Ultrafast Resonance Energy Transfer in Ethylene-Bridged BODIPY Heterooligomers: From Frenkel to Förster Coupling Limit

Abstract

A series of distinct BODIPY heterooligomers (dyads, triads, and tetrads) comprising a variable number of typical green BODIPY monomers and a terminal red-emitting styryl-equipped species acting as an energy sink was prepared and subjected to computational and photophysical investigations in solvent media. An ethylene tether between the single monomeric units provides a unique foldameric system, setting the stage for a systematic study of excitation energy transfer processes (EET) on the basis of nonconjugated oscillators. The influence of stabilizing β-ethyl substituents on conformational space and the disorder of site energies and electronic couplings was addressed. In this way both the strong (Frenkel) and the weak (Förster) coupling limit could be accessed within a single system: the Frenkel limit within the strongly coupled homooligomeric green donor subunit and the Förster limit at the terminal heterosubstituted ethylene bridge. Femtosecond transient-absorption spectroscopy combined with mixed quantum-classical dynamic simulations demonstrate the limitations of the Förster resonance energy transfer (FRET) theory and provide a consistent framework to elucidate the trend of increasing relaxation lifetimes at higher homologues, revealing one of the fastest excitation energy transfer processes detected to date with a corresponding lifetime of 39 fs.

One-Pot Access to Ethylene-Bridged BODIPY Dimers and Trimers through Single-Electron Transfer Chemistry

“…The narrowed absorption and emission line widths as well as the red-shifted maxima for the dimers and trimers are in line with the characteristics of J -type aggregations, which are in agreement with the unique features of ethylene-bridged J -aggregating oligo-BODIPYs reported by Werz group . Furthermore, support came from the solid-state crystal structure of dimer 2a (Figure ).…”

“…Electrophilic attack of the 3,5-methyl groups with NBS was reported and was useful for further transformation . Recently, Werz and co-workers used LDA as a base to deprotonate the 3-methyl group at −78 °C (Figure b) and thus developed a versatile and rapid access to give ethylene-bridged BODIPY oligomers with the addition of 0.5 equiv of ICl . These nonconjugated oligo-BODIPYs showed interesting J -type excitonic coupling, outstandingly high attenuation coefficients, and intense fluorescence.…”

Interface Engineering of Bi‐Fluorescence Molecules for High‐Performance Data Encryption and Ultralow UV‐Light Detection

“…Organic emitters with the dynamic ability to tune emission colors from different excited states in response to external stimuli, such as optical excitation, mechanical force, and pressure exhibit high potential in life science, energy conversion, and safety engineering. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] However, it is extremely difficult, selectively excited (Figure 1b). By varying the excitation energies from 4.27 eV (290 nm) to 3.44 eV (360 nm), the emission color of the OA-DFBK composites was deterministically tuned from deep blue to green in the spectral range.…”

“…Organic emitters with the dynamic ability to tune emission colors from different excited states in response to external stimuli, such as optical excitation, mechanical force, and pressure exhibit high potential in life science, energy conversion, and safety engineering. [ 1–16 ] However, it is extremely difficult, if not impossible, to achieve such a tunability due to the difficulty in separating large energies and the stability of different electronic excited states. [ 17–21 ] Therefore, it remains a challenge to precisely control the luminescence of organic chromophores from different electronically‐excited states.…”

Femtosecond Spectroscopy and Nonlinear Optical Properties of aza‐BODIPY Derivatives in Solution

“…For example, specific light‐induced electron‐transfer stages in the intramolecular relaxation processes allows optical gain in the system for certain wavelengths. The possibility to realize extremely fast energy transfer processes (∼40 fs) in BODIPY‐based oligomer structures was recently reported in ref [13] . as a potential mechanism for optoelectronic applications.…”