What is the Difference Between Fluorophore and Chromophore

The main difference between fluorophore and chromophore is that fluorophore is a part of a molecule, re-emitting the absorbed photon at a longer wavelength whereas chromophore is a part of a molecule, absorbing UV or visible light to emit light in the visible region. Therefore, a fluorophore can emit high energy while a chromophore emits lower energy. Furthermore, the two main types of fluorophores are extrinsic and intrinsic fluorophores while the two main types of chromophores are conjugated π bond system and metal complex chromophores.

Fluorophore and chromophore are two types of parts found in certain molecules responsible for their fluorescence or color respectively. Therefore, the molecules with those parts are used in different applications as indicators.

Key Areas Covered

1. What is a Fluorophore
     – Definition, Types, Importance
2. What is a Chromophore
     – Definition, Types, Importance
3. What are the Similarities Between Fluorophore and Chromophore
     – Outline of Common Features
4. What is the Difference Between Fluorophore and Chromophore
     – Comparison of Key Differences

Key Terms

Chromophore, Color, Emission, Excitation, Fluorophore, Fluorescence

What is a Fluorophore

A fluorophore is a functional group of a molecule responsible for emitting fluorescence by the molecule. The excitation wavelengths of a fluorophore range from UV to blue light. Significantly, fluorophore emits higher wavelengths. Here, the absorption of photons in the light puts the fluorophore into an excited electronic singlet state known as S₁. However, this excited state only lasts for a finite time, typically 1-10 ns. During the excited state, the fluorophore undergoes a conformational change, partially dissipating the energy of S₁ through vibrational relaxation. The emission of fluorescence brings the fluorophore to its group state known as S₀.  However, the energy of the emitting photons is low; hence the wavelength is longer. Also, the exciting and emitting wavelengths are overlapping in case of a fluorophore.

Figure 1: Fluorescence under  Microscope

The two main types of fluorophores are intrinsic fluorophores, which naturally occur in a sample, and extrinsic fluorophores, whihc are added to the sample in order to change the spectral properties of the sample.

What is a Chromophore

A chromophore is a part of a molecule responsible for its color. Here, the excitation wavelengths can be in the UV to the visible range. But, the emitting wavelengths occur in the visible range, giving a specific color to the molecule, which is visible to the naked eye. Chromophore undergoes a conformational change as occurs in the fluorophore and the returning to the ground state results in emission of the color.

Figure 2: Absorption of Carotenoids

Furthermore, the two types of chromophore systems are conjugated π bond system and metal complex chromophores. In the conjugated π bond system, electrons jump between energy levels, which are extended π orbitals. This type of chromophores includes food colorings, pH indicators, fabric dyes, carotenoids, etc. On the other hand, the metal complex chromophores consist of a metal in a coordination complex with a ligand. Some examples of this type of chromophores are chlorophylls, hemoglobin, etc.

Similarities Between Fluorophore and Chromophore

• Fluorophore and chromophore are two types of components present in certain molecules responsible for their fluorescent and color, respectively.
• Due to their ability to emit either fluorescent or color, they are used as reporter or indicator molecules in various applications.
• They can absorb light ranging from UV to the visible light.
• Also, both fluorophore and chromophore undergo a conformational change upon excitation and their return to the ground state emits either fluorescence or light.

Difference Between Fluorophore and Chromophore

Definition

Fluorophore refers to a fluorescent chemical compound that can re-emit light upon light excitation while chromophore refers to an atom or group whose presence is responsible for the color of a compound. Thus, this is the main difference between fluorophore and chromophore.

Excitation

Moreover, another difference between fluorophore and chromophore is that the fluorophores can absorb light ranging from UV to blue light while chromophores can absorb light ranging from UV to the visible region.

Emission

A fluorophore can emit light in higher wavelengths while chromophore can emit light in the visible range. Hence, this is one other difference between fluorophore and chromophore.

Overlapping Exciting and Emitting Wavelengths

Furthermore, an important difference between fluorophore and chromophore is that the exciting and emitting wavelengths are overlapping in a fluorophore while exciting and emitting wavelengths do not overlap in a chromophore.

Significance

Besides, a fluorophore is responsible for the fluorescence of a molecule while a chromophore is responsible for the color of a molecule.

Emission of Energy

Also, one more difference between fluorophore and chromophore is that fluorophore can emit high energy while a chromophore can emit low energy.

Temperature Dependency

Additionally, the emission of a fluorophore depends on the temperature while the emission of a chromophore does not depend on the temperature.

Types

The two main types of fluorophores are extrinsic and intrinsic fluorophores while the two main types of chromophores are conjugated π bond system and metal complex chromophores.

Conclusion

A fluorophore is a part of a molecule that can absorb light ranging from UV to blue light, emitting the light in higher wavelengths. In contrast, a chromophore is another part of molecules that can absorb light from UV to the visible range, emitting the light in the visible range. Therefore, a fluorophore emits fluorescence while a chromophore is responsible for the color of the molecule. However, the main difference between fluorophore and chromophore is the wavelengths emitted.

References:

1. “Fluorophores.” ScienceDirect, Elsevier B.V., Available Here.
2. “Chromophore.” ScienceDirect, Elsevier B.V., Available Here.

Image Courtesy:

1. “Bloodcell sun flares pathology” (Public Domain) via Commons Wikimedia  
2. “Carotenoids Absorption Spectrum” By byr7 (CC BY 2.0) via Flickr