Answer to Question #116642 in Physical Chemistry for Ayesha

Question

Explain the wavelength dependent photochemistry of benzene derivatives.

Answer 1

The possible reasons of wavelength dependent photochemistry of benzene derivatives can be divided in wavelength-dependent and wavelength-selective reactions. The first class refers to the reactions where the same products are formed, and only the efficiency (quantum yield) changes upon the different excitation wavelength. The most evident explanation of such a behavior is the absorption coefficient change[1]. However, a very different dependence was shown for oxime ester derivatives [2].

The second class (wavelength-selective) refers to the reactions which fate is different upon the excitation wavelength. The wavelength-selective reactions result when a photon of different wavelength:

(i) activates a different chromophore in a single molecule (chromatic othogonality),

(ii) induces the population of different reactive excited states (state selectivity)

(iii) sequentially populates the excited state of a compound and the excited state of an intermediate photogenerated from it, which show a different reactivity [3].

The state selectivity example for acetaminophen photolysis is available in literature[4]:

.

References:

[1] J. Chem. Educ. 2020, 97, 2, 543-548

[2] Macromolecules 2017 50 (5), 1815-1823

[3] Photochem. Photobiol. Sci., 2019,18, 2094-2101

[4] Journal of Photochemistry and Photobiology A: Chemistry 274 (2014) 117–123