Studies of Excited-State Properties of Multibranched Triarylamine End-Capped Triazines

Electron donor-acceptor types of multibranched triarylamine end-capped triazines have been systematically investigated by steady-state electronic spectroscopy, electrochemistry, femtosecond fluorescence anisotropy and solvent relaxation dynamics. The results, together with computational approach, have gained in-depth insight into their excited-state properties, especially the interactions between branches. Among different branched triarylamines of one, two and three arms, the interbranch interaction between each arm is weak, as evidenced by their nearly identical absorption spectral profile and frontier orbitals analyses. Upon S-0 -> S-1 excitation, the electronic delocalization in the three-branched triarylamine end-capped triazine is resolved to be 680 +/- 130 fs, followed by a slow (28 +/- 3 ps) electronic localization into one branch and consequently a rotational depolarization of 2.0 +/- 0.1 ns. Similar delocalization dynamics was resolved for the two-branched triarylamine end-capped triazine (electronic delocalization, 500 +/- 90 fs; twisting localization, 21 +/- 5 ps; rotational depolarization, 700 +/- 30 ps). The comparable electron delocalization and solvent relaxation time scale may set up a new paradigm to investigate their specific correlation in the early time domain.