ABSTRACT
A new series of Oâ§C-chelate tetra-coordinated boranes with naphtha-aldehyde as the chelate backbone have been synthesized. Their photophysical and photochemical properties have been examined, which show that all of the compounds can undergo both photo and thermal transformations, generating aryl-migrated [1,2]oxaborinine derivatives as the major products. 1,3-Sigmatropic shifts and an intramolecular nucleophilic addition mechanism are proposed for the photochemical and thermal conversion pathways, respectively.
ABSTRACT
Boron compounds (1-4) containing an internal B-O bond have been found to undergo facile multistructural transformations upon irradiation at 365 or 410 nm, generating rare 8-membered B,O-heterocycles (1c-4c). In addition, 2 and 3 also undergo an intramolecular Diels-Alder addition and oxyborane elimination concomitantly, via intermediates 2b/3b, producing 2d/3d. The pathways to isomer c and product d were found to be a thermal process and a photo process, respectively.
ABSTRACT
The key intermediate, 4a,4b-dihydrophenanthrene (DPH), involved in the photocyclization of stilbene and derivatives is known to be unstable, and is therefore poorly characterized/understood. We have found that functionalising stilbenes with NMe2 and BMes2 groups can greatly enhance the stability of 4a,4b-DPHs, allowing quantitative isolation and full characterization of these rare species. Furthermore, we discovered that the new amino-borane decorated 4a,4b-DPHs can undergo thermal [1,5] H sigmatropic shift, forming isomers 4a,10a-DPHs. Both 4a,4b-DHPs and 4a,10a-DHPs are stable towards air and moisture, while only the former were found to undergo oxidative dehydrogenation upon irradiation at 365 nm under air, yielding brightly blue/green fluorescent NMe2 and BMes2 functionalised phenanthrene analogues. Control studies established that the trans-Mes2B-Ph-NMe2 unit is responsible for the stability of these isolated 4a,4b-DHPs and their [1,5]-H shift isomers.
ABSTRACT
A simple aldehyde functionalized amino-triarylborane donor-acceptor system (BO-1) was found to display distinct responses toward multiple external stimuli including solvent, temperature and pressure, with emission colours changing from blue to red. The operating mechanism most likely involves reversible switching between closed and open structures based on an intramolecular B â O bond. Imbedded donor-acceptor charge transfer transitions played a key role in the multi-coloured fluorescent response of this new boron system to external stimuli. Multi-coloured and erasable fluorescent images on solid substrates based BO-1's "turn-on" response toward solvents, particularly water, are demonstrated.
ABSTRACT
A new europium complex coordinated between a Eu(III) ion and an unsymmetrical diarylperfluorocyclopentene yields a light-controlled diarylethene-europium dyad, DAE@TpyEu(tta)3, whose photophysical properties can be reversibly switched by optical stimuli. When DAE@TpyEu(tta)3 is exposed to 365 nm UV light, an efficient intramolecular photochromic fluorescence resonance energy transfer (pc-FRET) occurs between the emission of the Eu(3+) donor (D) and the absorption of the diarylethene acceptor (A) in closed-form DAE@TpyEu(tta)3 accompanied by luminescence quenching. However, the pc-FRET process could be effectively inhibited by visible light (λ > 600 nm) irradiation, and the lanthanide emission of DAE@TpyEu(tta)3 is rapidly recovered. Furthermore, this luminescent lanthanide molecular switch could serve as a highly reliable and sensitive "turn on" fluorescent marker in living cells irradiated by red light without any optical interference.
