shown below.

least conjuated

As more rings $+$ conjugation are added to the structure, the snectra are red$-$Shlfted further into the visible region

$15.$ The peaks in the UV absorbance spectrum of pyridine are noticeably blue$-$shifted when changing the solvent from hexane $(C_6{H}_{14})$ to methanol $(C{H}_{3}OH),$ while the peaks in the spectrum for benzene are only slightly red$-$shifted. What may be causing this difference in behavior?

blue$-$shift is seen when the solvent is changed from hexane to methanol with pyridine because of the ability of pyridine to nydrogen$-$bond wits methanol. Benzene can't hydrogen bond