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Why do fluorescent dyes emit a different color of light than they absorb?

An excited fluorophore molecule emits lower-energy light than the light it absorbs. This range of wavelengths reflects the range of possible excited states that the fluorophore can achieve. So for each fluorescent dye, there is a specific wavelength—the excitation maximum—that most effectively induces fluorescence.

Why is it called the Stokes Shift? This is Stokes’ Law and states that the fluorescence emission occurs at a longer wavelength than the incident light. The shift to longer wavelength between the absorption and fluorescence spectra is accordingly called the Stokes shift in his honour.

What would be the difference between an excitation and emission spectrum in fluorescence spectroscopy?

The excitation spectrum shows at what wavelengths the solution uses to produce its fluorescence. The emission spectrum shows what wavelengths are given off from the solution. The excitation spectrum has the same peaks as the absorbency spectrum; although the absorbency spectrum may have more peaks.

What is red shift in fluorescence?

Red-shifted vs. – A spectral shift towards higher wavelengths (i.e. lower energy and lower frequency) is called a red-shift or a bathochromic shift. – A spectral shift towards lower wavelengths (i.e. higher energy and higher frequency) is called a blue-shift or hypsochromic shift.

What is bathochromic shift with example?

A covalently unsaturated group responsible for electronic absortion (for example, C=C, C=O, and NO2). BATHOCHROMIC SHIFT. The shift of absorption to a longer wavelength due to substitution or solvent effect (a red shift).

Which of the following will show more bathochromic shift?

All these are aromatic compounds and undergo pi to pi transition. Therefore the group that has n electrons and facilitates the pi to pi transition will have more bathochromic shift. Here the phenoxide ion has more number of lone pair of electrons, hence shows greater bathochromic shift.

What is the cause of bathochromic shift?

Hypochromic effect Bathochromic shift/effect (Red shift): It is an effect due to which the absorption maximum is shifted towards longer wavelength for the presence of an auxochrome or by the change of polarity of solvent. In addition, the presence of alkyl group on the double bond causes bathochromic shift.

Why does P nitrophenol show red shift in alkaline medium?

Red color is present in the visible spectrum and has a longer wavelength compared to other colors, this phenomenon is called the red shift. In an alkaline medium, p-nitrophenol shows red shift since the negatively charged oxygen molecules delocalise effectively compared to the unshared electron pair.

What is Hypochromic and Hyperchromic shift?

Terminology for absorption shifts Hypsochromic: a shift of a band to higher energy or shorter wavelength (often called a blue shift). Hyperchromic: an increase in the molar absorptivity. Hypochromic: an decrease in the molar absorptivity.

What does red shift mean?

‘Red shift’ is a key concept for astronomers. The term can be understood literally – the wavelength of the light is stretched, so the light is seen as ‘shifted’ towards the red part of the spectrum. Something similar happens to sound waves when a source of sound moves relative to an observer.

What is the difference between Bathochromic compound and Hypsochromic compound?

Bathochromic shift: In spectroscopy, the position shift of a peak or signal to longer wavelength (lower energy). A hypsochromic shift is the shift of a peak or signal to shorter wavelength (higher energy).

What does the notation σ * ← n mean?

What does the notation σ*←n mean? Emission; transition from a quantum level n to σ* MO. Absorption; transition from a non-bonding MO to σ* MO. Absorption; transition from a quantum level n to σ* MO.

What is blue shift in chemistry?

A blueshift is any decrease in wavelength (increase in energy), with a corresponding increase in frequency, of an electromagnetic wave; the opposite effect is referred to as redshift. In visible light, this shifts the color from the red end of the spectrum to the blue end.

How does Auxochrome affect the chromophores position?

However, if an auxochrome is present in the meta position to the chromophore, it does not affect the color. An auxochrome is known as a compound that produces a bathochromic shift, also known as red shift because it increases the wavelength of absorption, therefore moving closer to infrared light.

Which one is not the example of Auxochrome?

>C=N is not an auxochrome.

Which statement is true for Auxochrome?

2. Which statement is true about Auxochrome ? A. It is only saturated compound.

Which group is not an example of chromophores?

A compound containing only a chromophore may be coloured material but not a dye. For example azo benzene is red coloured but not a dye. Where as para amino azobenzene (aniline yellow) is a dye. Step by step solution by experts to help you in doubt clearance & scoring excellent marks in exams.

Are chromophores positively or negatively charged?

Chromophores: Groups with conjugated double bonds that give the dye its color. Direct, cationic, basic or positive dyes: contain positively charged groups. Examples include methylene blue, basic fuchsin, and crystal violet. These dyes directly bind to and stain the negatively charged surface of bacterial cells.

What is the difference between chromophore and Auxochrome?

Chromophore is that part of the molecule which when exposed to visible light will absorb and reflect a certain color. Auxochrome is a group of atoms which is functional and has the capability to alter the capacity of the chromophore to reflect colors. Auxochrome increases the color of any organic substance.

Which of the following is chromophore formula?

Chromophore is part of molecule responsible for its colour. For azo dyes , the general formula is R−N=N−R′ and the chromophore is the azo group( -N=N- ).

Is benzene a chromophore?

The Benzene Ring as an Optically Active Chromophore.

When absorption intensity of compound is decreased it is called?

Hypochromic shift :- when absorption intensity of compound is decreased it is called hypochromic shift.