Title

Two-Photon Absorption Spectra Of A Near-Infrared 2-Azaazulene Polymethine Dye: Solvation And Ground-State Symmetry Breaking

Abstract

Polymethine dyes (PDs) with absorption bands in the near-infrared region undergo symmetry breaking in polar solvents. To investigate how symmetry breaking affects nonlinear optical responses of PDs, an extensive and challenging experimental characterization of a cationic 2-azaazulene polymethine dye, including linear absorption, fluorescence, two-photon absorption and excited-state absorption, has been performed in two solvents with different polarity. Based on this extensive set of experimental data, a three-electronic-state model, accounting for the coupling of electronic degrees of freedom to molecular vibrations and polar solvation, has been reliably parameterized and validated for this dye, fully rationalizing optical spectra in terms of spectral position, intensities and bandshapes. In low-polarity solvents where the dye is mainly in its symmetric form, a nominally forbidden two-photon absorption band is observed, due to a vibronic activation mechanism. Inhomogeneous broadening plays a major role in polar solvents: absorption spectra represent the weighted sum of contributions from states with a variable amount of symmetry breaking, leading to a complex evolution of linear and nonlinear optical spectra with solvent polarity. In more polar solvents, the dominant role of the asymmetric form leads to the activation of two-photon absorption as a result of the symmetry lowering. The subtle interplay between the two mechanisms for two-photon absorption activation, vibronic coupling and polar solvation, can be fully accounted for within the proposed microscopic model allowing a detailed interpretation of the optical spectra of PDs. © the Owner Societies 2013.

Publication Date

5-28-2013

Publication Title

Physical Chemistry Chemical Physics

Volume

15

Issue

20

Number of Pages

7666-7678

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1039/c3cp50811k

Socpus ID

84877260845 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/84877260845

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