Proton-assisted interaction between luminescent species containing diazacrown ethers and anthryl chromophores

Abstract

The multicomponent species 1 and 2 (structural formulas shown in Fig. 1), made of diazacrown receptors and anthracene-based chromophores, have been synthesized, together with 3, an already-known species containing the anthracene chromophore and an appended amino group. The absorption spectra and luminescence properties of 1-3 have been studied in acetonitrile solution, both in the absence and presence of protons. All of the compounds exhibit luminescence, the intensity of which is enhanced in the presence of protons, and have the role of inhibiting the reductive electron transfer emission quenching processes operating in non-protonated 1-3. The emission intensity of an equimolar solution of 1 and 3 is increased by proton addition, as expected, however the maximum of the intensity is reached when acid concentration is about 1.5 times higher than those of 1 or 3. This suggests that proton-assisted interaction between 1 and 3 takes place. The equimolar solution of 2 and 3 exhibits two emission features, each one assigned to a component chromophore. Low acid concentration leads to enhancement of the 400 nm emission, related to the species 3, and higher acid concentration allows for enhancement of the 520 nm emission, related to the species 2. A closer observation of the luminescence titration curve, as well as NMR data, indicates that a 2?3 adduct is present even before proton addition, and the adduct is further stabilized by protonation to form 2?H?3.

Bifunctional Charge Transfer Operated Fluorescent Probes with Acceptor and Donor Receptors. 2. Bifunctional Cation Coordination Behavior of Biphenyl-Type Sensor Molecules Incorporating 2,2‘:6‘,2‘ ‘-Terpyridine Acceptors

“…Different types of systems that perform logical operations with chemical inputs and provide optical outputs have been reported up to now including, e.g., AND, OR, NOR, INHIBIT, YES, and NOT logic gates. These devices are typically ET-operated and respond to combinations of protons and alkali or alkaline earth metal ions. , In contrast to the general interest in systems that undergo clearly distinguishable changes of different measurable fluorescence parameters specific for a certain chemical input, examples for CT-operated logic gates are comparatively rare. , As has been suggested by the protonation studies detailed in part 1 of this series 38 and the previously discussed spectroscopic properties of A-coordinated, D-coordinated, and A- and D- coordinated bpb-DMA and bpb-A15C5, principally, CT-operated biphenyl-type molecules with integrated A- and D-receptors seem to be suited for logic operation with the proper choice of the absorption, excitation, and emission wavelengths due to their strong input-controlled changes in intensity, energy, and fluorescence lifetime. , For this type of application, however, future developments of the bpb-R series need to be directed toward more selective receptors. One ongoing approach is the substitution of the terpyridine acceptor receptor for a more selective one, e.g., a 2,6-bis(2-thienyl)pyridine binding site. , In any case, like many other fluorescent reporters and molecular switches undergoing chelation-induced fluorescence quenching, bpb-R can, for instance, transduce the chemical input Cu(II) or Hg(II) into the disappearance of its emission, thereby switching the fluorescence measured at the ligand's emission maximum from a high to a low output .…”

Bifunctional Charge Transfer Operated Fluorescent Probes with Acceptor and Donor Receptors. 1. Biphenyl-Type Sensor Molecules with Protonation-Induced Anti-Energy Gap Rule Behavior

“…A number of different systems including, e.g., YES, NOT, AND, OR, NOR, and INHIBIT , logic gates have been reported. At present, the majority of these devices respond to combinations of protons and alkali or alkaline earth metal ions and are ET-operated, i.e., undergo intensity alterations. , Here, however, true ON−OFF or OFF−ON switching, i.e., switching between a nonfluorescent and a highly fluorescent statethough naturally preferredis often not achieved. Examples for CT-operated logic gates that yield spectrally distinguishable species and principally offer different output signals are comparatively rare. , In any case, systems are of interest that display clearly distinguishable changes of different measurable optical parameters specific for certain chemical inputs.…”

Luminescent Excited‐State Intramolecular Proton‐Transfer (ESIPT) Dyes Based on 4‐Alkyne‐Functionalized [2,2′‐Bipyridine]‐3,3′‐diol Dyes

“…The absorption spectrum of T is strongly modified by the presence of Zn II ( Figure 11, top): in particular, the low-energy absorption is significantly redshifted and increased, which is a common consequence of Zn II chelation by terpyridine subunits. [22] Luminescence is also strongly changed (Figure 11, center): it is redshifted and increased according to the stabilization of the terpyridine-based p-p* state. Furthermore, deactivation of some modes promotes radiationless transition in free T. Noteably, both absorption and luminescence changes require one equivalent of zinc triflate to arrive at the end of the process, indicating formation of a 1:1 T/Zn adduct (see Figure 11, bottom).…”