The interplay of different relaxation channels in the excited state dynamics of photoinitiators

Abstract

Abstract. Different photoinitiators are investigated by femtosecond transient absorption spectroscopy and DFT calculations. Their initiation properties are critically governed by competition between intersystem crossing, fluorescence and internal conversion partly taking place on comparable time scales. It is thereby shown that the S* lifetime cannot serve as a measure for the photoinitiation efficiency.

Quantifying Photoinitiation Efficiencies in a Multiphotoinitiated Free‐Radical Polymerization

“…However, earlier studies from our laboratories have demonstrated that such a correlation does not generally hold as a strong origin dependence can apply: Mesitoyl radicals (4) derived from mesitil show a much poorer incorporation propensity than benzoyl radicals (1) derived from benzoin (A), although mesitil features a 10 times stronger absorbance than benzoin (A) at 351 nm 10, 11. The origin of such different behavior lies in the molecular structure of the employed photoinitiators: UV absorbtivity and initiation ability only correlate well for molecules of the same general type (here benzoin‐type), yet do not correlate when molecules with different intersystem crossing abilities are employed, as we will demonstrate in a forthcoming publication 20…”