No abstract

The degree of mixing and surface coverage in Langmuir−Blodgett (LB) films of ytterbium bisphthalocyanine (YbPc2) mixed with stearic acid (SA) has been probed using atomic force microscopy (AFM) and micro-Raman imaging. The morphologies extracted for LB films at the nanometer (AFM) and micrometer (micro-Raman) scales are consistently in good agreement. The results show that a 5-layer mixed LB film with 75/25% YbPc2/SA (relative content by weight) displays smaller and more homogeneous distribution of aggregates compared with a 5-layer mixed film of 25/75% YbPc2/SA. Raman microscopy of neat LB films of ytterbium bisphthalocyanine (YbPc2) and mixed YbPc2/stearic acid LB films deposited on glass and silver islands is reported. Resonance Raman scattering (RRS), surface-enhanced resonance Raman scattering (SERRS), and surface-enhanced Raman scattering (SERS) were obtained using laser lines at 633 and 780 nm. The enhanced (SERRS) and unenhanced (RRS) resonance Herzberg−Teller spectra of neat YbPc2 LB films and mixed LB films excited with the 633 nm line are identical.

In this work, we investigate the nonlinear absorption dynamics of Zn phthalocyanine in dimethyl sulfoxide (DMSO). We used single pulse and pulse train Z-scan techniques to determine the dynamics and absorption cross-sections of singlet and triplet states at 532 nm. The excited singlet state absorption cross-section was determined to be 3.2 times higher than the ground state one, giving rise to reverse saturable absorption. We also observed that reverse saturable absorption occurs from the triplet state, after its population by intersystem crossing, whose characteristic time was determined to be 8.9 ns. The triplet state absorption cross-section determined is 2.6 times higher than the ground state one. In addition, we used the white light continuum Z-scan to evaluate the singlet excited state spectrum from 450 to 710 nm. The results show two well-defined regions, one above 600 nm, where reverse saturable absorption is predominant. Below 600 nm, we detected a strong saturable absorption. A three-energy-level diagram was used to explain the experimental results, leading to the excited state absorption cross-section determination from 450 nm up to 710 nm.