Photochemically induced ATRP was performed with visible light and sunlight in the presence of parts per million (ppm) copper catalysts. Illumination of the reaction mixture yielded polymerization in case of 392 and 450 nm light but not for 631 nm light. Sunlight was also a viable source for the photoinduced ATRP. Control experiments suggest photoreduction of the CuII complex (ligand to metal charge transfer in the excited state), yielding a CuI complex, and a bromine radical that can initiate polymerization. No photoactivation of CuI complex was detected. This implies that the mechanism of ATRP in the presence of light is a hybrid of ICAR and ARGET ATRP. The method was also used to synthesize block copolymers and polymerizations in water.

The rate coefficients for activation (ka0 app) of two alkyl halides, methyl 2-bromopropionate, MBrP, and Brcapped\ud poly(methyl acrylate), by Cu0 were determined under various conditions. The value of ka0 app was studied in two solvents, dimethyl sulfoxide (DMSO) and acetonitrile (MeCN), and their mixtures with methyl acrylate (MA), using tris[2-(dimethylami no)ethyl]amine (Me6TREN) and tris(2-pyridylmethyl)amine (TPMA) as ligands. The experiments showed that the rate of activation increased with the surface area of Cu0 but was typically not affected by the ratio of ligand to initiator, if a sufficient amount of ligand was present. The choice of solvent and presence of monomer/polymer had a small influence on ka0 app. The activation rate coefficient of MBrP was ka0 app= 1.8 × 10−4 cm s−1 with Me6TREN as the ligand in DMSO at 25 °C while the activation rate coefficient of Br-capped poly(methyl acrylate) by Cu0 was slightly lower, ka0 app = 1.0 × 10−4 cm s−1, as measured in a polymerization of MA in MA/DMSO = 1/1 (v/v) with Me6TREN. On the basis of the measured rate coefficients, the activation rate of MBrP by 1 mM CuIBr/Me6TREN (ka1app = 3.2 × 102 M−1 s−1) is similar to the activation rate by 2 km Cu0 wire with diameter of 0.25 mm in 7 mL of DMSO. Thus, under typical conditions, conducted in the presence of ca. 1 cm Cu0 wire, alkyl halides are predominantly activated by CuI species. Consequently, Cu0 acts as a supplemental activator\ud and also as a reducing agent (SARA) because comproportionation dominates disproportionation, for the polymerization of MA in DMSO. These results support the SARA ATRP mechanism rather than the proposed single electron transfer−living radical polymerization (SET-LRP) process, which requires exclusive activation by Cu0 and instantaneous disproportionation of CuI

We report on bidirectional photochemical switching of 6,8-dinitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6,8-dinitro-BIPS) between the ring-closed spiropyran and the ring-open merocyanine form. This is studied by femtosecond three-color pump-repump-probe experiments. Both ring opening and ring closure are photoinduced. Completion of an entire cycle, consisting of opening and subsequent closure, can be achieved within 40 ps. A much shorter time (<6 ps) is needed for the converse cycle, consisting of initial ring closure and subsequent ring opening. Furthermore, we perform pump-probe experiments with ultraviolet/visible pump and visible/mid-infrared probe pulses for an unambiguous spectroscopic identification of the open and closed molecular forms. Following visible excitation of the ring-open molecules, ultrafast ring closure is observed directly in the mid-infrared. The quantum efficiencies for ring opening and ring closure starting from the respective equilibirum states are determined to be approximately 9% and 40%. These results show that 6,8-dinitro-BIPS is an ultrafast bidirectional molecular switch exhibiting a high quantum efficiency.

General:Materials. All chemicals were purchased from commercial sources, e.g., Aldrich, TCI, and used as received if not stated otherwise. Tris(2-pyridylmethyl) amine (TPMA) was purchased from ATRP Solutions. Methyl acrylate (MA) and butyl acrylate (BA) were passed through a column filled with basic alumina to remove inhibitor prior to use. All manipulations for atom transfer radical polymerizations were performed with oxygen free solvents, degassed by at least three Freeze-Pump-Thaw cycles (FPT), using standard Schlenk techniques. Instrumentation.Gel permeation chromatography (GPC): GPC was used to determine number average molecular weight (M n ) and M w /M n values. The GPC was conducted with a Waters 515 HPLC Pump and Waters 2414 Refractive Index Detector using PSS columns (Styrogel 10 2 , 10 3 , 10 5 Å) in tetrahydrofuran (THF) as an eluent at a flow rate of 1 mL/min at 35 o C. The column system was calibrated with 12 linear polystyrene (PSt, M n = 376~2,570,000) and 12 linear poly(methyl methacrylate) (PMMA, M n = 800 ~ 2,570,000) standards. Conversion of monomer was determined by 1 H NMR spectroscopy or gravimetrically. Absolute values of PMA may be calculated utilizing universal calibration as reported in literature. [1] NMR: Monomer conversion was measured using 1 H NMR spectroscopy, using a Bruker Avance 300 MHz or 500 MHz spectrometer at room temperature. For ligand synthesis, NMR spectra were measured using spectrometers at 300 MHz ( 1 H) and 75 MHz ( 13 C). All spectra were recorded in CDCl 3 and chemical shifts (δ) are reported in ppm relative to tetramethylsilane referenced to the residual solvent peaks. [2] Spectra were measured at room temperature unless otherwise stated. MS:Mass spectra were recorded on a mass spectrometer with a Varian Saturn 2100T MS with 3900 GC using an EI source. In each case, characteristic fragments with their relative intensities in percentages are shown. Electrospray mass spectra were measured on a Thermo-Fisher LCQ ESI/APCI Ion Trap containing a quadrupole field ion trap mass spectrometer with electrospray ionization (ESI).CV: All cyclic voltammograms (CV) were measured at 25 o C with a PARC 263A potentiostat.Solutions of CuBr 2 /TPMA* and Cu(OTf) 2 /TPMA* (1.0/1.0 mM) were prepared in dry solvent containing 0.1 M NBu 4 PF 6 as the supporting electrolyte. Measurements were carried out under a N 2 atmosphere at a scanning rate () of 0.1 V s -1 , using a glassy carbon disk and platinum mesh

Atom transfer radical polymerization (ATRP) equilibrium constants (K ATRP) were measured during polymerization of methyl acrylate (MA) with CuIBr/CuIIBr2 in either dimethyl sulfoxide (DMSO) or acetonitrile (MeCN) in the presence of either tris(2-pyridylmethyl)amine (TPMA) or tris[2-(dimethylamino)ethyl]amine (Me6TREN) as the ligand and with ethyl 2-bromopropionate as the initiator. The ln(K ATRP) values changed linearly with the volume fraction of solvents in the reaction medium, allowing extrapolation of the values for K ATRP to bulk conditions, which were 2 × 10–9 and 3 × 10–8 for TPMA and Me6TREN ligands at 25 °C, respectively. The temperature effect on K ATRP values was studied in MA/MeCN = 1/1 (v/v) with TPMA as the ligand in the temperature range from 0 to 60 °C. The K ATRP values increased with temperature providing ΔH = 36 kJ mol–1 in MeCN.