Excimer Formation and Symmetry-Breaking Charge Transfer in Cofacial Perylene Dimers

Abstract

The use of multiple chromophores as photosensitizers for catalysts involved in energy-demanding redox reactions is often complicated by electronic interactions between the chromophores. These interchromophore interactions can lead to processes, such as excimer formation and symmetry-breaking charge separation (SB-CS), that compete with efficient electron transfer to or from the catalyst. Here, two dimers of perylene bound either directly or through a xylyl spacer to a xanthene backbone were synthesized to probe the effects of interchromophore electronic coupling on excimer formation and SB-CS using ultrafast transient absorption spectroscopy. Two time constants for excimer formation in the 1-25 ps range were observed in each dimer due to the presence of rotational isomers having different degrees of interchromophore coupling. In highly polar acetonitrile, SB-CS competes with excimer formation in the more weakly coupled isomers followed by charge recombination with τ = 72-85 ps to yield the excimer. The results of this study of perylene molecular dimers can inform the design of chromophore-catalyst systems for solar fuel production that utilize multiple perylene chromophores.

Electron‐Deficient Bipyrrole Boomerangs: Bright Fluorophores Obtained via Double C−H Bond Activation

“…This dependence on n and the bichromophoric structure of the boomerangs indicate the potential symmetrybreakingc haracter of the ICT. [23][24][25][26][27][28][29][30] In the above set of solvents, the F fl valueso fcNMI1 EE did not vary significantly (60-67 %), whereas the emissionso f cNMI2 EE and cNMI3 EE were enhanced in benzonitrile( 58 %a nd 48 %, respectively,v s. 32 %a nd 31 %i nt oluene). The observed reduction of the radiative rate constant (k r )o fcNMI1 EE in more polar solvents, attributed to the corresponding decrease of electron-hole overlap in the CT state, is balanced by ar eduction of the nonradiative constant (k nr ), whichm akes F fl almost independento fs olvation effects.…”

“…The difference in S 0 and S 1 dipole moments becomes larger with increasing n , indicating that the effect may be enhanced by the increased out‐of‐plane distortion of the chromophore. This dependence on n and the bichromophoric structure of the boomerangs indicate the potential symmetry‐breaking character of the ICT …”

Tuning symmetry breaking charge separation in perylene bichromophores by conformational control

“…More recently, several groups investigated pstacked bichromophores, either covalently linked with stiff backbones or designed for self-assembly, and allowing for precise control of mutual geometry. [47][48][49][50][51] These studies were mostly limited to closely p-stacked conformations and the differences in the dynamics and the nature of the excited states between the various structures were rather subtle.…”

Discrete Dimers of Redox-Active and Fluorescent Perylene Diimide-Based Rigid Isosceles Triangles in the Solid State

“…It is evident that the spectra at the early time delays correspond to the S 1 state(Figure 6a). Significantly, after about 3 ps, the peaks in the 600-800 nm ESA region are flattened, which is a signature[67][68] of excimer formation. All transient signals then decay back to S 0 in 7 ns.…”