Interpreting Strong Two-Photon Absorption of PE3 Platinum Acetylide Complex: Double Resonance and Excited State Absorption

Author(s)

Vivas, Marcelo G. ^{[1, 2]} ; De Boni, Leonardo ^[2] ; Cooper, Thomas M. ^[3] ; Mendonca, Cleber R. ^[2]

Affiliation

^[1] Univ Fed Alfenas, Inst Ciencia Tecnol, BR-37715400 Pocos De Caldas, MG - Brazil

^[2] Univ Sao Paulo, Grp Foton, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP - Brazil

^[3] Air Force Res Lab, Mat & Mfg Directorate, Dayton, OH 45433 - USA

• Document type: Journal article
• Source: ACS PHOTONICS; v. 1, n. 2, p. 106-113, FEB 2014.
• Web of Science Citations: 16

Abstract

This paper reports on the strong two-photon absorption (2PA) of the trans-Pt(PBu3)(2)(C C-C6H4-C C-C6H4-C C-C6H5)(2) (PE3) platinum acetylide complex dissolved in dichloromethane in the visible and near-infrared region. The 2PA spectrum was measured though the open-aperture Z-scan technique using an amplified femtosecond laser system (150 fs) operating at low repetition rate (1 kHz). Since PEs present short intersystem crossing time (ps) and long phosphorescence time (mu s), the 2PA cross-section obtained from the Z-scan technique may have contribution from the triplet states. However, we show by a rate equations model and pump-probe experiments that the rate of population transferred to the triplet state via 2PA, employing a 150 fs laser, and low repetition is negligible (<1%). Consequently, 2PA cross-section from tens to thousands of GM units, observed along the nonlinear spectrum, is due to pure singlet-singlet transitions. Our results also reveal that the 2PA spectrum of PE3 in dichloromethane exhibits two 2PA allowed bands centered at 760 nm (120 GM) and 610 nm (680 GM) and is very intense for wavelengths below of 500 nm (>1000 GM). The first 2PA band was attributed to the S-0 -> S-1 (1(1)Ag-like -> 1(1)Bu-like) transition, which is made possible because of a relaxation of the selection rules for PE3 that, in solution, present centrosymmetric and noncentrosymmetric conformers. The second 2PA band was ascribed to the S-0 -> S-2 (1(1)Ag-like -> 3(1)Ag-like) transition strongly 2PA allowed characteristic in PE's chromophores. On the other hand, the sizable 2PA cross-section observed for the region 460-500 nm was ascribed to a double resonance effect and high singlet excited state absorption (S-0 -> S-n). (AU)

• FAPESP's process: 11/12399-0 - Femtosecond pulses applied to nonlinear optics: spectroscopy, pulse shaping and microfabrication
• Grantee: Cleber Renato Mendonça
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 11/06489-6 - EFFECT OF THE ULTRASHORT PULSE POLARIZATION ON THE TWO-PHOTON ABSORPTION OF ORGANIC COMPOUNDS
• Grantee: Marcelo Gonçalves Vivas
• Support Opportunities: Scholarships in Brazil - Post-Doctoral