Red/Near-Infrared Luminescence Tuning of Group-14 Element Complexes of Dipyrrins Based on a Central Atom

Abstract

A dipyrrin complex has been one of the most utilized fluorescent dyes, and a variety of dipyrrin complexes show intriguing functions based on the various coordination structures of the central element. We now report the synthesis, structure, and photophysical properties of germanium and stannane complexes of the N2O2-type tetradentate dipyrrin, L·Ge and L·Sn, which are heavier analogues of the previously reported dipyrrin silicon complex, L·Si. The central group-14 atoms of the monomeric complexes have geometries close to trigonal bipyramidal (TBP), in which the contribution of the square-pyramidal (SP) character becomes higher as the central atom is heavier. Interestingly, L·Sn formed a dimeric structure in the crystal. All complexes L·Si, L·Ge, and L·Sn showed a fluorescence in the red/NIR region. Fluorescence quantum yields of L·Ge and L·Sn are higher than that of L·Si. These results indicated that the central atom on the dipyrrin complexes contributes not only to the geometry difference but also to tuning the fluorescence properties.

Luminescent Silk Fibroin with Organotin Compounds from Amino Acid Schiff Bases – Microwave‐Assisted Synthesis, Chemo‐Optical Characterization, Cytotoxicity, and Confocal Microscopy

“…This distorted geometry is also observed in the axial plane defined by the O(1)–Sn–O(2) angle, the value of which is very close to 160° (Table ). On the other hand, the N(1)–Sn bond lengths are in accordance with the values reported previously for coordinative bonds in pentacoordinate tin‐containing dibutyl fragments , . Compound 1 has intermolecular hydrogen‐bond interactions (Figure ) between the oxygen atom from the ester fragment and the hydrogen atom of the indole group from tryptophan with a bond length of 2.076 Å and a N2–H ··· O1 angle of 169.49°.…”

“…Moreover, all of the complexes show three doublets of doublets in the range δ = 2.65 to 4.46 ppm, assigned to the chiral proton 13‐H [ δ ≈ 4.3 ppm, 3 J ( 1 H, 1 H) ≈ 3, 10 Hz] and the diastereotopic protons of the methylene group C‐14 [ δ ≈ 3.5 and 2.9 ppm, 2 J ( 1 H, 1 H) ≈ 3, 14 and 9, 14 Hz, respectively]. All of these values agree with the values reported for the diphenyl and dibutyltin complexes of a series of Schiff bases obtained previously , , . Thus, the NMR data confirm the presence of N→Sn coordination in all of the complexes.…”

“…Another appealing property of organotin compounds derived from Schiff bass complexes is that they can act as analytical fluorescent chemosensors for the identification of metals in live cells by confocal microscopy. A comparison between the group 14 elements (Si, Ge, and Sn) revealed that Sn atoms improve the quantum yields of dipyrrins through the heavy‐atom effect . Recently, fluorescent organotin compounds derived from Schiff bases were utilized for the fabrication of organic light‐emitting diodes (OLEDs) and as cytoplasmic dyes, which were practically innocuous to murine skin melanoma B16F10 cells at 0.1 µg mL –1…”

Design and Synthesis of Dipyrrin Complexes Bearing Unique Structures, Properties and Functions

“…The germanium and tin complexes 8 and 9 were synthesized in a similar way (Table 1, entries 5 and 6). 10 X ray crystallographic analysis of 8 revealed that the germanium center adopted a trigonal bipyramidal (TBP) geometry similar to the silicon complex 7c but the geometry of 8 (τ 0.67) is more distorted from the ideal TBP structure than that of 7c (τ 0.82). In contrast, the tin complex 9 adopts a dimeric hexacoordinate structure.…”

“…The association constant (K a ) was determined by spectral titration to be (7.3 2.3) 10 7 M 1 . The large value of K a is indicative of the negligible dissociation process of the complex.…”