A femtosecond (fs) broad-band absorption apparatus was used to measure the early photoisomeriza-tion process of bacteriorhodopsin’s (BR) photocycle to reveal the character of the important interme-diate of J625 and to obtain a deeper understanding of the role of photoisomerization in BR photocycle. Two time constants of 0.5 ps (95%) and 2.0 ps (5%) were brought out by global fitting on thirty curves in the near-infrared region. We suggest that the first time constant results from the decay of I460 interme-diate,and the longer component might be associated with BR isomer. The global analysis over 450,540,630,710 and 870 nm traces identified two time constants,～0.5 and～3 ps. The slower component can be extracted from the processes of both J625→BR568 (540 nm) and J625→K590 (630 nm),suggesting J-in-termediate takes a partial cis configuration. The obvious negative feature in early delay time of 700―780 nm regions was attributed to the radiative transition (stimulated emission) from the Franck-Condon active configuration along the isomerization potential surface of all-trans-retinal.
Eu(TTA)3DPBT was found most likely to lead a special singlet photosensitization pathway by means of time-resolved luminescence spectroscopic studies.For further understanding of its intra-molecular energy transfer mechanism,another lanthanide complex Eu(TTA)3BDDT was synthesized,using a related ligand BDDT,changing the D-π-A structure of DPBT to the D-A structure of BDDT.The luminescence characteristics of both complexes were investigated and compared.Results show that π bridge plays an important role in the energy transfer process.π bridge can change the charge separation strength by affecting the electron-density distribution over the diethylaniline and the dipyrazoletriazine moieties.Without the π bridge connection,the benzene ring,BDDT gets a smaller conjugated system,and the absorption peak in the UV-Vis spectrum of BDDT has a blue shift of 114 nm relative to that of DPBT.So the energy level of ligand BDDT and the central ion Eu(Ⅲ) does not match well,and the energy transfer efficiency drop 33%.
