We report on the first experimental and theoretical investigations of ultrafast intramolecular energy transfer for a novel class of highly luminescent materials - nanostructured organosilicon ...luminophores (NOLs). For this purpose we designed, synthesized and investigated a NOL,
(POPOP)Si
2
(3Ph-EH)
6
, consisting of six
p
-terphenyl (
3Ph
) donor and 1,4-bis(5-phenyloxazol-2-yl)benzene (
POPOP
) acceptor luminophores - well-known laser dyes widely used in plastic scintillators as an activator and a spectral shifter, respectively. The NOL shows excellent optical properties - molar absorption coefficient up to 2.6 × 10
5
L mol
−1
cm
−1
, photoluminescence quantum yield up to 96% and pseudo Stokes shift of 100 nm. Its intramolecular energy transfer efficiency determined from steady-state optical measurements was found to be 93%, while the excitation lifetime was less than 1 ns. For deeper understanding of the processes of intramolecular energy transfer within NOLs, ultrafast spectroscopy investigations of the NOL, model donor and acceptor luminophores were performed for the first time for this class of compounds. It was found that the time constant of the energy transfer from donor to acceptor luminophores within the NOL is
τ
1
= 105 fs, which is significantly faster than the vibrational relaxation within the donor (
ca.
400 fs). Based on these findings, a kinetic scheme of the electronic excitation energy deactivation processes in the NOL was developed. The results obtained not only directly prove that the mechanism of energy transfer within the NOLs is based on Förster resonance energy transfer of the excitation energy from donor to acceptor luminophores, but also highlight the advantages of NOLs and NOL-based materials for future photonics applications - fast and efficient plastic scintillators, scintillating fibers and other spectral shifting optical materials.
Förster theory allows quantitative description of the ultrafast intramolecular energy transfer observed experimentally within nanostructured organosilicon luminophores (NOLs).
Abstract
Endocrine hormone function has been shown to regulate numerous oncogenic processes from tumor progression, promotion, and dependence to prevention, diagnosis, and treatment. Notably, ...estrogen and androgen activity in breast and prostate cancers have been used to diagnose steroid hormone dependence and determine therapy options. Endocrine disruptors are compounds that mimic estrogen or androgen steroid activity and affect the endocrine system by altering hormone function, providing possible therapies for endocrine-dependent cancers. Screening complex chemical libraries for endocrine disruptors and investigating the molecular and cellular effects of existing treatment strategies is accelerated by using high throughput procedures to assess endocrine activity and potential cancer therapeutic efficacy.
Redistribution® technology can be used to monitor the localization of GFP-tagged proteins in response to extra-cellular stimuli such as treatment with steroid compounds or activation of signaling cascades. Redistribution® GFP-tagged steroid receptors such as estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and androgen receptor (AR) form nuclear foci in response to hormone stimulation that can be easily monitored and quantitated by automated image analysis, thereby establishing a high-throughput screen for both agonists and antagonists of ER and AR activation. Additionally, multiplexed cell and nuclear phenotypes such as receptor kinetics, cellular health, and cell cycle effects can be monitored simultaneously following direct or indirect receptor stimulation.
Here we utilize Redistribution® cell lines and known endocrine agonist and antagonists to establish a screen for ER and AR disruptors. For ER screens, cells were treated with agonists including 17β-estradiol and bisphenol A with and without antagonists such as fulvestrant (ICI 182,780) and tamoxifen. AR cells were treated with dihydrotesterone (5α-androstan-17β-ol-3-one) or progesterone agonists in the presence or absence of the AR antagonist mifepristone (RU 486). Following fixation and Hoechst staining, plates were analyzed using a quantitative automated imaging platform to evaluate features such as nuclear translocation (for AR only), nuclear GFP foci count, area, and intensity, and overall nuclear morphology on a cell-by-cell basis. EC50 values were determined from dose-dependent response curves of the treatments to establish hierarchical receptor activation comparisons for both ER and AR. Z-factors for these features indicate that using this technology gives a robust assay with high reproducibility. This data suggests that ER and AR Redistribution® cell lines can be effectively utilized with high throughput automated image analysis to screen for potential steroid hormone agonists and antagonists that would increase cancer therapeutic efficacy and specificity.
Citation Format: {Authors}. {Abstract title} abstract. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4882. doi:10.1158/1538-7445.AM2011-4882
Synthesis and investigation of optical and thermal properties of a homologous series of highly luminescent nanostructured organosilicon luminophores (NOLs) containing different donor to acceptor ...ratio (D:A) are reported. Each of the NOL consists of a 1,4-bis(5-phenylthienyl-2-yl)benzene (PTPTP) acceptor unit and four, six or twelve 2,2′-bithienyl donor fragments connected to each other through two or six silicon atoms. These complex molecules show a “molecular antenna” effect with high efficiency of intramolecular energy transfer about 97-98% combined with excellent photoluminescence (PL) quantum yield of 84-91% and fast PL decay time of 0.90-0.95 ns. A significant increase of the molar extinction coefficient from 94 000 to 257 000 M
cm
with increasing the D:A ratio from 4:1 to 12:1 was observed. It was found that increasing the branching extent in the NOLs prohibits their crystallization. Thermal gravimetric analysis (TGA) showed that all the NOLs reported, regardless of their branching extent, are thermally stable up to 455 °C under nitrogen. These characteristics make them promising materials for various organic photonics applications.
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