Unraveling the Mechanisms of the Excited-State Intermolecular Proton Transfer (ESPT) for a D-π-A Molecular Architecture.

Precise revealing the mechanisms of excited-state intermolecular proton transfer (ESPT) and the corresponding geometrical relaxation upon photoexcitation and photoionization remains a formidable challenge. In this work, the compound (E)-4-(((4H-1,2,4-triazol-4-yl)imino)methyl)-2,6-dimethoxyphenol (TIMDP) adopting a D-π-A molecular architecture featuring a significant intramolecular charge transfer (ICT) effect has been designed. With the presence of perchloric acid (35 %), TIMDP can be dissolved through the formation of a HClO4 -H2 O-OH(TIMDP)-N(TIMDP) hydrogen-bonding bridge. At the ground state, the ICT effect is dominant, giving birth to crystals of TIMDP. Upon external stimuli (e.g., UV light irradiation, electro field), the excited state is achieved, which weakens the ICT effect, and significantly promotes the ESPT effect along the hydrogen-bonding bridge, resulting in crystals of [HTIMDP]+ ⋅[H2 O]⋅[ClO4 ]- . As a consequence, the mechanisms of the ESPT can be investigated, which distorted the D-π-A molecular architecture, tuned the emission color with the largest Stokes shift of 242 nm, and finally, high photoluminescence quantum yields (12 %) and long fluorescence lifetimes (8.6 µs) have achieved. These results not only provide new insight into ESPT mechanisms, but also open a new avenue for the design of efficient ESPT emitters.

Porous High-Valence Metal-Organic Framework Featuring Open Coordination Sites for Effective Water Adsorption.

The design and preparation of a porous high-valence metal-organic framework (MOF) featuring open coordination sites are of utmost importance for the development of adsorbent materials. Here in this work, the three-dimensional (3D) high-valence MOF [Er(dcbp)3/2(DMF)(H2O)2]·2H2O (HV-MOF-1; H2dcbp = 4,4'-dicarboxy-2,2'-bipyridine, DMF = N,N-dimethylformamide), which possesses permanent porosity and two open coordination sites, has been prepared and characterized. In the 3D framework, the dcbp molecules display two different bridging styles, resulting in ordered diamondlike pores with bared carboxyl oxygen and pyridine nitrogen atoms on dcbp exposed directly to the pores, generating hydrophilic characteristics and high water affinity. In addition, the open coordination sites act as arms to fix the adsorbed water molecules, providing high water adsorption capacity (5.95 mmol g-1) and selectivity. More importantly, the activated HV-MOF-1 species shows an energy-saving step for recycling (operation under 120 °C), demonstrating promise as a candidate for an adsorbent material with considerable water adsorption-desorption cycles.

Ambient-Temperature Spin-State Switching Achieved by Protonation of the Amino Group in [Fe(H2Bpz2)2(bipy-NH2)].

Magnetism of a complex [Fe(H2Bpz2)2(bipy-NH2)] (H2Bpz2 = dihydrobis(1-pyrazolyl)borate, bipy-NH2 = 4,4'-diamino-2,2'-bipyridine) has been altered from paramagnetic to spin-crossover (SCO) behavior, through protonation of one amino group of bipy-NH2 with CF3SO3H. Complete SCO transition, both in solid state and in solution, occurs at ambient temperature.

Construction and screening of spin-crossover-sponge materials based on iron(II)-triazole coordination polymers.

Iron(II)-triazole coordination polymers have attracted considerable interest for their synthetic versatility, which allows tuning their spin-crossover (SCO) properties. Embedding SCO solid particles in sponge matrices is a simple, powerful, and generic approach to construct processable SCO materials. Here, we have studied a series of magnetic frameworks based on partial ligand substitution by using different chemical mixtures of two organic ligands, yielding four isostructural coordination polymers. The integration of the hygroscopic SCO material has endowed the composite sponge with the ability to capture moisture under ambient conditions. In particular, not only does a spin-crossover transition during absorption occur, but also a color variation has been achieved by varying humidity. The consequences of cooperativity and the exposed surface of the composite sponge on the spin transition were evaluated and the most promising materials among them were screened. This work provides guiding significance for the fabrication and practical application of spin-crossover-sponge materials.

Dynamic Aggregation Triggering Reversible Spin-State Switching.

