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Issue 1, 2020
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About the origin of the large Stokes shift in aminoalkyl substituted heptamethine cyanine dyes

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Abstract

Aminoalkyl-substituted heptamethine cyanine dyes are characterized by a large Stokes shift, an uncommon feature for cyanine molecules yet very promising for their application as fluorescent probes in bioimaging and as light harvesting antennas in biohybrid systems for solar energy conversion. The origin of this photophysical feature has not been adequately explored so far, and a combined experimental and theoretical work is herein provided to shed light on the role played by the central aminoalkyl substituent bound to the heptamethine cyanine backbone in defining the unusual properties of the dye. The spectra recorded in solvents of different polarities point to a marginal role of the medium in the definition of the Stokes shift, which conversely can be ascribed to the relaxation of the molecular geometry upon photoexcitation. This hypothesis is supported by an extensive theoretical investigation of the ground and excited states of the dye. TD-DFT results on the aminoalkyl-substituted dye and its unsubstituted precursor demonstrate a very similar cyanine-like structure for both molecules in the relaxed excited state. Conversely, in the ground state the amino substitution disrupts the conjugation in the polymethine chain, leading to a broken-symmetry, non-planar structure.

Graphical abstract: About the origin of the large Stokes shift in aminoalkyl substituted heptamethine cyanine dyes

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Supplementary files

Article information


Submitted
07 Oct 2019
Accepted
01 Nov 2019
First published
10 Dec 2019

This article is Open Access

Phys. Chem. Chem. Phys., 2020,22, 129-135
Article type
Paper

About the origin of the large Stokes shift in aminoalkyl substituted heptamethine cyanine dyes

C. Sissa, A. Painelli, F. Terenziani, M. Trotta and R. Ragni, Phys. Chem. Chem. Phys., 2020, 22, 129
DOI: 10.1039/C9CP05473A

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