Photoinduced Interactions in a Pyrene-Calix[4]arene-Perylene Bisimide Dye System: Probing Ground-State Conformations with Excited-State Dynamics of Charge Separation and Recombination

Abstract

A calix [4]arene scaffold has been functionalized with an electron-accepting perylene bisimide as well as an electron-donating pyrene unit. Steady-state and time-resolved spectroscopy indicate a strong charge-transfer (CT) interaction between these two units in all investigated solvents. The signatures of the radical anion of the perylene bisimide and the radical cation of the pyrene are observed with femtosecond transient absorption spectroscopy. A preferential π-stacked conformation is inferred. In tetrahydrofuran as a solvent ∼25% of an extended form is invoked. The CT states of these two ground-state populations (π-stacked and extended) have different formation and decay kinetics and result in the spectral distinction of a compact and an extended charge-transfer state upon visible excitation. In the extended conformation, upon UV excitation, pyrene acts as an electron acceptor that is reduced through a photoinduced electron-transfer process by the calix[4]arene. In this conformation the calixarene scaffold is accordingly not an uninvolved linker unit but participates effectively in the electron-transfer processes.

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

“…By shifting the probe wavelength to the near‐infrared (NIR) region, we can acquire an in‐depth understanding on the process responsible for the rigorously quenched fluorescence of F8 , that is, the PET process. As the formation of PBI radical anions is easily recognized by an decrease of neutral PBI absorption in the 425–550 nm region and a concomitant increase of new absorption bands at 713, 800, and 960 nm,5b, 7b, 28 we focused our attention on the ESA signals, which should contain the spectral signature of absorption from the PBI radical anion (PBI ⋅− ) formed during the photoinduced charge separation (CS) process.…”

Excitation Dynamics in Hetero‐bichromophoric Calixarene Systems

“…[1,2,7,[19][20][21][22][23][24][25][26][27][28] Herein, we present the synthesis and characterization of af amily of covalent bichromophorics ystemsa ble to efficiently perform intramolecular energy transfer from the donort ot he acceptorchromophore.The chosen central scaffold is acalix [4]arene macrocycle, which is particularly suited for our purposes, as it could be functionalized with severalm oieties positioned at aw ell-definedd istance and orientation.C alixarenes have been previously used as convenient scaffolds for chromophores acting as fluorescent probes, and af ew examples are reported for which energy transfer between two or more linked chromophores was investigated. [29][30][31][32][33] In our case, two well-known dyes, 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) and am odified Nile Red (NR), were selected as energy-donor and energy-acceptor units,r espectively,a nd linked at the 1,3-distal positions of the upper rim of acone and apartial cone calix [4]arene derivative to obtain af amily of three hetero-bichromophoric systems (Scheme 1). [34] The two different geometries, cone and partial cone, of the calixarene scaffold direct the two chromophores to the same and opposite sides, respectively.…”

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

“…Upon fluorescence titration, the intrinsic emission of Fl was drastically quenched by gradual addition of GC5A. Given calixarenes as well-demonstrated fluorescence quenchers acting through a photoinduced electron transfer (PET) mechanism [8,28–29], we hypothesize an electron transfer-induced quenching in the GC5A–Fl complex as underlying mechanism. The binding stoichiometry between GC5A and Fl was determined to be 1:1 according to the Job's plot.…”