Stimuli Responsive Furan and Thiophene Substituted Difluoroboron ß-Diketonate Materials.

Difluoroboron ß-diketonate (BF2bdk) compounds exhibit solid-state switchable luminescence under excitation by UV light. This property is usually manifested as a blue-shift in emission when dye films are thermally annealed followed by a red-shift in response to mechanical shear (i.e. mechanochromic luminescence). Here we report thiophene and furan heterocycle-substituted dyes bearing short methoxy and long dodecyloxy chain substituents. Optical properties of the dyes were investigated in solution, pristine powders, and films on paper and glass. The structural and thermal properties of the dyes were also investigated by powder x-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The methoxy-substituted dyes exhibited neither thermal nor mechano-responsive behavior, however, addition of a longer C12 alkoxyl chain substituent resulted in stimuli-responsive behavior. The furan and thiophene dodecyloxy-substituted dyes both exhibit high-contrast reversible luminescence switching between crystalline, blue-shifted and amorphous red-shifted emissive states. For the furan dye, gentle heating produced a green emissive form while melting followed by rapid cooling produced an orange emissive form. The thiophene dye, on the other hand, exhibited blue-shifted emission when annealed below its melting temperature and red-shifted emission when smeared with a cotton swab (mechanochromic luminescence). These transformations for both dyes were found to be completely reversible, making them potential candidates for applications requiring reusable, functional materials.

Oxygen-Sensing Difluoroboron Thienyl Phenyl ß-Diketonate Polylactides.

Difluoroboron ß-diketonate-polylactides are versatile oxygen-sensing materials. These materials have both fluorescence (F) and oxygen-sensitive, room-temperature phosphorescence (RTP). The fluorescence, being insensitive to oxygen, can act as an internal standard to the changing phosphorescence, and ratiometric sensing of oxygen can be achieved with these simple, single-component materials. To expand the range of colors for this family of fluorophores, a series of thienyl-phenyl-substituted dyes were synthesized with initiator sites for the ring-opening polymerization of lactide. Heavy atoms (Br and I) were added to the dye to modulate the phosphorescence intensity. These halide-substituted thiophene dyes readily aggregated in the poly(lactic acid) (PLA) matrix, generating two fluorescence peaks in air, one for monomer emission and another for aggregate emission. When the dye was dilute in PLA, as a blend, the iodo-thienyl derivative showed impressive singlet-triplet splitting, with blue fluorescence (440 nm) and orange phosphorescence (585 nm), the largest gap recorded for a boron ß-diketonate dye. Nanoparticles fabricated from a mixture of PLA and dye-PLA conjugated polymer benefited from the large singlet-triplet splitting to yield oxygen sensitivity at levels between 0 and 21 %, which can be utilized in biological oxygen-sensing applications.

Thienyl Difluoroboron ß-Diketonates in Solution and Polylactide Media.

Difluoroboron ß-diketonates have impressive optical properties in both solution and the solid state. In particular, both fluorescence and room-temperature phosphorescence are present when the dyes are confined to a rigid matrix, such as poly(lactic acid) (PLA). To expand current knowledge and color range capabilities of this unique type of multi-emitting chromophore, a series of thienyl-substituted BF2bdk complexes have been synthesized. The photophysical properties were investigated in methylene chloride solution and in the solid state as dye/PLA blends. By varying donor ability, i.e. methyl, phenyl, methoxyl, and thienyl substituents, and by changing the dye loading in the PLA media (0.1-10% dye loading) red-shifted emission was achieved, important for biological imaging applications. In dilute CH2Cl2 solution, complexes exhibited absorptions ranging from 350 - 420 nm, solid-state fluorescence in PLA ranging from 390 - 500 nm, and oxygen sensitive phosphorescence ranging from 540 - 585 nm in PLA blends. Promising candidates as dye/PLA blends serve as models for dyepolymer conjugates for application as biological oxygen nanoprobes.

Mechanochromic Luminescence and Aggregation Induced Emission of Dinaphthoylmethane ß-Diketones and Their Boronated Counterparts.

