We report the enhanced fluorescence with the remarkably long lifetime (1.17 ns) in the first excited state (S 1) of highly crystalline molecular wires of azobenzene at the excitation wavelength of 467 nm for the first time. This observation suggests that trans-cis photoisomerization through the rotation or inversion mechanism may not be a favorable pathway after excitation to the S 1 state in highly single crystalline molecular wires of azobenzene due to the hindered motion within densely packed crystal structure. We also measured the fluorescence lifetime image of a single crystalline molecular wire of azobenzene, indicating that the lifetime was remarkably uniform and that there was only a very minor variation within the crystal.
Bibliographical noteFunding Information:
This work was supported by National Research Foundation of Korea Grant funded by the Korean Government (2010-0022028 and 2010-0541-1), and by the Ewha Global Top5 Grant 2011 of Ewha Womans University.