Halogen-Bond Assisted Photoinduced Electron Transfer

Abstract

The formation of a halogen-bond (XB) complex in the excited state was recently reported with a quadrupolar acceptor–donor–acceptor dye in two iodine-based liquids (J. Phys. Chem. Lett. 2017, 8, 3927–3932). The ultrafast decay of this excited complex to the ground state was ascribed to an electron transfer quenching by the XB donors. We examined the mechanism of this process by investigating the quenching dynamics of the dye in the S1 state using the same two iodo-compounds diluted in inert solvents. The results were compared with those obtained with a non-halogenated electron acceptor, fumaronitrile. Whereas quenching by fumaronitrile was found to be diffusion controlled, that by the two XB compounds is slower, despite a larger driving force for electron transfer. A Smoluchowski–Collins–Kimball analysis of the excited-state population decays reveals that both the intrinsic quenching rate constant and the quenching radius are significantly smaller with the XB compounds. These results point to much stronger orientational constraint for quenching with the XB compounds, indicating that electron transfer occurs upon formation of the halogen bond.

Synthesis of Novel 1,4-dihydro-1,2,4,5-tetraarylpyrrolo[3,2-b]pyrroles Derivatives Catalyzed by NbCl5 and Application in Dye Sensitized Solar Cells

“…In recent years progress has been achieved through theoretical and experimental studies of photoelectronic properties and applications. The 1,4-dihydro-1,2,4,5-tetraarylpyrrolo [3,2-b] pyrroles usually have high absorption and emission in UV-vis region, and some investigations were made using various substituents on their aryl rings, showing good electronic communication between the pyrrolo [3,2-b]pyrrole donor center and both the N-aryl and the C-aryl groups 4,5,7 , with possibility of symmetry breaking of the excited state [17][18][19][20][21] , aggregation-induced and solid state emission [22][23][24][25][26] and two-photon absorption [27][28][29] .…”