Single molecule aggregation-induced dual and white-light emissive etherified aroyl-S,N-ketene acetals via one-pot synthesis

Etherified aroyl-S,N-ketene acetals are readily synthesized by a novel one-pot addition-elimination-Williamson-etherification sequence. Although the underlying chromophore remains constant, derivatives show pronounced color-tuning of solid-state emission and AIE characteristics, whereas a hydroxy-methyl derivative represents an easily accessible mono molecular aggregation-induced white-light emitter.

Asymmetrically bridged aroyl-S,N-ketene acetal-based multichromophores with aggregation-induced tunable emission

Asymmetrically bridged aroyl-S,N-ketene acetals and aroyl-S,N-ketene acetal multichromophores can be readily synthesized in consecutive three-, four-, or five-component syntheses in good to excellent yields by several successive Suzuki-couplings of aroyl-S,N-ketene acetals and bis(boronic)acid esters. Different aroyl-S,N-ketene acetals as well as linker molecules yield a library of 23 multichromophores with substitution and linker pattern-tunable emission properties. This allows control of different communication pathways between the chromophores and of aggregation-induced emission (AIE) and energy transfer (ET) properties, providing elaborate aggregation-based fluorescence switches.

A library of 23 asymmetrically linked aroyl-S,N-ketene acetal solid-state emissive multichromophores accessed by one-pot multicomponent reactions exhibits AIE- and AIEE-active behavior as well as dual emission and potential energy transfer.

Communication of Bichromophore Emission upon Aggregation - Aroyl-S,N-ketene Acetals as Multifunctional Sensor Merocyanines

Aroyl-S,N-ketene acetal-based bichromophores can be readily synthesized in a consecutive three-component synthesis in good to excellent yields by condensation of aroyl chlorides and an N-(p-bromobenzyl) 2-methyl benzothiazolium salt followed by a Suzuki coupling, yielding a library of 31 bichromophoric fluorophores with substitution pattern-tunable emission properties. Varying both chromophores enables different communication pathways between the chromophores, exploiting aggregation-induced emission (AIE) and energy transfer (ET) properties, and thus, furnishing aggregation-based fluorescence switches. Possible applications range from fluorometric analysis of alcoholic beverages to pH sensors.

One-pot synthesis of a white-light emissive bichromophore operated by aggregation-induced dual emission (AIDE) and partial energy transfer

Consecutive four-component insertion–alkynylation–amination–Suzuki sequence furnishes bichromophores that emit white light upon aggregation-induced dual emission (AIDE) operating by partial energy transfer between the constituting chromophores.

Ultrafast excitation energy transfer in a benzimidazole-naphthopyran donor-acceptor dyad

The excited-state dynamics of a donor-acceptor dyad composed of 1-propyl-2-pyridinyl-benzimidazole (PPBI) as donor and the photochromic molecular switch diphenylnaphthopyran (DPNP) as acceptor linked via an ester bridge has been investigated by a combination of static and time-resolved spectroscopies and quantum chemical calculations. The UV absorption spectrum of the dyad is virtually identical to the sum of the spectra of its individual constituents, indicating only weak electronic coupling between the donor and acceptor in the electronic ground state. After selective photoexcitation of the PPBI chromophore in the dyad at λpump = 310 nm, however, a fast electronic energy transfer (EET) from the donor to the acceptor is observed, by which the lifetime of the normally long-lived excited state of PPBI is reduced to a few ps. Enabled by the EET, the acceptor switches from its ring-closed naphtopyran form to its ring-opened merocyanine form. The singular value decomposition-based global analyses of the measured femtosecond time-resolved transient absorption spectra of the dyad and its two building blocks as reference compounds allowed us to determine a value for the EET time constant in the dyad of τ = 2.90 ± 0.60 ps. For comparison, Förster theory predicts characteristic FRET times between 1.2 ps ≤ τ ≤ 4.2 ps, in good agreement with the experimental result.

Diversity-Oriented Synthesis and Optical Properties of Bichromophoric Pyrrole-Fluorophore Conjugates

The mild reaction conditions of the palladium-copper coupling-isomerization reaction open a highly convergent, chromogenic route to blue emissive pyrroles in the sense of a consecutive four-component reaction. By virtue of this strategy a phenol derivative can be readily accessed, which can be transformed in a level-2 transformation to a library of bichromophoric pyrrol-fluorophore conjugates by facile alkylation with fluorophore halides. The photophysics of the underlying blue emitter derivative and the conjugates is studied by absorption and emission spectroscopy, furnishing intramolecular energy transfer at short distances as well as competing fluorescence quenching. In some cases partial energy transfer results in the occurrence of dual emission, for instance seen as magenta-rose emission arising from blue and red orange luminescence. The experimental photophysical studies are rationalized by DFT and TD-DFT calculations.

Excitation Dynamics in Hetero-bichromophoric Calixarene Systems

In this work, the dynamics of electronic energy transfer (EET) in bichromophoric donor-acceptor systems, obtained by functionalizing a calix[4]arene scaffold with two dyes, was experimentally and theoretically characterized. The investigated compounds are highly versatile, due to the possibility of linking the dye molecules to the cone or partial cone structure of the calix[4]arene, which directs the two active units to the same or opposite side of the scaffold, respectively. The dynamics and efficiency of the EET process between the donor and acceptor units was investigated and discussed through a combined experimental and theoretical approach, involving ultrafast pump-probe spectroscopy and density functional theory based characterization of the energetic and spectroscopic properties of the system. Our results suggest that the external medium strongly determines the particular conformation adopted by the bichromophores, with a direct effect on the extent of excitonic coupling between the dyes and hence on the dynamics of the EET process itself.

DFT/TDDFT investigation on the UV-vis absorption and fluorescence properties of alizarin dye

Potential energy curve for the ESIPT. Top inset: vibrationally resolved emission spectra computed for both tautomers. Bottom insets: main vibrational modes.