Color in Bridge-Substituted Cyanines

Abstract

Theories of color in cyanine dyes have evolved around the idea of a "resonance" of structures with distinct bonding and charge localization. Understanding the emergence of resonance models from the underlying many-electron problem remains a central issue for these systems. Here, the issue is addressed using a maximum-entropy approach to valence-bond representations of state-averaged complete-active space self-consistent field models. The approach allows calculation of energies and couplings of high-energy valence-bond structures that mediate superexchange couplings and chemical bonding. A series of valence-bond Hamiltonians for a series of bridge-substituted derivatives of Michler's hydrol blue (a monomethine cyanine) is presented. The Hamiltonians are approximated with a simple linear model parametrized by the Brown-Okamoto σ parameter of the bridge substituent. A quantitative lower bound on σ, beyond which a resonant cyanine-like ground state will not exist, is presented. The large effective coupling in two-state resonance models emerges from superexchange associated with either covalent bonding or charge-carrier delocalization, with the former contribution significantly the stronger. The results provide ab initio justification for empirical diabatic-state models of methine optical response. They are of general interest for understanding the optoelectronic response in cyanines.

Unified Model for Photophysical and Electro-Optical Properties of Green Fluorescent Proteins

“…Historically, the use of resonance theory to understand dye colors can be traced back to Platt’s quantum mechanical explanation of Brooker’s empirical rules for cyanine dyes. , The driving force was formulated under the name “difference basicity” and shown to be transferrable and additive among dyes with different combinations of moieties. Ongoing interest in nonlinear optical properties ,, resulted in the resurrection of this valence-bond approach as opposed to the more widely practiced molecular orbital theory, culminating in a series of Olsen and McKenzie papers demonstrating that an effective two-state model indeed captures the essential physics of the cyanine dyes, confirmed by high-level computational methods. − This was later applied to numerous dyes, − particularly the GFP chromophore ,,,, (see also ref ). Note that this formalism is equivalent to Marcus–Hush theory without nuclear degrees of freedom considered, and thus properties related to nuclear rearrangement, such as Stokes shift and vibronic structure, cannot be accounted for.…”

The Chromogen, Structure, Inspirations, and Applications of a Photo-, pH-, thermal-, Solvent-, and Mechanical-Response Epoxy Resin

“…When one of three benzene rings is removed, the rest (diarylmethane 34 ) shares a similar structure in common with MC-1. Search results show that the structure in Figure 8 is a known substanceMichler's hydrol blue, 35,36 which shares the same color with the solution of MC-1. Michler's hydrol blue is one kind of artificial colors (diarylmethane dye).…”

Preparation and Properties of a Self-Healing, Multiresponsive Color-Change Hydrogel

“…The application of the hydrogel system is also worth noting. The whole preparation process was both efficient and simple. , …”

“…When the MHB was dissolved in CCl 4 , the solution became transparent and colorless (see Figure 1a, MHB/CCl 4 ). When the solution was irradiated under UV light for about 60 s, the color changed to blue (see Figure 1a, PMHB/CCl 4 ), because the MHB structure changed to that of PMHB (see Figure 1b), 34 and its solubility also changed from hydrophobic to hydrophilic. 29 At this time, the HA gel was immediately immersed into the blue solution of PMHB/CCl 4 (see Figure 1a, HA gel/PMHB/CCl 4 ).…”

“…The whole preparation process was both efficient and simple. 29,34 3.2. Multiresponsive Performance.…”