Two-photon absorption spectrum in diazoaromatic compounds

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)This Letter studies the degenerate two-photon absorption (2PA) spectra of three diazoaromatic compounds using Z-scan with fs-pulses. The 2PA spectra exhibit resonant enhancement of the nonlinearity as the excitation approaches the linear absorption. The absence of 2PA to the pi pi* band is related to the weaker donor/acceptor groups, and lower symmetry of diazoaromatic compounds, in agreement with our semi-empirical calculations. The higher magnitude of the 2PA cross-section, in comparison with single azoaromatics, demonstrates the positive effect of increasing conjugation. The decrease of 2PA cross-section with temperature is attributed to thermally induced torsions, which decreases the effective conjugation of diazoaromatic molecules. (C) 2008 Elsevier B.V. All rights reserved.46341794360363Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES