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Spectroscopic Characterization and Modeling of Quadrupolar Charge-Transfer Dyes with Bulky Substituents

Sissa, Cristina and Terenziani, Francesca and Painelli, Anna and Siram, Raja Bhaskar Kanth and Patil, Satish (2012) Spectroscopic Characterization and Modeling of Quadrupolar Charge-Transfer Dyes with Bulky Substituents. In: Journal of Physical Chemistry B, 116 (16). pp. 4959-4966.

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Abstract

Joint experimental and theoretical work is presented on two quadrupolar D-pi-A-pi-D chromophores characterized by the same bulky donor (D) group and two different central cores. The first chromophore, a newly synthesized species with a malononitrile-based acceptor (A) group, has a V-shaped structure that makes its absorption spectrum very broad, covering most of the visible region. The second chromophore has a squaraine-based core and therefore a linear structure, as also evinced from its absorption spectra. Both chromophores show an anomalous red shift of the absorption band upon increasing solvent polarity, a feature that is ascribed to the large, bulky structure of the moleCules. For these molecules, the basic description of polar solvation in terms of a uniform reaction field fails. Indeed, a simple extension of the model to account for two independent reaction fields associated with the two molecular arms quantitatively reproduces the observed linear absorption and fluorescence as well as fluorescence anisotropy spectra, fully rationalizing their nontrivial dependence on solvent polarity. The model derived from the analysis of linear spectra is adopted to predict nonlinear spectra and specifically hyper-Rayleigh scattering and two-photon absorption spectra. In polar solvents, the V-shaped chromophore is predicted to have a large HRS response in a wide spectral region (approximately 600-1300 nm). Anomalously large and largely solvent-dependent HRS responses for the linear chromophores are ascribed to symmetry lowering induced by polar solvation and amplified in this bulky system by the presence of two reaction fields.

Item Type: Journal Article
Additional Information: Copyright of this article is belongs to American Chemical Society.
Keywords: NONLINEAR-OPTICAL PROPERTIES; HETEROJUNCTION SOLAR-CELLS; 2-PHOTON ABSORPTION; SQUARAINE DYES; PHOTOPHYSICAL PROPERTIES;1ST HYPERPOLARIZABILITY;SYMMETRY-BREAKING; NANOCRYSTALLINE TIO2;CONJUGATED MOLECULES;SOLVENT POLARITY
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited: 22 Aug 2012 04:38
Last Modified: 22 Aug 2012 04:38
URI: http://eprints.iisc.ernet.in/id/eprint/44447

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