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Which mechanism initiates photoisomerization of retinal in rhodopsin?

A)π to π* orbital transition
B)Vibrational energy level relaxation
C)Excitation of a sigma orbital
D)Hydrogen bond formation with opsin

💡 Explanation

The *cis*-to-*trans* isomerization occurs because photon absorption promotes an electron to a higher energy π* orbital, via **photoexcitation**, weakening the double bond. Therefore, the molecule can twist easily, rather than via vibrational modes or strong bonds with opsin.

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