Question

During the deepening of the colour of a dye, the absorption shifts towards red. This shifting is called (a) bathochromic shift (b) hypochromic shift (c) hyperchromic shift (d) auxochromic shift

Short answer

The correct answer is (a) bathochromic shift.

Step-by-step solution

Understanding the Terms

First, let's break down the terms in the choices provided. A 'bathochromic shift' refers to a change in absorption of light towards longer wavelengths (which means shifting towards the red end of the spectrum). A 'hypochromic shift' involves a decrease in absorbance intensity. A 'hyperchromic shift' describes an increase in absorbance intensity. An 'auxochromic shift' involves modifications in absorbance intensity due to auxiliary groups attached to a chromophore.

Assessing the Options

Next, analyze the specific scenario described in the problem: 'the absorption shifts towards red'. Bathochromic shifts are known for causing absorption to move towards longer wavelengths, which corresponds to the red end of the spectrum. The other types of shifts mentioned do not relate to changes in the position of absorption in terms of wavelength.

Identifying the Correct Answer

Based on the definitions analyzed, the correct type of shift describing a move of absorption towards red is the 'bathochromic shift'. Therefore, the absorption shift described in the question is a bathochromic shift.

Key concepts

Chromophore

Chromophores are molecules or parts of molecules that are responsible for the color of compounds. They absorb certain wavelengths of light, while reflecting or transmitting others, giving rise to visible color. The core part of a chromophore is often a conjugated system, consisting of alternating single and double bonds, which allows them to interact with light at particular wavelengths.
When light hits a chromophore, it absorbs energy and causes transitions in the electronic state of the molecule. This absorption determines the specific color seen.

• The energy level difference between the ground state and the excited state dictates which wavelength of light is absorbed.
• Chromophores are essential components in dyes, pigments, and even some proteins and biochemicals.

Understanding how chromophores work is fundamental to predicting how a substance interacts with light and what colors might be observed. For instance, in chemical reactions, if the structure of a chromophore is altered, the color, which is observed, can significantly change.
So whenever there's a shift in color due to a chemical reaction or interaction, it’s likely because the chromophore’s characteristics have been modified.

Absorption Shifts

Absorption shifts refer to changes in the wavelengths at which a substance absorbs light. These shifts are indicators of alterations in the electronic environments of molecules or molecular systems. Often, they signal changes in structure or interactions with the environment, such as changes in solvents or bonding scenarios.
One type of absorption shift is the bathochromic shift, also called a red shift, where the absorption moves to longer wavelengths, such as what occurs when moving towards the red part of the light spectrum.

• Bathochromic shifts are often indicative of increased conjugation in the molecule or due to electron-donating groups.
• Conversely, a hypsochromic shift, or blue shift, refers to absorption shifting to shorter wavelengths.

Understanding these shifts can offer insights into the molecular structure and environment. For instance, in research and chemical analysis, observing absorption shifts can help chemists infer structural details of unknown compounds or ascertain changes during a chemical reaction.
Analyzing absorption shifts is a key technique in various scientific disciplines, including chemistry, physics, and biology.

Wavelength

Wavelength is a measure of distance over which a wave's shape repeats. Generally, it refers to the distance between consecutive crests or troughs in a wave. Wavelengths are crucial in defining the energy and color of light.
In the context of light, shorter wavelengths correspond to higher energy and blue/violet colors, while longer wavelengths are linked to lower energy and red/orange colors.

• Visible light, which is only a small portion of the electromagnetic spectrum, encompasses wavelengths from about 400 nm to 700 nm.
• A change in the color of a substance, such as a dye, can be due to a bathochromic shift, where absorption changes from shorter to longer wavelengths.

Understanding wavelength and its role is essential for interpreting how different substances interact with light. It allows us to predict what color will manifest if a particular wavelength is absorbed, making it a fundamental concept in the study of light and color perception.
By understanding wavelength, you can better grasp how substances like dyes change color under different circumstances, which relates directly to the absorption shifts and the nature of chromophores discussed earlier.