Chirality is a particularly important concept in nature and exists at all length scales, ranging from the molecular level to the supramolecular level. Over the last two decades, various design strategies have been developed to construct chiral materials based on perylene diimides (PDIs) and to mimic the chiral assembly process in biological systems, but applications of these chiral aggregates are still at an early stage. This Minireview summarizes recent progress in the synthesis and properties of chiral PDIs. The chirality in PDI‐based materials can be generated by three different approaches: from the twisted planes of PDIs, the chiral substituents of PDIs, and the co‐assembly of achiral PDIs and chiral guests. A comprehensive understanding of the applications of chiral PDIs as well as potential future developments is also provided.

No abstract

The unstable radium nucleus is appealing for probing new physics due to its high mass, octupole deformation and energy level structure. Ion traps, with long hold times and low particle numbers, are excellent for work with radioactive species, such as radium and radium-based molecular ions, where low activity, and hence low total numbers, is desirable. We address the challenges associated with the lack of stable isotopes in a tabletop experiment with a low-activity (∼ 10 µCi) source where we laser-cool trapped radium ions. With a laser-cooled radium ion we measured the 7p 2 P o 1/2 state's branching fractions to the ground state, 7s 2 S 1/2 , and a metastable excited state, 6d 2 D 3/2 , to be p = 0.9104(7) and 0.0896 (7), respectively. With a nearby tellurium reference line we measured the 7s 2 S 1/2 → 7p 2 P o 1/2 transition frequency, 640.096 63(6) THz.Radium, the heaviest alkaline earth element, has no stable isotopes. Singly ionized radium's simple electronic structure is amenable to optical pumping and laser cooling with wavelengths far from the challenging UV of most alkaline earth type ions. Radium's heavy nucleus, atomic number Z = 88, is well suited to searches for new physics, where sensitivity to symmetry breaking forces scales ∝ Z 3 [1, 2]. Certain radium isotopes, such as radium-225, have additional nuclear structure enhancements to CP (charge-parity) violating new physics [3,4]. Setting limits to sources of CP violation will help us understand the baryon asymmetry in the observed Universe [5].Pioneering work with trapped HfF + molecular ions has made significant progress in constraining leptonic CP violation, and has rigorously studied potential systematic effects for future experiments [6]. A complementary hadronic CP violation experiment with radioactive molecular ions RaOH + , or RaCOH + 3 [7] is an intriguing possibility, where the low densities and long hold times of ion traps are well matched to working with radioactive isotopes, because low total activity is desirable. The radium-225 nucleus (I = 1/2) has octupole deformed parity doublets that enhance sensitivity to CP violating forces by a factor of 100-1000 compared to the current touchstone atomic system, 199 Hg [8-10]. A radiumbased molecular ion, such as 225 RaOH + , has an additional sensitivity advantage because of the molecule's closely spaced, opposite parity electronic states in addition to the enhancements from the closely spaced, opposite parity radium nuclear states. Trapped and lasercooled radium ions could be the starting point for generating such radium-based molecular ions, where optical pumping Ra + may provide control of chemical reactions to produce RaOH + , as seen in other alkaline earth ions Ca + and Be + [11,12].A single laser-cooled radium ion is also a candidate for atomic parity nonconservation (PNC) measurements, as the massive radium nucleus enhances PNC effects and the simple electronic structure is appealing for the requisite calculations [13,14]. There are many radium isotopes, including several that were previo...

Organic room-temperature phosphorescence (RTP) materials have been paid great attention for their promising applications in anticounterfeiting, optical device, and bioimaging. However, owing to inefficient intersystem crossing (ISC), it still remains a challenge to develop organic RTP materials with both high quantum yields (Φ p ) and long lifetime (τ p ). Herein, a reasonable strategy is presented to modulate and balance the Φ p and τ p through the synergy effect of halogen bonding and heavyatom effect (HAE). Modulated RTP properties are successfully achieved by the introduction of halogen atoms into 4-(9-Hcarbazol-9-yl) benzonitrile due to enhanced ISC. Especially, CzBzBr shows the highest Φ p of 23.50% and CzBzCl exhibits the longest τ p of 607.4 ms. The excessive HAE of the bromine atom decreases the τ p of CzBzBr, while moderate HAE of the chlorine atom endows CzBzCl with both high Φ p and long τ p . In addition, the halogen bondings lead to specific halogen-mediated molecular cluster packing, further suppressing nonradiative transition for ultralong RTP emission. Through simple physical co-crystallization with adjusting the mass ratio of CzBzCl/CzBzBr, co-crystals with modulated RTP properties and white-light emission phenomena are obtained. Our study provides a rationale method to develop modulated high-efficiency RTP materials, which will expand their practical applications.

No abstract

Organic room temperature phosphorescent (RTP) materials have potential applications in the fields of bioimaging, anti-counterfeiting, and displays. However, developing organic RTP materials with ultralong lifetime are still difficult due to...

We report the first driving of the 7s 2 S 1/2 → 6d 2 D 3/2 and 7s 2 S 1/2 → 6d 2 D 5/2 electric quadrupole (E2) transitions in Ra + . We measure the frequencies of both E2 transitions, and two other lowlying transitions in 226 Ra + that are important for controlling the radium ion's motional and internal states: 6d 2 D 3/2 → 7p 2 P o 3/2 and 6d 2 D 5/2 → 7p 2 P o 3/2 . arXiv:1910.06351v2 [physics.atom-ph] 1 Jan 2020

No abstract