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Solvatochromic shift mechanisms of centrosymmetric chromophores in polar liquids

Paper ID Volume ID Publish Year Pages File Format Full-Text
27124 44003 2012 10 PDF Available
Title
Solvatochromic shift mechanisms of centrosymmetric chromophores in polar liquids
Abstract

Origins of absorption shifts in polar liquids are considered for centrosymmetric chromophores devoid of dipole moments. The refractive index (n) dependent bathochromism shows that the excited state is always more polarizable than ground state. With increasing solvent dielectric constant (ɛ), mainly red shifts occur, but there are exceptions. Hypsochromism of n–π* transition in s-tetrazine is ascribed to a decrease of quadrupole moment in the excited state. In this case the upper level is pushed up in the reaction field of the ground-state quadrupole. Red shifts of intense bands in polyenes (11Bu or S2) and polyarenes (1Bb or β), reaching ∼−250 cm−1 are assigned to local polarization in the reaction fields of chromophore bond dipoles. The hyperbolic-like ɛ-dependence of solvent shift, approximated to an empirical function (ɛ − n2)/(ɛ − n2 + c), is much steeper (with “stretching” factor c = 3 ± 0.5) in this case, as compared to that for the linear effect (for s-tetrazine, c = 9). Polarization mechanism also causes less band broadening in polar environments. Contrary to a common view, the spectral shift is probing local reaction fields of chromophores, rather than random fields in the cavities accommodating the dye. Negligible polarization in solvent “cavity” fields is in accordance with earlier hole-burning study of matrix induced dipole moments in tetrapyrrolic pigments that depend surprisingly little on the polarity of polymeric hosts (R.B. Altmann, I. Renge, L. Kador, D. Haarer, J. Chem. Phys. 97 (1992) 5316 [30]).

► Absorption is a sensitive probe to intermolecular interactions. ► Solvent polarity causes spectral shift in apolar dyes. ► Most shifts are bathochromic, but blue shifts can occur. ► Centrosymmetric chromophore creates multipolar reaction field. ► Linear and quadratic Stark effects are distinguished.

Keywords
Absorption spectrum; Dielectric theory; Quadratic Stark effect; Polyene; Random field; Solvent shift
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 239, 1 July 2012, Pages 7–16
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us