This work describes a fluorescent probe for following changes in the viscosity of the surrounding medium. The optical properties, fluorescence characteristics, and sensitivity to frictional forces with the surrounding medium are superior to the most commonly used molecular probe, namely dicyanovinyl julolidine. The photophysical properties of the target molecule have been recorded in a range of solvents under ambient conditions, over a wide temperature range, and as a function of applied pressure. The mechanism by which the probe responds to changes in local viscosity involves gyration of the mesophenylene ring and accompanying distortion of the dipyrrin framework, as indicated by molecular dynamics simulations. Indeed, temperature-dependence measurements have established that the activation energy is small when the solvent viscosity is relatively low, but there is a turnover to strong activation control at very high viscosity. A small but definite solvent dependence appears when the viscosity is varied by the application of high pressures and this can be traced to differences in the elasticity of the surroundings. Unusually for such fluorescent rotors, there is no indication that the excited state involves charge-transfer interactions. The rotor also responds to changes in the polarizability of the solvent, as induced by changes in applied pressure, and to the extent of polymerization of a monomer. The various experimental observations made at low viscosity are consistent with diffusive motion of the wave packet along the excited-state potential curve until finding a sink that strongly coupled to the highly distorted ground state.

The synthesis is described for a series of five molecular dyads comprising pyrene-based terminals covalently linked through a 1,3-disubstituted phenylene spacer. The extent of through-space communication between the pyrene units is modulated by steric interactions imposed by bulky moieties attached at the 6,8-positions of each pyrene unit. For the control compound, only hydrogen atoms occupy the 6,8 positions (DP1), whereas the remaining compounds incorporate ethynylene groups terminated with either triisopropylsilyl (DP2), 1-tert-butylbenzene (DP3), 2,6-di-tert-butylbenzene (DP4) or 1-tert-butyl-3,5-dimethylbenzene (DP5) units. Each compound shows a mixture of monomer and excimer fluorescence in fluid solution at room temperature, but only monomer emission in a glassy matrix at 77 K. The ratio of monomer to excimer fluorescence depends markedly on the molecular structure; DP1 is heavily biased in favour of the excimer and DP4 is enriched with monomer fluorescence. Photophysical properties, including laser induced and delayed fluorescence data, are reported for each compound. Delayed fluorescence occurs by both intramolecular and bimolecular steps, but these events take place on different timescales. The possibility is raised for using intramolecular triplet-triplet annihilation as a means of molecular imaging.

The first direct use of carbon dioxide in the lactamization of alkenyl and heteroaryl C-H bonds to synthesize important 2-quinolinones and polyheterocycles in moderate to excellent yields is reported. Carbon dioxide, a nontoxic, inexpensive, and readily available greenhouse gas, acts as an ideal carbonyl source. Importantly, this transition-metal-free and redox-neutral process is eco-friendly and desirable for the pharmaceutical industry. Moreover, these reactions feature a broad substrate scope, good functional group tolerance, facile scalability, and easy product derivatization.

Experimental details and spectroscopic data of [(PtThpyCl) 2 L n ], [Pt(Thpy)PPh 3 Cl], and [Pt(Thpy)PPh 3 (CH 3 CN)]ClO 4 , crystallographic data and photophysical spectra. S 2 Experimental Section Materials and General Procedures. [Pt(Thpy)(HThpy)Cl] was prepared by literature method. 1 Acetonitrile for photophysical measurements was distilled over potassium permanganate and calcium hydride. Dichloromethane for photophysical studies was washed with concentrated sulfuric acid, 10 % sodium hydrogen carbonate, and water, dried by calcium chloride, and distilled over calcium hydride. All other solvents were of analytical grade and purified according to conventional methods. 2 p-tert-Butylcalix[4]arene was purchased from Alfa Aesar. Instrumentation and Physical Measurements. Fast atom bombardment (FAB) mass spectra were obtained on a Finnigan Mat 95 mass spectrometer with a 3-nitrobenzyl alcohol matrix, whereas electrospray mass spectra were obtained on a LCQ quadrupole ion trap mass spectrometer. High-resolution ESI mass spectra were obtained from a Waters Micromass Q-Tof Premier quadrupole time-of-flight tandem mass spectrometer. 1 H (500 MHz), 13 C (126 MHz) and 31 P (202 MHz) NMR spectra were performed on DPX 500 Bruker FT-NMR spectrometer with chemical shifts (in ppm) relative to tetramethylsilane ( 1 H and 13 C) and H 3 PO 4 ( 31 P) as references. Elemental analyses were performed by the Institute of Chemistry at the Chinese Academy of Sciences, Beijing. UV-vis spectra were recorded on a Perkin Elmer Lambda 19 UV/vis spectrophotometer. Emission and Lifetime Measurements. Steady-state emission spectra were recorded on a Fluorolog-3 Model FL3-21 spectrophotometer. Solution samples for measurements were S 3degassed with at least four freeze-pump-thaw cycles. Low-temperature (77 K) emission spectra for glassy solutions and solid-state samples were recorded in 5 mm diameter quartz tubes, which were placed in a liquid nitrogen Dewar equipped with quartz windows. The emission spectra were corrected for monochromator and photomultiplier efficiency and for xenon lamp stability. Emission lifetime measurements were performed with a Quanta Ray DCR-3 pulsed Nd:YAG laser system (pulse output 355 nm, 8 ns). The emission signals were detected by a Hamamatsu R928 photomultiplier tube and recorded on a Tektronix TDS 350 oscilloscope. Errors for λ values (± 1 nm), τ (± 10 %), Φ (± 10 %) were estimated.Luminescence quantum yields were determined using the method of Demas and Crosby 3 with [Ru(bpy) 3 ]Cl 2 in degassed acetonitrile as a standard reference solution (Φ r = 0.062) and calculated according to the following equation: Φ s = Φ r (B r /B s )(n s /n r ) 2 (D s /D r ), where the subscripts s and r refer to sample and reference standard solution respectively, n is the refractive index of the solvents, D is the integrated intensity, and Φ is the luminescence quantum yield. The quantity B was calculated by B = 1 − 10 −AL , where A is the absorbance at the excitation wavelength and L is the optical path length. . 5,26,27,arene ...