Substituent Effects on the Solubility and Electronic Properties of the Cyanine Dye Cy5: Density Functional and Time-Dependent Density Functional Theory Calculations.

Austin Biaggne,William B Knowlton,Bernard Yurke,Jeunghoon Lee,Lan Li

doi:10.3390/molecules26030524

Abstract

The aggregation ability and exciton dynamics of dyes are largely affected by properties of the dye monomers. To facilitate aggregation and improve excitonic function, dyes can be engineered with substituents to exhibit optimal key properties, such as hydrophobicity, static dipole moment differences, and transition dipole moments. To determine how electron donating (D) and electron withdrawing (W) substituents impact the solvation, static dipole moments, and transition dipole moments of the pentamethine indocyanine dye Cy5, density functional theory (DFT) and time-dependent (TD-) DFT calculations were performed. The inclusion of substituents had large effects on the solvation energy of Cy5, with pairs of withdrawing substituents (W-W pairs) exhibiting the most negative solvation energies, suggesting dyes with W-W pairs are more soluble than others. With respect to pristine Cy5, the transition dipole moment was relatively unaffected upon substitution while numerous W-W pairs and pairs of donating and withdrawing substituents (D-W pairs) enhanced the static dipole difference. The increase in static dipole difference was correlated with an increase in the magnitude of the sum of the Hammett constants of the substituents on the dye. The results of this study provide insight into how specific substituents affect Cy5 monomers and which pairs can be used to engineer dyes with desired properties.

Highlights

This paper demonstrates that the hydrophobicity and ∆d of a Cy5 dye can be altered without degrading μ
Please note that our study focuses on the computational screening of potential Cy5 substituents that could increase the ∆d value of pristine Cy5 but not decrease its μ value
We performed density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations to determine the effects various substituents had on the ∆Gsolv, μ, and ∆d of Cy5

Summary

Introduction

Dyes in natural [1,2,3] and synthetic [4,5,6,7,8] systems have been shown to exhibit molecular aggregation behavior of which exciton delocalization is a signature. Exciton delocalization can be described as the collective sharing of an electronic excitation over dyes within an aggregate due to the transition dipole-dipole coupling between the dyes. The dyes can assume various stacking geometries that can be best described in the context of the simplest dye aggregate—the dimer. Potential applications of excitonic properties of dye aggregates include organic photovoltaics [16], non-linear optics [17], and quantum computing [18,19]. The functionality of excitonic devices utilizing dye aggregate properties

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