Triplet-triplet annihilation (TTA) based upconversions are attractive as a result of their readily tunable excitation/emission wavelength, low excitation power density, and high upconversion quantum yield. For TTA upconversion, triplet sensitizers and acceptors are combined to harvest the irradiation energy and to acquire emission at higher energy through triplet-triplet energy transfer (TTET) and TTA processes. Currently the triplet sensitizers are limited to the phosphorescent transition metal complexes, for which the tuning of UV-vis absorption and T(1) excited state energy level is difficult. Herein for the first time we proposed a library of organic triplet sensitizers based on a single chromophore of boron-dipyrromethene (BODIPY). The organic sensitizers show intense UV-vis absorptions at 510-629 nm (ε up to 180,000 M(-1) cm(-1)). Long-lived triplet excited state (τ(T) up to 66.3 μs) is populated upon excitation of the sensitizers, proved by nanosecond time-resolved transient difference absorption spectra and DFT calculations. With perylene or 1-chloro-9,10-bis(phenylethynyl)anthracene (1CBPEA) as the triplet acceptors, significant upconversion (Φ(UC) up to 6.1%) was observed for solution samples and polymer films, and the anti-Stokes shift was up to 0.56 eV. Our results pave the way for the design of organic triplet sensitizers and their applications in photovoltaics and upconversions, etc.

Ru(Phen)(bpy) 2 (1) and its new derivatives (2-5) with pyrenyl or ethynylated pyrene and phenyl units appended to the 3-position of the phenanthroline (Phen) ligand were prepared and these complexes generate long-lived room temperature phosphorescence in the red and near IR range (600-800 nm). The photophysical properties of these complexes were investigated by UV-Vis absorption, luminescence emission, transient absorption spectra and DFT/TDDFT calculations. We found the luminescence lifetime (s)can be drastically extended by ligand modification (increased up to 140-fold), e.g. s ¼ 58.4 ms for complex 3 (with pyrenyl ethynylene appendents) was found, compared to s ¼ 0.4 ms for the reference complex 1. Ethynylated phenyl appendents alter the s also (complex 2, s ¼ 2.4 ms). With pyrenyl appendents (4 and 5), lifetimes of 2.5 ms and 9.2 ms were observed. We proposed three different mechanisms for the lifetime extension of 2, 3, 4 and 5. For 2, the stabilization of the 3 MLCT state by p-conjugation is responsible for the extension of the lifetime. For 3, the emissive state was assigned as an intra-ligand (IL) long-lived 3 p-p* state ( 3 IL/ 3 LLCT, intraligand or ligand-to-ligand charge transfer), whereas a C-C single bond linker results in a triplet state equilibrium between 3 MLCT state and the pyrene localized 3 p-p* triplet state ( 3 IL, e.g. 4 and 5). DFT/TDDFT calculations support the assignment of the emissive states. The effects of the lifetime extension on the oxygen sensing properties of these complexes were studied in both solution and polymer films. With tuning the emissive states, and thus extension of the luminescence lifetimes, the luminescent O 2 sensing sensitivity of the complexes can be improved by ca. 77-fold in solution (I 0 /I 100 ¼ 1438 for complex 3, vs. I 0 /I 100 ¼ 18.5 for complex 1). In IMPES-C polymer films, the apparent quenching constant K SV app is improved by 150-fold from 0.0023 Torr À1 (complex 1) to 0.35 Torr À1 (complex 3). The K SV app value of complex 3 is even higher than that of PtOEP under similar conditions (0.15 Torr À1 ).

Phenols are widely used as starting materials in both industrial and academic society. Dearomatization reactions of phenols provide an efficient way to construct highly functionalized cyclohexadienones. The main challenge to make them asymmetric by catalytic methods is to control the selectivity while overcoming the loss of aromaticity. In this tutorial review, an up to date summary of recent progress in CADA reactions of phenol and aniline derivatives is presented.