| Summary: | 碩士 === 國立清華大學 === 化學系 === 95 === Using three techniques including time-correlated single photon counting, femtosecond fluorescence up-conversion and femtosecond transient absorption we study the molecular energy transfer between donor and acceptor. Five molecules [(1,1'-biphenyl)-4,4'-diyldi-2,1-ethenediyl]bis(dimethylsilane) (monomer D 1), [1,2-ethenediylbis(4,1-phenylene-2,1-ethenediyl)]bis(dimethylsilane) (monomer A 2), and copolymers [(Donor-SiMe2)n = 1-3-(Acceptor-SiMe2)]m, 1D1A 3, 2D1A 4 and 3D1A 5 are used. Upon excitation at 266 nm monomer D 1 exhibits bi-exponential behavior on its fluorescence decay curve with the fitted time constants 81.7 ± 4.2 ps and 681.2 ± 37.5 ps. We assign the short component to be the lifetime of the S2 state and the long one to be the S1 state. Following excitation of 375 nm on monomer A 2, it exhibits single exponential decay with a time constant 976.3 ± 11.8 ps. Accordingly we assign that to be the lifetime of the S1 state of A 2. For the copolymers 1D1A 3, 2D1A 4, and 3D1A 5, all of them exhibit biexponential fluorescence decay with fitted fast and slow lifetimes 118.2 ps, 836.7 ± 18.8 ps, 118.5 ps, 873.0 ± 3.0 ps, and 85.1 ps, 824.0 ± 2.0 ps, respectively. We assign the short component to be vibrational relaxation of the excited states of copolymers, and the long component to be the lifetime of the S1 state. The data recorded with the transient absorption spectrometer display an absorption band of D* 1 centered at 660 nm and of A* 2 at 450 nm, respectively. For all three copolymers the rise of A* 2 appearance is faster than (5ps)-1 indicating that the energy from donor to acceptor is very efficient.
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