US EPA

7942760 

Journal Article 

The quenching of short-lived S-2 states of aromatic thioketones by hydrocarbons .1. Important contributions of the transient effect from steady-state measurements 

Maciejewski, A; Sikorski, M; Augustyniak, W; Fidecka, M 

1996 

Yes 

Journal of Photochemistry and Photobiology A: Chemistry
ISSN: 1010-6030
EISSN: 1873-2666 

94 

2-3 

119-127 

English 

10.1016/1010-6030(95)04199-0 

WOS:A1996UE06400006 

The very efficient fluorescence quenching of seven aromatic thioketones in the second excited singlet state S2 (lifetime τS2, = 53-857 ps in inert perfluoro-1,3-dimethylcyclohexane) has been examined by quantum yield and/or intensity measurements. Five n-alkanes (C6H14, C8H18, C8D18, C10H22 and C16H34) as well as 2,2,4,4,6,8,8-heptamethylnonane, cyclohexane, benzene and their deuterated derivatives were used as quenchers. The contribution of the transient effect to the quenching rate constant kq, which depends on the S2-thioketone lifetime as well as on the size and diffusion coefficient of the quencher, has been investigated. The role of the transient effect in the quenching process was found to be very significant. Taking the transient effect into account, the quenching rate constants calculated from the Stern-Volmer relation ranged from 0.2 × 1010 M-1 s-1 to the very large value of 12 × 1010 M-1 s-1. These experimental results have been rationalized by assuming the Smoluchowski-Collins-Kimball model. A comparison has been made between the measured and calculated values of kq for almost 40 donor-quencher systems in perfluoro-1,3-dimethylcyclohexane. 

quenching; S-2 states; aromatic thiketones; steady-state measurements