Two-photon absorption and stimulated emission spectroscopy of squaraine derivative

Abstract

The nature of spontaneous and stimulated optical transitions of 2,4-Bis[4-(N,N-diphenylamino)-2,6-dihydroxyphenyl]squaraine (1) was analyzed based on comprehensive linear photophysical and nonlinear optical investigations in liquid solutions at room temperature, including excitation anisotropy, two-photon absorption (2 PA) spectra, and fast vibronic relaxation processes. The values of corresponding transition cross-sections of 1 were measured using a single-beam low-frequency loss modulation technique and fluorescence quenching method. Substantial differences between the absorption cross-sections maxima and corresponding stimulated emission ones were observed for 1 up to 7 times for one-photon optical transitions. 2 PA spectrum of 1 was obtained in a broad spectral range and maximum value of cross-section ∼3000 GM was shown. The relatively large 2 PA cross-sections and high efficiency of other stimulated optical transitions revealed high potential of 1 for a variety of nonlinear optical applications, including stimulated emission depletion (STED) microscopy.