Systematic Studies on Photoluminescence of Oligo(arylene‐ethynylene)s: Tunability of Excited States and Derivatization as Luminescent Labeling Probes for Proteins

Abstract

Functionalized oligo(phenylene‐ethynylene)s (OPEs) with different conjugation lengths, p‐X(C6H4C≡C)nSiMe3 (n = 1–4; X = NH2, NMe2, H) were synthesized by Sonogashira coupling of (phenylene‐ethynylene)s and 1‐iodo‐4‐(trimethylsilylethynyl)benzene, followed by desilylation of the p‐substituted (trimethylsilylethynyl)benzenes with potassium hydroxide. The photoluminescent properties for the OPE series with different chain lengths and their solvatochromic responses were examined. The absorption maxima were red‐shifted with increasing numbers of –(C6H4C≡C)– units (n), and a linear plot of the absorption energy maxima vs. 1/n was obtained for each series. The emission spectra in dichloromethane showed a broad and structureless band, the energies of which (in wavenumbers) also fit linearly with 1/n. Both the absorption and emission wavelength maxima of the NH2‐ and NMe2‐substituted OPEs exhibited significant solvent dependence, whereas the parent OPEs (X = H) showed only minor shifts of the λmax values in different solvents. Substituent effects upon the photoluminescent characteristics of the OPEs and the tunability of the excited states were examined with the p‐X(C6H4C≡C)nSiMe3 (n = 2, 3; X = NH2, NMe2, H, SMe, OMe, OH, and F) series. The H‐ and F‐substituted counterparts exhibited high‐energy vibronically structured emissions attributed to the 3(ππ*) excited states of the (arylene‐ethynylene) backbone. For compounds bearing NH2 and NMe2 groups, a broad red‐shifted emission with a remarkable Stokes shift from the respective absorption maximum was observed, which can be assigned to an n → π* transition. The n → π* assignment was supported by MO calculations on the model compounds p‐X(C6H4C≡C)2SiH3 (X = NH2, H). Functionalization of the oligo(arylene‐ethynylene)s with the N‐hydroxysuccinimidyl (NHS) moiety enabled covalent attachment of the fluorophore to HSA protein molecules. A series of fluorescent labels, namely p‐X(C6H4C≡C)nC6H4NHS, (n = 1, X = NH2, NMe2, SMe, OMe, OH, F; n = 2, X = NH2, NMe2) and p‐Me2NC6H4C≡C(C4H2S)C≡CC6H4NHS were synthesized, and their conjugates with HSA (human serum albumin) were characterized by MALDI‐TOF mass spectrometry, UV/Vis absorption spectroscopy, and gel electrophoresis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Ligand‐to‐Ligand Charge‐Transfer Transitions of Platinum(II) Complexes with Arylacetylide Ligands with Different Chain Lengths: Spectroscopic Characterization, Effect of Molecular Conformations, and Density Functional Theory Calculations

“…Cross-coupling reactions [9] of [Pt- 12] with HC CR [11] in the presence of a catalytic amount of CuI and diisopropylamine in CH 2 Cl 2 or a mixture of CH 2 Cl 2 /CH 3 CN (Me = methyl) gave complexes 1-22 with product yields ranging from 56 to 90 %.…”

“…General: [PtA C H T U N G T R E N N U N G (tBu 3 tpy)Cl]ClO 4 [10] and acetylenes [11] were prepared according to literature methods. (Caution: perchlorate salts are potentially explosive and should be handled with care and in small amounts.)…”

Gold‐ and Silver‐Catalyzed Reactions of Propargylic Alcohols in the Presence of Protic Additives

“…1 1 a 2 a 91 12 1 l 2 l 78 (18:1) 83 [b] , and there was no evidence for the Au-catalyzed reaction of the electron-rich heterocycle with the pendant enone in the product. [17] Further combinations of substituents could also be incorporated ( Table 1, entries [18][19][20][21][22] including cyclopropanes (1 r and 1 v), which did not undergo ring-opening during the rearrangement reaction. The dienone 2 v ( Table 1, entry 22) can be generated in excellent yield from the corresponding propargylic alcohol 1 v. Interestingly the initial major product observed from the rearrangement was the E,E isomer.…”

Oligo(p‐phenylene ethynylene)–BODIPY Derivatives: Synthesis, Energy Transfer, and Quantum‐Chemical Calculations

“…They are also attractive functional building blocks for the construction of new molecular and supramolecular photoactive devices. Thus, OPEs have been widely applied in organic electroluminescent lightemitting devices, [12] molecular electronic switches, [13] and nonlinear optical materials. [14] Herein we report the preparation and energy-transfer properties of oligo(p-phenylene ethynylene)-BODIPY (OPEB) cassettes in which a series of OPEs with different conjugated chain lengths are capped at both ends with BODIPY chromophores.…”