Which of the following best explains the differences in the absorption wave, the

Question

Which of the following best explains the differences in the absorption wave, the molecules labeled "HPSensor 1", HPSensor 2", and "HPSensor 3"? rth observed between ethanol, water, and CH2 C12 for For all three dyes, the molecules have a higher wavelength in CH2 Cl2 indicating a lower difference in energy between the HOMO and LUMO compared to water and ethanol. Ethanol and water have hydrogen bonding donors and acceptors that can interact with hydrogen bond donors and acceptors on the dyes. Hydrogen bonding between the solvent and the dye molecule could stabilize the HOMO (ground state) of the molecule, which would result in a larger difference in energy and a shorter wavelength compared to a solvent that did not have hydrogen bonding capabilities like CH2 Cl2 The different solvents clearly impact the absorption wavelength experimentally observed. However, the trends are different for each dye such that a hypothesis can not be formed about how solvent impacts the color of the molecule. O B For all three dyes, the molecules have a higher wavelength in CH2 Cl2 indicating a lower difference in energy between the HOMO and LUMO compared to water and ethanol. Ethanol and water have hydrogen bonding donors and acceptors that can interact with hydrogen bond donors and acceptors on the dyes. Hydrogen bonding between the solvent and the dye molecule could destabilize the HOMO (ground state) of the molecule, which would result in a larger difference in energy and a higher wavelength compared to a solvent that did not have hydrogen bonding capabilitislike CH C Although the differences on solvent are minor, there are clear trends. For all three dyes, water results in the lowest wavelength, ethanol results the intermediate wavelength, and CH2 Cl2 results in the highest wavelength. CH2 Cl stabilizes the molecules through very strong London Dispersion forces, reducing the electronic transition and increases the wavelength. O D Although the differences on solvent are minor, there are clear trends.For all three dyes, ethanol results in the lowest wavelength, water results the intermediate wavelength, and CH2 Cl2 results in the highest wavelength CH2 Cl2 stabilizes the HOMO (ground state) and LUMO (to a lesser extent than the HOMO) through very strong ion dipole forces, reducing the energy difference between the HOMO and LUMO and, thus, increases the wavelength.

Explanation / Answer

The correct option is A

Here the dyes are acting as a hydrophobic sensors, water is most hydrophilic / least hydrophobic (with 2 hydrogen bond donors) which stabilizes the HOMO of the dye, and hence larger energy gap between HOMO (ground state) and LUMO, so require more energy for the electronic transition and it occurs at lower wavelength. Among 3 dyes, in all cases, water has the least abortion wavelength. Ethanol is medium hydrophobic with 1 hydrogen bond donor, in all cases, its absorption peak appears between water and CH2Cl2. Finally, CH2Cl2 is most hydrophobic (with no H-bond donors), so the stabilization effect on HOMO is lost and energy gap between HOMO and LUMO get reduced and absorb at a higher wavelength.

The option B is wrong because hypotheses can be made and can be related to the hydrophobic effect of the solvents.

The option C is wrong because, Destabilizing HOMO reduces the energy gap between HOMO and LUMO, hence at absorption should be at a larger wavelength.

The option D is wrong because the difference is due to hydrophobic effect not due to London dispersion.

The option E is wrong because not ethanol but water has the lowest absorption peak.

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