Phosphorus Complexes of meso-Triaryl-25-oxasmaragdyrins

Abstract

The aromatic PO2 complexes of meso-triaryl-25-oxasmaragdyrins were synthesized by treating the free base 25-oxasmaragdyrins with POCl3 in toluene/triethylamine at refluxing temperature. The complexes are stable and characterized by X-ray and different spectroscopic techniques. In these complexes, the phosphorus(V) ion was bound to two pyrrolic nitrogen atoms of the smaragdyrin macrocycle and two oxygen atoms in tetrahedral geometry. The X-ray structure revealed that the smaragdyrin macrocycle showed significant distortion upon insertion of a PO2 unit, and the phosphorus atom lies 1.339 Å above the mean plane defined by three meso-carbon atoms of the macrocycle. These complexes absorb strongly in the visible region and are 2.5 times more strongly fluorescent than free base 25-oxasmaragdyrins. The smaragdyrin macrocycle becomes electron-deficient upon complexation with a PO2 unit because these complexes are easier to reduce but difficult to oxidize compared to free base smaragdyrins. We designed and synthesized a covalently linked BODIPY-PO2-smaragdyrin dyad and demonstrated efficient energy transfer from the BODIPY unit to the PO2-smaragdyrin unit.

Strongly Coupled Oxasmaragdyrin–BF2 Chelated Dipyrrin Dyads: Syntheses, X‐ray Structure, Ground‐ and Excited‐State Charge‐Transfer Interactions

“…Long-lived charge-separated states have been obtained by am ulti-modular approach in which sequential electron transfer leadingt os patially distantc ation and anion radical ions has been the common approach. [49] Thus,s uch chelated oxasmaragdyrins provide ag reat opportunity to build donor-acceptor systems to investigatel ight-induced electronand energy-transfer events. [39][40][41][42][43][44][45][46] Some of these hetero-macrocyclic compounds are known for their strong absorption and emission, and useful redox properties, thus making them useful materials for buildingl ight-energy-harvestings ystems.…”

Mixed Boron(III) and Phosphorous(V) Complexes of meso‐Triaryl 25‐Oxasmaragdyrins

“…Upon complexation with the BF 2 or PO 2 unit, the smaragdyrin macrocycle displayed enhanced stabilityw ith significantly altered features in the absorption and emission spectra. [7,8] We also demonstratedt hat BF 2 -oxasmaragdyrins 3 can participate in energy transfer by covalently linking the BF 2 -smaragdyrin macrocycle with energy-donating fluorophores (e.g.,b oron dipyrromethenes and porphyrins). [9][10][11][12] As mentioned above,t he BF 2 /PO 2 units in both oxasmaragdyrin complexes 3 and 4 wereo nly bound to the dipyrrin moiety,b ut the tripyrrin moiety of the smaragdyrin that containst wo donor pyrrole nitrogen atoms ando ne furan oxygen atom remained uncoordinated in these molecules.…”

“…Moreover, 25‐oxasmaragdyrins have also been shown to form both metal and non‐metal complexes . In particular, we recently demonstrated that the 25‐oxasmaragdyrins form highly fluorescent complexes with BF 2 and PO 2 ( 3 and 4 , respectively; Scheme ) bound via the two pyrrole nitrogen atoms of the dipyrrin moiety of the 25‐oxasmaragdyrin macrocycle. Upon complexation with the BF 2 or PO 2 unit, the smaragdyrin macrocycle displayed enhanced stability with significantly altered features in the absorption and emission spectra .…”

“…In particular, we recently demonstrated that the 25‐oxasmaragdyrins form highly fluorescent complexes with BF 2 and PO 2 ( 3 and 4 , respectively; Scheme ) bound via the two pyrrole nitrogen atoms of the dipyrrin moiety of the 25‐oxasmaragdyrin macrocycle. Upon complexation with the BF 2 or PO 2 unit, the smaragdyrin macrocycle displayed enhanced stability with significantly altered features in the absorption and emission spectra . We also demonstrated that BF 2 –oxasmaragdyrins 3 can participate in energy transfer by covalently linking the BF 2 –smaragdyrin macrocycle with energy‐donating fluorophores (e.g., boron dipyrromethenes and porphyrins) .…”

N-methylated 25-oxasmaragdyrins: Synthesis, structure and properties

“…The 25-oxasmaragdyrins exhibit very interesting spectral and electrochemical properties. The electronic properties of the 25-oxasmaragdyrins can be altered significantly by complexing it with BF 2 and PO 2 moieties (Chart 1) to prepare BF 2 -25-oxasmaragdyrin 3 [5] and PO 2 -25-oxasmaragdyrin 4 [6]. The BF 2 3 and PO 2 4 complexes of 25-oxasmaragdyrins are very stable and absorb and emit in the Vis-NIR region with decent quantum yields.…”