Linear Photophysics, Stimulated Emission, and Ultrafast Spectroscopy of New Two-Photon Absorbing Diketopyrrolopyrrole Derivatives

Abstract

The synthesis and comprehensive linear photophysical and nonlinear optical characterization of new diketopyrrolopyrrole derivatives, 2-(2-ethylhexyl)-3,6-di(pyridin-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (1) and 2-(10-azidodecyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (2), are reported. The nature of the main linear absorption bands of 1 and 2 was ascertained based on experimental excitation anisotropy spectra and quantum chemical calculations. Three-dimensional fluorescence maps, emission lifetimes, and photochemical decomposition quantum yields of the new derivatives were obtained in a number of organic solvents at room temperature. Two-photon absorption (2PA) spectra of 1 and 2 were measured over a broad spectral range using an open aperture Z-scan technique, revealing a maximum 2PA cross section of ∼100 GM. Transient absorption and stimulated emission pump–probe measurements with femtosecond time resolution revealed two different types of fast relaxations in the excited states of 1 and 2, and one-photon stimulated emission depletion (STED) spectra were determined. Efficient superfluorescence emission of 1 was observed under femtosecond transverse pumping conditions. A quantum-mechanical investigation of the electronic structure of the new compounds was performed using TD-DFT methodology. Simulated linear absorption spectra, including Franck–Condon band structure of the first excited states, were found in good agreement with experimental data, while 2PA cross sections obtained without vibronic contributions were considerably underestimated.