Question: Why Do Some Absorbing Compounds Fluoresce But Others Do Not?

Why do some compounds fluoresce?

Generally molecules that fluoresce are conjugated systems.

Fluorescence occurs when an atom or molecules relaxes through vibrational relaxation to its ground state after being electrically excited.

The specific frequencies of excitation and emission are dependent on the molecule or atom..

Does pH affect fluorescence?

Increasing the pH caused a corresponding increase in the maximum fluorescence intensity from 77.74 (units) in the acidic sample to 146.13 at neutral pH and 232.69 at alkaline pH.

Why is Spectrofluorometry potentially more sensitive than spectrophotometry?

The basic principle is that each compound absorbs or transmitslight over a certain range of wavelength. Now why is spectrofluorometry potentially more sensitive than spectrophotometry because For spectrofluorometry, the analytical signal F is proportional to the source intensity P0 and the transducer sensitivity.

What causes phosphorescence?

Fluorescence, emission of electromagnetic radiation, usually visible light, caused by excitation of atoms in a material, which then reemit almost immediately (within about 10−8 seconds). The initial excitation is usually caused by absorption of energy from incident radiation or particles, such as X-rays or electrons.

Why do minerals fluoresce?

Many minerals fluoresce when viewed with ultraviolet light due to the presence of trace minerals called activators. The unique ability of activators is due to their electrons being spaced at just the right distance from the nucleus to absorb UV light and emit it in visible wavelengths.

Is fluorescence or absorbance more sensitive?

Fluorescence is more sensitive because of the different ways of measuring absorbance and fluorescence. Light absorbance is measured as the difference in intensity between light passing through the reference and the sample. In fluorescence the intensity is measured directly, without comparison with a reference beam.

What types of molecules fluoresce?

A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds.

Is fluorescence proportional to concentration?

Fluorescence spectroscopy can be used to measure the concentration of a compound because the fluorescence intensity is linearly proportional to the concentration of the fluorescent molecule.

What does excitation wavelength mean?

Excitation spectra. A fluorophore is excited most efficiently by light of a particular wavelength. This wavelength is the excitation maximum for the fluorophore. Light with a wavelength near the excitation maximum can also cause excitation, as shown by the shaded areas below, but it does so less efficiently.

What is excitation and emission wavelength?

The wavelength of excitation monochromator is set to a wavelength of known absorption by the sample, and the wavelength of the emission monochromator is scanned across the desired emission range and the intensity of the fluorescence recorded on the detector as a function of emission wavelength.

Why do some compounds fluoresce in ultraviolet light?

Fluorescence occurs when a substance releases absorbed energy in the form of light. A fluorescent substance absorbs electromagnetic radiation (often ultraviolet light), which promotes the electrons to a higher energy level. While in the higher energy state, the electron loses some energy in the form of heat.

What is the difference between absorption and fluorescence spectroscopies?

One major difference between the two methods is the light detector in absorbance spectroscopy is in line with the light path and the sample, whereas in fluorescence spectroscopy the light source and detector are at 90o to each other, with respect to the sample.

Why does pH affect fluorescence?

pH affects the fluorescence of abiotic preparations of porphyrins caused by changes in speciation between monomers, higher aggregates and dimers, but this phenomenon has not been demonstrated in bacteria. Fluorescence spectra were obtained from suspensions of P.

What is the relationship between excitation and emission wavelengths?

As a result, the emission spectrum is shifted to longer wavelengths than the excitation spectrum (wavelength varies inversely to radiation energy). This phenomenon is known as Stokes Law or Stokes shift. The greater the Stokes shift, the easier it is to separate excitation light from emission light.

Do all molecules fluoresce?

Generally molecules that fluoresce are conjugated systems. Fluorescence occurs when an atom or molecules relaxes through vibrational relaxation to its ground state after being electrically excited. The specific frequencies of excitation and emission are dependent on the molecule or atom.

Why do some molecules fluoresce and others don t?

Why do some objects fluoresce and others don’t? -It is all in the structure of the objects molecules and if the electrons are able to absorb photons and move around between different molecules to release a new photon of energy. In this image we can see a visual representation of what happens when a photon gets excited.

Why is emission wavelength longer than excitation?

When electrons go from the excited state to the ground state (see the section below entitled Molecular Explanation), there is a loss of vibrational energy. As a result, the emission spectrum is shifted to longer wavelengths than the excitation spectrum (wavelength varies inversely to radiation energy).

Why is fluorescent better than absorbance?

Sensitivity: The sensitivity of fluorescence detection is approximately 1,000 times greater than absorption spectrophotometric methods. This leads to greater limits of detection, while potentially using less sample material. This is important especially when working with precious or limited-quantity materials.

Is GFP a fluorophore?

The Chromophore of GFP. GFP is unique among fluorescent proteins in that its fluorophore is not a seperately synthesized prostethic group but composed of modified amino acid residues within the polypeptide chain.

What type of Fluorochromes exist?

The most commonly used fluorophore is Fluorescein IsoThioCyanate (FITC). Today’s large selection of fluorophores consists of three groups: synthetic organic dyes (such as FITC), biological fluorophores such as the Green Fluorescent Protein (GFP), discussed below and Quantum Dots (QD) (see Chapter 4).