Question

Dye - 1B 16 TT A T 28 2C Color Yollow Yellow ced Rod 476.35 Rod | 473.9 Rod | 461.77 Yollow 39.5 Amar (nm) 407.55 | 395.45 b. (0.5 points) How different are the colors of dyes 1A and 1B? (circle one) The same slightly different very different C. (0.5 points) How different are the colors of dyes 1A and 2A? (circle one) The same slightly different very different d. (1 point) What has a bigger effect on the color of the azo dye? (circle one) The number of aromatic rings The substitution pattern of the aromatic rings (ortho, meta, para) e. (4 points) Explain your answer to part d and include a description of how the structure of the dye affects the HOMO-LUMO gap. (point to specific experimental results that support your answer)

I just need help understanding question 4 and how structure affects homo-lumo gap.

Answer 1

Answer:Increasing the conjugation of double bonds(Aromatic rings) in dye always results in decreased HOMO-LUMO gap,this leads to the lower energy for absorption because HOMO-LUMO gap has decreased.In 1A conjugation of double bond is large in comparison to the 2C thus HOMO-LUMO gap is small in the case of 1A this leads to the higher wavelength for absorption(lower energy) in comparison to the 2C.

this effect is called Bathochromic shift in UV-Visible spectrum.The energy gap dividing the bonding and antibonding orbitals becomes progressively smaller with increasing conjugation.The increased conjugation shifts the observed wavelength of the absorption to higher values.