P-chem experiment Absorption Spectra of Conjugated Dyes The polymethine dyes use
ID: 530167 • Letter: P
Question
P-chem experiment Absorption Spectra of Conjugated Dyes
The polymethine dyes used for this experiment are:
3,3’-diethylthiacyanine iodide Solution 1
3,3’-diethylthiacarbocyanine iodide Solution 2
3,3’-diethylthiadicarbocyanine iodide Solution 3
3,3’-diethylthiatricarbocyanine iodide Solution 4
What does alpha correct for? How well does alpha correct the wavelength?? What features of the spectrum indicate the formation of dimers and higher order aggregates? What happens upon dilution?
could you plz type the answer? not writing. thx. if you dont know what i am talking about u can see the lab in this link: https://chem.libretexts.org/LibreTexts/University_of_California_Davis/UCD_Chem_105/UCD_Chem_105%3A_Lab_Manual/Lab_7%3A_Conjugate_Dyes
Explanation / Answer
alpha values are related to the energies of different pi molecular orbitals in the conjugated systems (like the dyes listed here)
As the conjugation increases the energy gap between HOMO and LUMO decreases and the corresponding wavelength of the absorbtion for HOMO to LUMO transition increases. So as the conjugation increases alpha value decreases with a shift of wavelength to a higher value.
If dimesation or higher aggregates of the conjugated dyes are formed the conjugation increases resulting in the decrease in HOMO- LUMO energy gap and wavelength of maximum absorption shifts to a lower value.
According to Lambert - Beer's law, Absorbance value is directly proportional to the concentration. So upon dilution the absorbance of the solution decreases ( but the wavelength at which maximum absorbance happens remains fixed.)
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