Mechanochromic luminescence has been observed in many boron coordinated ß-diketonate (BF2bdk) complexes. Recently, it was shown that the metal-free methoxy-substituted dinaphthoylmethane ß-diketone (dnmOMe) also displayed aggregation induced emission (AIE), solvatochromism, and high contrast mechanochromic luminescence (ML) that recovered rapidly at room temperature. In order to understand how substituents and boron coordination affect solution and solid-state optical properties, a series of methoxy- and bromo-substituted derivatives (dnm, dnmOMe, dnmBr, and dnmBrOMe) and their corresponding boron complexes (BF2dnm, BF2dnmOMe, BF2dnmBr, and BF2dnmBrOMe) were synthesized and their AIE, ML, and room temperature recovery properties were compared. All boron complexes exhibited red-shifted absorption and emission, in addition to larger solution and solid-state quantum yields than ß-diketones. While AIE studies show increased emission for dnmOMe and dnmBrOMe, the emission of corresponding boron complexes diminished upon aggregation. However, boron complexes were still strongly emissive in the solid state. ML properties were investigated using spin-cast films. Smearing resulted in the appearance of blue-green emission in ligands and a color change from green to yellow-orange in boron complexes. Bromide substituted derivatives showed increased room temperature recovery times compared to other dnm ligands, and boron complexes show only partial recovery over several days.

Blue Thermally Activated Delayed Fluorescence from a Biphenyl Difluoroboron ß-Diketonate.

Optical properties of biphenyl difluoroboron ß-diketonates were studied in poly(lactic acid) (PLA) blends. Increased conjugation lowered the emission energy, decreased the singlet-triplet energy gap and yielded blue thermally activated delayed fluorescence (TADF). The properties of these biphenyl dyes may inform organic light emitting diode (OLED) and bioimaging agent design.

Mechanochromic luminescence and aggregation induced emission for a metal-free ß-diketone.

Reversible mechanochromic luminescence (ML) is known for difluoroboron ß-diketonates (BF2bdks). Here, we report ML for the methoxy-substituted dinaphthoylmethane (dnmOMe) ligand even without coordination to boron. In addition, dnmOMe shows solvatochromism and aggregation-induced emission (AIE). Diketone thin films showed high contrast emission when smeared, and rapid recovery of the pre-smeared state at room temperature.

Dual-Emissive Difluoroboron Naphthyl-Phenyl ß-Diketonate Polylactide Materials: Effects of Heavy Atom Placement and Polymer Molecular Weight.

Luminescent materials are important for imaging and sensing. Aromatic difluoroboron ß-diketonate complexes (BF2bdks) are classic fluorescent molecules that have been explored as photochemical reagents, two-photon dyes, and oxygen sensors. A series of BF2bdks with naphthyl and phenyl groups was synthesized, and photophysical properties were investigated in both methylene chloride and poly(lactic acid) (PLA). Polymer molecular weight and dye attachment site along with bromide heavy atom placement were varied to tune optical properties of dye-PLA materials. Systems without heavy atoms have long phosphorescence lifetimes, which is useful for lifetime-based oxygen sensing. Bromine substitution on the naphthyl ring resulted in intense, clearly distinguishable fluorescence and phosphorescence peaks important for ratiometric oxygen sensing and imaging.

Association between p53 and human papillomavirus in head and neck cancer survival.

BACKGROUND: High-risk human papillomavirus (HPV-HR) is a significant risk factor for head and neck cancer (HNC), abrogating normal p53 function. In addition, HPV and p53 have been associated with prognosis of these tumors but the findings have been inconsistent. We examined p53 expression and HPV-HR individually and jointly for differences in predicting HNC survival. METHODS: HNC patients (n = 294) were evaluated for p53 by immunohistochemical staining. HPV was detected by PCR/dot blot hybridization and sequencing. RESULTS: HNC tumors showed 48% with p53 overexpression and 27% with HPV-HR. Multivariate analyses showed that p53 positivity was significantly associated with higher risk of disease-specific [hazard ratio (HR); 2.0; 95% confidence interval (95% CI), 1.1-3.7] and recurrence-free mortality (HR, 2.8; 95% CI, 1.4-5.3). HPV- cases had significantly worse disease-specific survival (HR, 2.8; 95% CI, 1.3-6.3) compared with HPV-HR cases. When analyzed jointly, with p53(-)/HPV-HR tumors as the reference group, p53(+)/HPV(-) patients had the worst disease-specific (HR, 5.3; 58% versus 15%, P = 0.006) and recurrence-free survival rates (HR, 9.5; 17% versus 89%, P = 0.001), in contrast to the p53(-)/HPV(-) and p53(+)/HPV-HR groups, which had less elevated and different risks for disease-specific survival (HR, 2.5 and 1.7, respectively) and recurrence-free survival (HR, 4.2 and 7.2, respectively). CONCLUSION: Joint assessment of p53/HPV status provides different HRs for each clinical outcome in the four biomarker groups that are distinct from the individual biomarkers. These findings suggest that joint assessment of p53/HPV provides a better indicator of prognosis and potentially different types of treatments.