Web of Science Citations:
Fluorene-based molecules exhibit significant nonlinear optical responses and multiphoton absorption in the visible region, which, combined with the high fluorescence quantum yield in organic solvents, could make this class of materials potentially engaging in diverse photonics applications. Thus, herein, we have determined the two-photon absorption (2PA) of oligofluorenes containing three, five, and seven repetitive units by employing the wavelength-tunable femtosecond Z-scan technique. Our outcomes have shown that the 2PA cross-section in oligofluorenes presents an enhanced value of around 18 GM per N-eff, in which N-eff is the effective number of pi-electrons, for the pure 2PA allowed transition (1(1)A(g)-like -> 2(1)A(g)-like). Furthermore, a weak 2PA transition was observed in the same spectral region strongly allowed by one-photon absorption (1(1)A(g)-like -> 1(1)B(u)-like). This last result suggests a molecular symmetry perturbation, probably induced by the molecular disorder triggered by the increase of moieties in the oligofluorene structure. We have calculated the permanent dipole moment difference related to the lowest-energy transition using the Lippert-Matagaformalism and the 2PA sum-over-states approach to confirm this assumption. Moreover, we have estimated the fundamental limits for the 2PA cross-section in oligofluorenes. (AU)