The manipulation of spin-state switching (SSS) under ambient conditions is of significant importance for the construction of molecular switches. Herein, we demonstrate that reversible SSS can be mediated by the aggregation state of a near-infrared (NIR)-sensitive ferrous complex. The ferrous complex was J-aggregated in a DMF suspension and with a low-spin (LS) state; however, with the addition of water, it changed to H-aggregation and reached a high-spin (HS) state, owing to the enhanced intramolecular charge transfer and metal-to-ligand charge transfer. Interestingly, the following NIR irradiation can restore the J-aggregation and LS states owing to the enhanced ligand-to-ligand charge transfer. More interestingly, the ferrous complex can be further incorporated into a hygroscopic sponge that was capable of capturing humidity effectively for all weather conditions, which displayed reversible SSS via alternating atmospheric humidity capture and NIR irradiation under ambient conditions in the sponge state. This study thus opens up a new avenue for the development of novel smart molecular switches at the device level.

Porous Calcium-Silicate-Hydrate as a Low-Cost Nano-Platform for Ultra-High CO2 Capture and Storage.

CO2 capture and storage have been regarded as promising concepts to reduce anthropogenic CO2 emissions. However, the high cost, inferior adsorption capacity, and higher effective activation temperature of traditional sorbents limit their practical application in efficient CO2 capture. Here, a C-S-H@ZIF-8 (C-S-Z) sorbent is fabricated by in situ growth of the ZIF-8 shell on the C-S-H (calcium-silicate-hydrate) surface for ultra-high CO2 adsorption and storage. Among the C-S-Z, the outer ZIF-8 shell acts as a transport channel that promotes CO2 absorption toward the underlying C-S-H substrate for accelerated carbonation while preventing nitrogen and water from reaching the interior C-S-H. As a consequence, C-S-Z possesses the merits of ample pyrrolic nitrogen, porous structure, and ultra-high surface area (577.18 m2  g-1 ), that contribute to an ultra-high CO2 capture capacity, reaching 293.6 mg g-1 . DFT calculations show a high CO2 adsorption energy and the mineral carbonation is dominant by the adsorption process. In particular, the advantages of the outstanding adsorption capacity, low cost, and high CO2 selectivity make this C-S-H-based sorbent hold great potential in the practical application for direct air CO2 capture and storage.

Paliperidonium nitrate.

In the title mol-ecular salt (systematic name: 3-{2-[4-(6-fluoro-1,2-benzoxazol-3-yl)piperidin-1-yl]eth-yl}-9-hy-droxy-2-methyl-1,6,7,8,9,9a-hexa-hydro-pyrido[1,2-a]pyrimidin-4-one nitrate), C(23)H(29)FN(4)O(3) (+)·NO(3) (-), the piperidine ring displays a chair conformation and its N atom is protonated; the N-H bond is in an axial orientation. The ring bearing the hy-droxy group exhibits a half-chair conformation. The hy-droxy group as well as the adjacent methyl-ene group are disordered over two sets of sites in a 0.823 (5):0.177 (5) ratio. In the crystal, O-H⋯N, O-H⋯O, N-H⋯O and N-H⋯N hydrogen bonds connect the components into a three-dimensional network.

6-Fluoro-1H-indole-3-carb-oxy-lic acid.

In the title compound, C(9)H(6)FNO(2), all the non-H atoms are approximately coplanar, the carb-oxy O atoms deviating by 0.0809 and -0.1279 Šfrom the indole plane. In the crystal, O-H⋯O hydrogen bonds link the mol-ecules into dimers which are linked via N-H⋯O hydrogen bonds and π-π inter-actions [centroid-centroid distance = 3.680 (2) Å].

2-(4-Meth-oxy-1H-indol-3-yl)acetonitrile.

In the title compound, C(11)H(10)N(2)O, the cyanide group is twisted away from the indole-ring plane [C(cy)-C(me)-C(ar)-C(ar) = 70.7 (2)°; cy = cyanide, me = methyl-ene, ar = aromatic], whereas the meth-oxy C atom is almost coplanar with the ring system [displacement = 0.014 (5) Å]. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into C(7) chains propagating in [100].

2-(6-Chloro-1H-indol-3-yl)acetonitrile.

In the title compound, C(10)H(7)ClN(2), the carbonitrile group is twisted away from the plane of the indole ring system [C(cy)-C(me)-C(ar)-C(ar) = -44.7 (8)°; cy = cyanide, me = methyl-ene and ar = aromatic]. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into C(7) chains propagating in [010]. Aromatic π-π stacking inter-actions [minimum centroid-centroid separation = 3.663 (3) Å] are also observed.

