Importance of Properties of the Lowest and Higher Singlet Excited States on the Resonant Two-Photon Ionization of Stilbene and Substituted Stilbenes Using Two-Color Two-Lasers

Abstract

Radical cations of trans-stilbene and substituted trans-stilbenes (stilbenes and the radical cations denote Sand S(*+), respectively) were generated from the resonant two-photon ionization (TPI) in acetonitrile with irradiation of one-laser (266- or 355-nm laser) and with simultaneous irradiation of two-color two-lasers (266- and 532-nm or 355- and 532-nm lasers) with the pulse width of 5 ns each. The formation yields of S(*+), the TPI efficiency, depended on the properties of S in the lowest and higher singlet excited state (S(S(1)) and S(S(n))), generated from one-photon excitation with 266- or 355-nm laser and from two-photon excitation with simultaneous irradiation of 266- and 532-nm or 355- and 532-nm lasers, respectively. The TPI efficiency using two-color two-lasers increased compared with that using one-laser. It is confirmed that the TPI proceeds through two-step two-photon excitation with the S(0) --> S(1) --> S(n)() transition. In addition to the electronic character of S(S(0)) which depends on the substituent of S, oxidation potential, and molar absorption coefficient of the S(0) --> S(1) absorption as well-known important factors for the TPI efficiency, it is shown that properties of S(S(1)) and S(S(n)) such as lifetimes, electronic characters of S(S(1)) and S(S(n)), molar absorption coefficient of the S(1) --> S(n) absorption, and ionization rate from S(S(n)) are also important.

Highly efficient green-light ionization of an aryl radical anion: key step in a catalytic cycle of electron formation

“…Of the very few known monophotonic green-light ionizations in polar solvents, 35,[41][42][43][44] that of the doubly deprotonated terephthalate radical anion has the highest quantum yield (j ion = 0.07) 35 reported so far. The system studied in the present work constitutes a very significant advance because j ion is four times as high for it, which compares favourably with the quantum yields of the most efficient UV photoionizations known to date, 6 although the energy of the ionizing photon is lower by almost 200 kJ mol À1 .…”

Immobilization and Continuous Recycling of Photoredox Catalysts in Ionic Liquids for Applications in Batch Reactions and Flow Systems: Catalytic Alkene Isomerization by Using Visible Light

“…Stilbene and derivatives represent broadly applicable molecules which show characteristic absorption and fluorescence due to their conjugated π‐system and can therefore be photochemically excited 1. Owing to these properties such olefins are important additives in the production of industrial dyes,2 chromatic lasers3 and scintillators 4…”

An “All‐Green” Catalytic Cycle of Aqueous Photoionization

“…[1] Having in mind the ultimate aim of utilizing the sun as the (low-flux) light source, it is the most promising strategy to employ two successive single-photon absorptions and store the energy of the first photon in an intermediate. Examples of electron detachment by green light are known for all common classes of photochemical intermediates, excited singlet states, [2] triplet states, [3,4] radicals, [5][6][7] and radical anions, [8][9][10][11][12] but the longer such an intermediate lives, the more likely it is to absorb the ionizing second photon. This suggests that the usefulness for this process increases in the order excited singlet (ns) < triplet (ms) < radical or radical anion (no photophysical deactivation).…”