Solvatochromic effects on a class of indoline derivatives organic photosensitizers: About the influence of hydrogen-bond acceptor and donor abilities parameters

Nowadays, new organic photosensitizers are replacing the commonly used Ru-complexes in dyes sensitized solar cells. Even when they are linked to TiO2 or ZnO2 semiconductors, their spectroscopic behavior can be influenced once immersed in a solvent. Therefore it is crucial to understand how solvatochromic effects can influence the photophysical properties of the organic photosensitizer and to isolate which solvent parameters can be responsible for the dye absorption spectral shifts. Here indoline derivative photosensitizers D205, D149 and D102 have been studied by steady-state spectroscopy. Some qualitative trends on the spectral shifts of those compounds have been first isolated. Then multilinear regression analyses following both Mamlet-Taft and Catalan scales have been applied to the observed spectral shifts (absorption maxima, emission maxima and Stokes shifts). Solvents dipolarity and polarizability are definitely the preponderant parameters which rule the spectroscopic characteristics of this class of dyes, but some interesting link has been evidenced between H-bond acceptor ability solvents parameter and a blue shift of absorption spectra of the dyes. This could lead to an alteration of the overlap of the photosensitizer absorption spectrum and the solar light, leading to a decrease of the photoconversion efficiency of the solar cell. Our results point out to the importance of the choice of the electrolyte, particularly their H-bond acceptor ability parameter, on the properties of the photosensitizer. (C) 2017 Elsevier B.V. All rights reserved.