5-Chloro-1H-indole-3-carb-oxy-lic acid.

In the title compound, C(9)H(6)ClNO(2), the carboxyl group is twisted from the indole ring system by 9.00 (8)°. In the crystal, inversion dimers linked by pairs of O-H⋯O hydrogen bonds generate R(2) (2)(8) loops and N-H⋯O hydrogen bonds link the dimers into (001) sheets. Aromatic π-π stacking inter-actions [centroid-centroid distance = 3.7185 (12) A °] are also observed.

5-Fluoro-1H-indole-3-carb-oxy-lic acid.

In the title compound, C(9)H(6)FNO(2), the carboxyl group is twisted slightly away from the indole-ring plane [dihedral angle = 7.39 (10)°]. In the crystal, carboxyl inversion dimers linked by pairs of O-H⋯O hydrogen bonds generate R(2) (2)(8) loops and N-H⋯O hydrogen bonds connect the dimers into (10[Formula: see text]) sheets.

6-Chloro-quinolin-2(1H)-one.

In the title compound, C(9)H(6)ClNO, the Cl atom deviates by 0.142 (1) Šfrom the quinoline ring mean plane (r.m.s. deviation = 0.013 Å). In the crystal, N-H⋯O hydrogen bonds link the mol-ecules into [010] C(4) chains. Aromatic π-π stacking inter-actions [shortest centroid⋯centroid distance = 3.685 (3) Å] are also observed.

2-(4-Chloro-1H-indol-3-yl)acetonitrile.

The title compound, C(10)H(7)ClN(2), contains two approximately planar mol-ecules, A and B (r.m.s. deviations = 0.039 and 0.064 Å, respectively) in the asymmetric unit. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into C(7) chains of alternating A and B mol-ecules propagating along the a-axis direction. The crystal used for the data collection was found to be a racemic twin.

4-Nitro-isophthalic acid.

In the crystal structure of the title compound, C(8)H(5)NO(6), both carboxyl groups are involved in inter-molecular centrosymmetric cyclic O-H⋯O hydrogen-bonding associations, which give a zigzag chain structure extending along (2[Formula: see text]1). Weak π-π stacking inter-actions are also present [minimum ring centroid separation = 3.893 (4) Å].

3-[(E)-2-Phenyl-ethen-yl]-1H-indole-6-carbonitrile.

In the title compound, C(17)H(12)N(2), the inter-planar angle between the indole mean plane [max.deviation 0.030 (1) Å] and the phenyl ring is 24.32 (7)°. In the crystal, inter-molecular N-H⋯N C hydrogen bonds form zigzag chains in the a-axis direction augmented by weak C-H⋯N C contacts.

(5-Meth-oxy-1H-indol-3-yl)acetonitrile.

In the title compound, C(11)H(10)N(2)O, the O atom and the C atom of the methyl-ene group deviate only slightly [0.029 (3) and 0.055 (3) Å, respectively] from the approximately planar ring system (r.m.s. deviation = 0.013 Å). In the crystal, N-H⋯O hydrogen bonds link the mol-ecules into zigzag chains running along the b axis.

6-[(E)-2-Phenyl-vin-yl]-1H-indole.

The title compound, C(16)H(13)N, is essentially planar [maximum deviation from the least-squares plane = 0.081 (3) Å], with a dihedral angle of 1.65 (13)° between the planes of the indole and benzene rings. In the crystal, there are no significant inter-molecular π-π inter-actions [minimum ring centroid-centroid separation = 4.217 (5) Å].

2-(7-Methyl-1H-indol-3-yl)acetonitrile.

In the title compound, C(11)H(10)N(2), the carbonitrile group is twisted away from the indole plane [C(cy)-C(me)-C(ar)-C(ar) = 66.6 (2)°; cy = cyanide, me = methyl-ene and ar = aromatic]. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into C(7) chains propagating in the [001] direction.

2,4-Dibromo-6-[(hydroxyimino)methyl]phenol.

In the title compound, C(7)H(5)Br(4)NO(2), intra-molecular O-H⋯N hydrogen bonds are observed. In the crystal structure, inter-molecular O-H⋯O hydrogen bonds link the mol-ecules into dimers.