TY  - GEN
N2  - The phenomena of photo-induced chemical reactions can exhibit kinetics as short as a few femtoseconds. The development of femtosecond UV pulses enables the investigation of such ultrafast phenomena in more experimentally challenging, UV absorbing systems. This thesis describes, chronologically, development of a UV transient absorption (TA) system and its application to various coumarin-based molecular systems. The experimental section details the TA system comprising of three major components: two tunable UV excitation sources giving a total excitation range of 250-350 nm, supercontinuum generation enabling 240-700 nm probe range, and multichannel detection with greater than 5 ×10-5 OD sensitivity. The potential of the TA setup was tested on the study of ultrafast relaxation in 7-hydroxy coumarin.  Following successful tests, the photo-induced cleavage reaction of coumarin dimer was studied in order to understand the ultrafast dynamics. The experiments utilized 280 nm excitation and broadband (300-650 nm) probing. The results revealed fast cleavage occurring through short-lived nonradiative (<200 fs) singlet states. Two branched kinetic models were developed to describe the monomer formation and dimer relaxation dynamics, identify intermediate states, and determine the quantum yields. The anti-hh displayed the highest cleavage efficiency of ~20 %.  Finally, variation in the quantum yields between isomers was rationalized using a sequential bond cleavage mechanism over a concerted, ?pericyclic-style? ring cleavage.
A1  - Jiang, Man
AV  - public
TI  - Femtosecond UV Transient Absorption Study of Coumarin Dimers
Y1  - 2017///
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/22677/
ID  - heidok22677
ER  -