Abstract
Two new pyrrolylquinoline-substituted heteroaromatic-containing compounds bearing a central boron bridge have been prepared by a short, high-yielding sequence consisting of Suzuki-coupling of 8-bromoquinoline and N-Boc 2-pyrroleboronic acid, thermolytic tert-butyloxycarbonyl deprotection, and subsequent boron chelation (either using boron trifluoride or triphenylborane). Both derivatives display longer wavelength absorption maxima (λabsmax) than a previously reported indolopyridine-BPh2 analogue, in agreement with the smaller HOMO-LUMO energy gap predicted by DFT quantum chemical calculations. Both of the pyrrolylquinoline-boron chelates display weak emission (quantum yields 0.3–0.9%) and the BPh2 complex displays a very broad, long-wavelength emission (λemmax = 715 nm, MeCN), which may be due to dimer emission and results in a large pseudo-Stokes’ shift (7753 cm−1) for this compound.
Highlights
Since the initial report by Treibs and Kreuzer, who detailed the first examples of BODIPY derivatives [1], the field of chemistry associated with developing new fluorescent materials involving π-conjugated systems has drawn considerable attention across scientific boundaries [2,3,4,5,6]
The need for developing new fluorescent molecules is supported by the growing number of applications that they can be found in, for example, as metal or ion sensors [7,8,9,10], dyes used in laser spectroscopy [11,12,13,14,15], photo-labels in biological studies [16,17,18,19,20], incorporated into polymers [21,22], molecular rotors [23,24], amongst others
To confirm the structure of BF2 -chelated pyrrolylquinoline compound 8, we initially investigated multi-nuclear NMR analysis for this product
Summary
Since the initial report by Treibs and Kreuzer, who detailed the first examples of BODIPY derivatives [1], the field of chemistry associated with developing new fluorescent materials involving π-conjugated systems has drawn considerable attention across scientific boundaries [2,3,4,5,6]. The fusion of quinoline derived units with either indoles [35], pyridines [36] and imidazoles [37], and subsequently formed as boron(III) complexes, has been reported in the literature (and their fluorescent properties studied). These findings built on the seminal work dating back to the late sixties, in which Hohaus reported the first quinoline-boron(III) complexes that
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