Emissive Organic Exciplexes in Water

Abstract

Unlike numerous known examples of exciplexes (products of charge formation reactions), we reported recently that cationic exciplexes (products of charge shift reactions) can be formed with N-methylisoquinolinium as an excited acceptor and alkyl benzene donors. We have now synthesized five intramolecular analogues (isoquinolinium linked by a trimethylene tether to alkyl benzenes) that proved to be well suited to demonstrating that emissive exciplexes can be formed in water from purely organic components. Three conformers (anti, gauche, and folded) leading to electron transfer were identified using a combination of absorption spectroscopy, fluorometry, and time-correlated single photon counting. The hydrophobicity of the donor moiety was found to enhance the formation of the folded conformer, which leads directly to exciplex formation. Electronic coupling matrix elements between ground, charge-transfer, and locally excited states were determined from correlations between radiative rate constants and average emission frequencies. The charge transfer (CT) character of the exciplexes (88–97%) was calculated from the electronic coupling. In spite of such a high CT character in a highly polar solvent, exciplex fluorescence quantum yields up to 0.03 and lifetimes up to 17 ns were observed.

Intra‐ and Intermolecular Fluorescence Quenching of Alkylthio‐Substituted Phthalimides by Photoinduced Electron Transfer: Distance, Position and Conformational Dependence

“…[29,30] This rule is valuable for the prediction of the most reactive substrate for intramolecular photochemical processes [31] or for the formation of intramolecular exciplexes. [32,33] The structural rationale of this empirical rule is the alkyl chain dynamics and the two X-ray structures analyses that we have determined for 3 (n = 3) and 14 a (n = 2) show, that the alkyl chain conformation has a gauche twist after the second tether carbon which favors donor-acceptor interaction especially in the n = 3 compound. Supposedly, a similar behavior exist in solutionphase that makes charge transfer processes efficient.…”

Cationic Exciplexes: Role of Hydrogen Bonding in Deactivation and Electronic Coupling

“…The distilled material was further heated with KMnO 4 /LiCO 3 (100°, 1 h) and then fractionally distilled. 1 + PF 6 − was prepared as previously described [2] …”

“…Cationic exciplexes are a new class of organic exciplexes in which the electron acceptor is a cation [1–3] . The excited state electron transfer to form these exciplexes represent charge shift reactions [Eq.…”

“…Cationic exciplexes expand the scope and potential applications of exciplexes, such as probing processes in highly polar solvents, including water [2] . We recently described solvent effects on the intramolecular cationic exciplex fluorescence of 1 + , which has a high degree of charge transfer character [3] .…”

Axially chiral 1,4-dihydropyridine derivatives: aggregation-induced emission in exciplexes and application as viscosity probes

“…This result is consistent with the increasing amount of conformation C, which leads to exciplex formation. 24,25 Meanwhile, we performed molecular dynamic simulations to study the conformational changes of (R)-2 in pure THF solution and in a THF/water mixture. The initial conguration Scheme 1 Synthetic routes for (R)-/(S)-2.…”