chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, solvatochromism is the phenomenon observed when the

colour Color (or colour in Commonwealth English; see spelling differences) is the visual perception based on the electromagnetic spectrum. Though color is not an inherent property of matter, color perception is related to an object's light absorp ...

of a

solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Solu ...

is different when the solute is dissolved in different

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

The solvatochromic effect is the way the spectrum of a substance (the solute) varies when the substance is dissolved in a variety of solvents. In this context, the

dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insul ...

and

hydrogen bonding In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

capacity are the most important properties of the solvent. With various solvents there is a different effect on the electronic

ground state The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state ...

and

excited state In quantum mechanics Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Add ...

of the solute, so that the size of energy gap between them changes as the solvent changes. This is reflected in the

absorption Absorption may refer to: Chemistry and biology *Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which su ...

emission spectrum The emission spectrum of a chemical element or chemical compound is the Spectrum (physical sciences), spectrum of frequencies of electromagnetic radiation emitted due to electrons making a atomic electron transition, transition from a high energ ...

of the solute as differences in the position, intensity, and shape of the spectroscopic bands. When the spectroscopic band occurs in the visible part of the

electromagnetic spectrum The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...

, solvatochromism is observed as a change of

. This is illustrated by Reichardt's dye, as shown in the image. Negative solvatochromism corresponds to a hypsochromic shift (or blue shift) with increasing solvent polarity. An examples of negative solvatochromism is provided by
4-(4-hydroxystyryl)-''N''-methylpyridinium iodide, which is red in 1-propanol, orange in

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

, and yellow in

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

. Positive solvatochromism corresponds to a bathochromic shift (or red shift) with increasing solvent polarity. An example of positive solvatochromism is provided by 4,4'-bis(dimethylamino)fuchsone, which is orange in

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...

, red in

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

. The main value of the concept of solvatochromism is the context it provides to predict colors of solutions. Solvatochromism can in principle be used in

sensor A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...

s and in

molecular electronics Molecular electronics is the study and application of molecular building blocks for the fabrication of electronic components. It is an interdisciplinary area that spans physics, chemistry, and materials science. It provides a potential means to ...

for construction of molecular switches. Solvatochromic dyes are used to measure solvent parameters, which can be used to explain solubility phenomena and predict suitable solvents for particular uses. Solvatochromism of the

photoluminescence Photoluminescence (abbreviated as PL) is light emission from any form of matter after the absorption of photons (electromagnetic radiation). It is one of many forms of luminescence (light emission) and is initiated by photoexcitation (i.e. phot ...

fluorescence Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...

carbon nanotubes A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized: * ''Single-walled carbon nanotubes'' (''SWC ...

has been identified and used for optical sensor applications. In one such application, the

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

of the fluorescence of peptide-coated carbon nanotubes was found to change when exposed to

explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ex ...

s, facilitating detection. However, more recently the small chromophore solvatochromism hypothesis has been challenged for carbon nanotubes in light of older and newer data showing electrochromic behavior. These and other observations regarding non-linear processes on the semiconducting nanotube suggest colloidal models will require new interpretations that are in line with classic semiconductor optical processes, including electrochemical processes, rather than small molecule physical descriptions. Conflicting hypotheses may be due to the fact the nanotube is only a single atom thick material interface unlike other "bulk" nanomaterials.

References

External links

Negative solvatochromism experiment

{{Authority control Chromism Absorption spectroscopy

References

Further reading

External links