Synthesis, Photophysical and Electrochemical Properties, and Protein‐Binding Studies of Luminescent Cyclometalated Iridium(III) Bipyridine Estradiol Conjugates

Abstract

A new series of luminescent cyclometalated iridium(III) bipyridine estradiol conjugates [Ir(N-C)2(N-N)](PF6) (N-N = 5-(4-(17alpha-ethynylestradiolyl)phenyl)-2,2'-bipyridine, bpy-est, HN-C = 2-phenylpyridine, Hppy (1 a), 1-phenylpyrazole, Hppz (2 a), 7,8-benzoquinoline, Hbzq (3 a), 2-phenylquinoline, Hpq (4 a), 2-((1,1'-biphenyl)-4-yl)benzothiazole, Hbsb (5 a); N-N = 4-(N-(6-(4-(17alpha-ethynylestradiolyl)benzoylamino)hexyl)aminocarbonyl)-4'-methyl-2,2'-bipyridine, bpy-C6-est, HN-C = Hppy (1 b), Hppz (2 b), Hbzq (3 b), Hpq (4 b), Hbsb (5 b)) was synthesized, characterized, and their photophysical and electrochemical properties studied. Upon photoexcitation, all the complexes displayed intense and long-lived emission in fluid solutions at 298 K and in low-temperature glass. The emission of complexes 1 a-3 a and 1 b-3 b was assigned to a triplet metal-to-ligand charge-transfer ((3)MLCT) (dpi(Ir)-->pi*(bpy-est and N-C-)) state mixed with some triplet intraligand ((3)IL) (pi-->pi*) (N-C- and N-N) character. However, the emissive states of the pq- and bsb- complexes 4 a, 4 b, 5 a, and 5 b showed substantial (3)IL (pi-->pi*) (pq-/bsb-) character. The lipophilicity of all the complexes was determined by reversed-phase HPLC. Upon binding to estrogen receptor alpha, all of these iridium(III) estradiol conjugates exhibited emission enhancement and lifetime extension, rendering them a novel series of luminescent probes for this receptor.

Chromo- and Fluorogenic Organometallic Sensors

“…14) [149] and the related Ir(III) complexes (15d and 15e, Fig. 15) [150], demonstrate lifetime extension and enhanced fluorescence in the presence of oestrogen receptor a. In a related study, a cyclometallated Pt(II) complex (16, Fig.…”

Exploitation of Luminescent Organometallic Rhenium(I) and Iridium(III) Complexes in Biological Studies

“…Upon binding of the biotin unit to avidin, the donor and acceptor are forced closer to each other by the protein matrix, leading to more efficient energy transfer from the donor to the emitting iridium complex and thus a higher emission intensity (I/I o = 14). + (N^C = ppy, ppz, bzq, pq, bsb) (39) has been designed [80]. As expected, all the complexes display intense and longlived 3 MLCT (dp(Ir) → p*(N^N and N^C))/ 3 IL (p → p*) (N^N and N^C) emission in fluid solutions at 298 K and in low-temperature glass.…”

Metallodrug Conjugates with Steroids and Selective Estrogen Receptor Modulators (SERM)

“…As verified by flow cytometry and live-cell confocal imaging studies conjugates 21 were readily internalized by the HeLa cells and maintained their emission after the uptake [61]. Earlier, the same group had prepared similar luminescent iridium(III) bipyridine estradiol conjugate complexes [62].…”