Folding‐Induced Modulation of Excited‐State Dynamics in an Oligophenylene–Ethynylene‐Tethered Spiral Perylene Bisimide Aggregate

Abstract

The excited-state photophysical behavior of a spiral perylene bisimide (PBI) folda-octamer (F8) tethered to an oligophenylene-ethynylene scaffold is comprehensively investigated. Solvent-dependent UV/Vis and fluorescence studies reveal that the degree of folding in this foldamer is extremely sensitive to the solvent, thus giving rise to an extended conformation in CHCl(3) and a folded helical aggregate in methylcyclohexane (MCH). The exciton-deactivation dynamics are largely governed by the supramolecular structure of F8. Femtosecond transient absorption (TA) in the near-infrared region indicates a photoinduced electron-transfer process from the backbone to the PBI core in the extended conformation, whereas excitation power- and polarization-dependent TA measurements combined with computational modeling showed that excitation energy transfer between the unit PBI chromophores is the major deactivation pathway in the folded counterpart.

Ultrafast coherent exciton dynamics in size-controlled perylene bisimide aggregates

“…Under low concentrated conditions (i.e., below 1.0 × 10 −7 M) in a good solvating solvent (i.e., CHCl 3 ), the absorption spectra of both the ref-PBI monomer (bay-substitution) and the PBI 3 monomer (non-bay-substitution) show a vibrational progression over the S 0 –S 1 electronic transition coupled to the symmetric C-C vinyl stretching modes of the PBI core with approximately 1400 cm −1 (Fig. S1) 17,18 . In contrast, when PBI aggregates are formed in highly concentrated solutions in a poorly solvating solvent, the absorption spectra of a series of PBI aggregates exhibit a hypsochromic shift and broad spectral features resulting from the electronic interactions between the transition dipoles along the long axis of the π-stacked monomer 18 .…”

Using Fluorescence to Enable Innovative Functions of Foldamers

“…Time‐resolved fluorescence experiments measured the hole transfer rate through the oligoquinoline foldamer backbone in dichloromethane; these rates varied from 1×10 9 s −1 ( n =34) to 17×10 9 s −1 ( n =4). In related work, the photophysics of monodisperse foldamers that array perylene bisimide dyes on a phenylene ethynylene backbone ( 15 ) were studied in chloroform and in methylcyclohexane solutions using both steady state fluorescence and time‐resolved fluorescence experiments [47,48] . Correlations between foldamers’ extended or folded conformations and their mechanisms for relaxation of the dyes from their excited states were identified.…”

Photoinduced electron transfer (PET) versus excimer formation in supramolecular p/n-heterojunctions of perylene bisimide dyes and implications for organic photovoltaics

“…1,4-Dioxane was kept for several days over KOH, then reuxed with sodium and stored over 3 and 4 Å molecular sieves. The synthesis and characterization of monomeric PBI reference molecules N-(3-iodophenyl)-N 0 -(1-undecyldodecyl)perylene-3,4:9,10-tetracarboxylic acid bisimide (M1) 17 and N-[4,5-di-n-hexyl-1,2-(phenylethynylene)]-benzenefunctionalized N 0 -(1-undecyldodecyl)perylene-3,4:9,10-tetracarboxylic acid bisimide (M2), 17 folda-dimer F2, 17 and 4,5-di-n-hexyl-1,2-(phenylethynylene)-benzene backbone (B) 18 were reported recently. Column chromatography was performed on silica (silica gel, 230-400 mesh).…”

“…In contrast, our recent research interest has been dedicated to small model systems composed of electron-rich oligo-phenylene ethynylene backbones (p-type semiconductor molecules) with electron-poor perylene bisimides (PBIs; n-type semiconductor molecules) appended to them, whose supramolecular arrangement can be modulated between more random and more folded conformations by the chosen solvent. [16][17][18] Accordingly, photophysical properties can be compared for the same molecules in two states of different order, which is analogous to the situation in more crystalline and more amorphous bulk heterojunction OSC materials (Fig. 1).…”