Mechanism and deactivation kinetics of S2-xanthione in acetonitrile, a quenching solvent, and of S2-exciplex measured by pico- and femtosecond laser spectroscopy

Proton Transfer Reactions in the Excited Electronic State

“…As a rule, such processes are studied without taking into account highest excited states. At the same time, as was shown, for example, in Refs [97] and [98], the role of high-lying singlet states is not confined only to processes of intramolecular internal conversion. Very frequently, both initial excited molecules and products of their photoreactions exhibit pronounced luminescence; in this case, luminescence methods are very effective and are widely used in various fields of physics, chemistry and biology [73-75, 88, 99].…”

Ultrafast quenching of the excited S2 state of benzopyranthione by acetonitrile

“…The formation of a S 2 state solutesolvent exciplex has been suggested as the intermolecular interaction responsible for the XT S 2 state quenching process. A very weak transient absorption signal, observed after subtraction of the S 2 and T 1 absorption bands, has been tentatively attributed to this exciplex [7]. The purpose of the present work is to extend this study to the case of BPT and determine whether the formation of such an exciplex can be confirmed or not.…”

“…The long S 2 state lifetime of thioketones (s S 2 ¼ 10 À9 -10 À11 s), due to a large DEðS 2 À S 1 Þ energy gap, is responsible for the S 2 -state fluorescence, whereas emission from the S 1 state (radiative rate constant of about 10 5 s À1 ) is insignificant due to an ultrafast intersystem crossing process to the T 1 state (s S 1 % 10 À12 s) [4]. The S 2 state is known to be extremely reactive in solution because of efficient intermolecular quenching by most solvents including acetonitrile, but except perfluorohydrocarbons (PF) in which the S 2 state decay is exclusively intramolecular [1,3,[5][6][7][8]. Recently, we have reported an analysis of the quenching mechanism of the S 2 state of 4H-1-benzopyrane-4-thione (BPT) by hydrocarbons using femtosecond transient absorption spectroscopy [9].…”

“…The quenching of the S 2 state of thioketones by acetonitrile has been investigated only for xanthione (XT) from picosecond emission (time-correlated single photon counting) and femtosecond transient absorption measurements [5,7]. The formation of a S 2 state solutesolvent exciplex has been suggested as the intermolecular interaction responsible for the XT S 2 state quenching process.…”

Tetraalkylammonium Salts of Amino Acids and Sulfur‐Containing Amino Acids as Effective Co‐Initiators of Free Radical Polymerization in the Presence of Aromatic Ketones

“…For more detailed information, see the papers published by Maciejewski et al [27] and cited therein. [24] A large red shift is observed in the fluorescence wavelength maximum with increasing polarity of the solvents, from hexane to ethanol.…”