Remarkable Off-On Tunable Solid-State Luminescence by the Regulation of Pyrene Dimer.

It is always a challenge to achieve "off-on" luminescent switch by regulating non-covalent interactions. Herein, we report a unique strategy for constructing high performance "off-on" tunable luminescent materials utilizing a novel molecule (TFPA) consist of pyrene and cyanostilbene. The pristine crystal of TFPA is almost non-emissive. Upon grinding/UV irradiation, an obvious luminescence enhancement is observed. Theoretical and experimental results revealed the underlying mechanism of this intriguing "off-on" switching behavior. The non-emissive crystal consists of ordered H-aggregates, with adjacent two molecules stacked in an anti-parallel manner and no overlapped area in pyrene moieties. When external force is applied by grinding or internal force is introduced through the photoisomerization, the dimer structures are facilitated with shorter intermolecular distances and better overlapping of pyrene moieties. In addition, the "on" state can recover to "off" state under thermal annealing, showing good reversibility and applicability in intelligence material. The present results promote an in-depth insight between packing structure and photophysical property, and offer an effective strategy for the construction of luminescence "off-on" switching materials, toward the development of stimuli-responsive luminescent materials for anti-counterfeiting.

Luminescent switch sensors for the detection of biomolecules based on metal-organic frameworks.

Metal-organic frameworks (MOFs) as sensing materials have experienced explosive growth in recent years due to their intrinsic merits, such as structural diversity, high porosity, large surface area, extraordinary adsorption affinities, etc. Biomolecules such as DNA, protein, and vitamins play vital roles in metabolism. Moreover, the sensitive detection of biomolecules is of importance in the disease prevention and treatment. This review intends to provide an update on the recent progress in the detection of various biomolecules via MOF-based luminescent sensors. MOFs are successful in the detection of DNA, RNA, protein, and other biomolecules. MOF-based luminescent sensors function by utilizing different mechanisms, including luminescent responses of enhancement and quenching, which are defined as "turn-on" and "turn-off" responses, respectively. Then, a short comparison of the "turn-on" and "turn-off" types of sensors is also made.

Aggregation-induced phosphorescence of iridium(III) complexes with 2,2'-bipyridine-acylhydrazone and their highly selective recognition to Cu2+.

Two cationic cyclometallated iridium(III) complexes with 2,2'-bipyridine-acylhydrazone were synthesized and characterized by spectroscopic and photophysical measurements. They exhibit remarkable aggregation-induced phosphorescent emission (AIPE) phenomenon which is caused by the restriction of rapid isomerization of the C=N bond in the acylhydrazone moiety and are supported by TD-DFT studies. They also act as a significant 'off-on' luminescent switch for Cu(2+) which works as both catalyzer and oxidant in the sensing process, resulting in hydrolysis and cyclization products which are highly emissive. The sensing properties of iridium(III) complexes are also investigated by ESI-MS spectrometry and (1)H NMR spectroscopy.

Pairing of Luminescent Switch with Electrochromism for Quasi-Solid-State Dual-Function Smart Windows.

Smart window is a promising green technology with feature of tunable transparency under external stimuli to manage light transmission and solar energy. However, more functions based on the intelligent management of the solar spectrum need to be integrated into present smart windows. In this work, a dual-function smart window is fabricated by pairing the luminescent switch with the electrochromic window. The dual function is based on a single fluorine doped tin oxide coated glass functionalized with tungsten oxide and copper nanocluster, among which tungsten oxide serves as an electrochromic material and copper nanocluster provides photoinduced luminescence. Along with the regulation of the visible light based on the electrochromism of the window, the luminescence can be finely switched on and off, which establishes a pair of reversible states ("on" and "off") for the dual-function smart window. The contrast between two states reaches 88%. Furthermore, the manipulation of dual-function smart window is highly reversible with a short response time of 12.6 s. This prototype of dual-function smart window paves the way for developing multifunctional smart windows by integrating different functional materials into one smart window based on the rational management of the solar spectrum.

A long-lived phosphorescence iridium(III) complex as a switch on-off-on probe for live zebrafish monitoring of endogenous sulfide generation.

In this work, we report a novel iridium(III)-based luminescent switch on-off-on probe, for the in vitro and in vivo detection of sulfide ion. The mechanism of this platform is based on the effective charge transfer quenching of the iridium(III) complex 1 by Fe3+, followed by the restoration of luminescence upon the addition of Na2S. The probe, hereinafter referred to as 1-Fe3+, exhibited a linear range of detection for Na2S from 0.01 to 1.5mM, with a detection limit of 2.9µM at signal-to-noise ratio (S/N) of 3. We also demonstrate the utility of 1-Fe3+ for cell-based imaging as well as for the detection of enzymatic sulfide generation in living zebrafish.

Reversible luminescence switching in a ruthenium(II) bis(2,2':6',2''-terpyridine)-benzoquinone dyad.

An electroactive luminescent switch has been synthesized that comprises a hydroquinone-functionalized 2,2':6',2''-terpyridine ligand coordinated to a ruthenium(II) (4'-phenylethynyl-2,2':6',2''-terpyridine) fragment. The assembly is sufficiently rigid that the hydroquinone-chromophore distance is fixed. Excitation of the complex via the characteristic metal-to-ligand charge-transfer (MLCT) absorption band produces an excited triplet state in which the promoted electron is localized on the terpyridine ligand bearing the acetylenic group. The triplet lifetime in butyronitrile solution at room temperature is 46 +/- 3 ns but increases markedly at lower temperature. Oxidation of the hydroquinone to the corresponding benzoquinone switches on an electron-transfer process whereby the MLCT triplet donates an electron to the quinone. This reaction reduces the triplet lifetime to 190 +/- 12 ps and essentially extinguishes emission. The rate of electron transfer depends on temperature in line with classical Marcus theory, allowing calculation of the electronic coupling matrix element and the reorganization energy as being 22 cm(-1) and 0.84 eV, respectively. The switching behavior can be monitored using luminescence spectroelectrochemistry. The on/off level is set by temperature and increases as the temperature is lowered.