There has been much interest in dual-emission materials in the past few years for materials and life science applications;h owever, asystematic overview of the underlying processes is so-far missing.We resolve this issue herein by classifying dual-emission (DE) phenomena as relying on one emitter with two emitting states (DE1), two independent emitters (DE2), or two correlated emitters (DE3). Relevant DE mechanisms for materials science are then briefly described together with the electronic and/or geometrical conditions under which they occur.F or further reading,references are given that offer detailed insight into the complex mechanistic aspects of the various DE processes or provide overviews on materials families or their applications. By avoiding ambiguities and misinterpretations,t his systematic, insightful Review might inspire future targeted designs of DE materials.

A highly efficient organic photocatalyst (OPC) for photoinduced electron/energy-transfer reversible addition–fragmentation chain-transfer (PET-RAFT) polymerization was identified through a systematic catalyst design and discovery. The devised OPC offers excellent control over PET-RAFT polymerizations of methyl methacrylate at very low catalyst loadings (5 ppm), that is, ca. 5–50 times lower loadings than other OPCs reported so far. Moreover, excellent oxygen tolerance was achieved using the discovered OPC combined with trithiocarbonate-based chain-transfer agent (CTA) under low-energy light irradiation conditions. In depth experimental and computational investigations revealed that (1) strong visible-light absorption and efficient generation of long-lived triplet states of the OPC due to its unique molecular structure and (2) the oxidation stability and no rate retardation of trithiocarbonate-based CTA are the key to the outstanding oxygen tolerance and ppm-level catalyst loadings. Our approach is thus believed to address a variety of challenging tasks related to polymer synthesis and living additive manufacturing.

The spectral characteristics of N,N-dimethyl-4-(4-methyl-4H-imidazo[4,5-b]pyridin-2-yl)benzenamine (PyN-Me), 1-methyl-2-(4'-(N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (ImNH-Me), and 2-phenylimidazo[4,5-b]pyridine (PIP) are investigated to understand the mechanism of protic solvent induced dual fluorescence of 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b). No dual emission is observed from PyN-Me where pyridyl nitrogen blocked from hydrogen bonding with protic solvents confirms the importance of hydrogen bonding of protic solvents with the pyridyl nitrogen in dual emission of DMAPIP-b. Like DMAPIP-b, ImNH-Me also exhibits weak emission and has a shorter fluorescence lifetime in methanol. However, single emission is observed from ImNH-Me in all solvents including protic solvents. This suggests that the imidazole >NH hydrogen also plays a role in the dual emission process. The longer wavelength emission of DMAPIP-b in water increases with increase in pH of the solution owing to deprotonation of the imidazole >NH group. On the basis of these results, the mechanism for the dual emission of DMAPIP-b is proposed.

Several theoretical studies have proposed strategies to reach helical molecular orbitals (Hel-MOs) in [n]cumulenes. While chiral even-[n] cumulenes feature Hel-MOs, odd-[n] cumulenes may also present them if the terminal groups lie on different planes. However, the hitherto proposed systems have been either experimentally unfeasible or resulted in opposite pseudodegenerated Hel-MOs, impeding their use in real applicatons. To overcome this challenge, we hereby demonstrate the introduction of a remarkable energy difference between helical orbitals of opposite twist by fixing the torsion angle between the terminal groups in butadiyne fragments. In order to experimentally lock the conformation of the terminal groups, we designed cyclic architectures by combining acetylenes with chiral spirobifluorenes. A straightforward synthetic strategy along with the high stability allowed the isolation and full characterization of systems presenting distinct helical orbitals. Finally, a thorough computational analysis revealed that the most significant optical responses of these systems originate mainly from the exciton coupling between the featured diphenylbutadiyne fragments. This novel strategy opens now access to the development of systems with distinct helical molecular orbitals suitable for their implementation into chiroptical and optoelectronic applications Scheme 1. General representation of acetylene (top left), [2]cumulene (top center), [3]cumulene (top right) and schematic representation of two possible paths for the formation of helical orbitals in [2]cumulenes (bottom left) and acetylenes (bottom right). Black spheres represent functional groups that can be the same or different and grey lobes stand for p atomic orbitals.

We report the design and synthesis of a series of room temperature phosphorescent phosphoramides TPTZPO, TPTZPS, and TPTZPSe with donor (Phenothiazine)-acceptor (P=X, X=O, S, and Se) architecture. All the compounds...