Development and Elucidation of a Novel Fluorescent Boron-Sensor for the Analysis of Boronic Acid-Containing Compounds

Novel boron-containing drugs have recently been suggested as a new class of pharmaceuticals. However, the majority of current boron-detection techniques require expensive facilities and/or tedious pretreatment methods. Thus, to develop a novel and convenient detection method for boron-based pharmaceuticals, imine-type boron-chelating-ligands were previously synthesized for use in a fluorescent sensor for boronic acid containing compounds. However, the fluorescence quantum yield of the imine-type sensor was particularly low, and the sensor was easily decomposed in aqueous media. Thus, in this paper, we report the development of a novel, convenient, and stable fluorescent boron-sensor based on O- and N-chelation (i.e., 2-(pyridine-2yl)phenol), and a corresponding method for the quantitative and qualitative detection of boronic acid-containing compounds using this commercially available sensor is presented

Diphenyldihydropentalenediones: Potential Singlet Fission Materials with High Triplet Energy Levels

2,2,5,5-Tetramethyl-3,6-diphenyl-2,5-dihydropentalene-1,4-dione (PD-H) was developed as a new molecular framework for singlet fission (SF) materials. It was proposed that PD-H and related substances would have high energy level of the triplet-excited state (ET) as a result of the enforcement of molecular planarity through incorporation of ring-fusion constrained diene and avoidance of resonance caused by the presence of amide moieties in the diketopyrrolopyrrole core. Three members of this family (PDs), PD-H, PD-OCH3 (the 4-methoxyphenyl derivative), and PD-CF3 (the 4-(trifluoromethyl)phenyl derivative), were synthesized. The results of photophysical studies revealed that the energy level of singlet-excited state (ES) and ET of PD-H are 2.88 and 1.43 eV, respectively. These values indicate that PD-H has the energy relationship, ES > 2ET, required for it to be a singlet fission material. Moreover, introduction of electron-donating or -withdrawing groups on the benzene rings in PD-H enable fine-tuning of ES and ET while maintaining ES > 2ET. The results of transient absorption spectroscopic studies show that PD-H, PD-OCH3, and PD-CF3 in CH2Cl2 have respective T1 lifetimes of 54, 94, and 108 microsec, which are long enough to utilize its triplet energy as an excitation energy in other optoelectronic systems. These findings suggest that diphenyldihydropentalenediones are potential candidates for SF materials with high ET levels

Elongation of Triplet Lifetime Caused by Intramolecular Energy Hopping in Diphenylanthracene Dyads Oriented to Undergo Efficient Triplet–Triplet Annihilation Upconversion

Triplet–triplet annihilation (TTA)-assisted photon upconversion (TTA-UC) in three dyads (DPA–Cn–DPA), comprised of two diphenylanthracene (DPA) moieties connected by nonconjugated C1, C2, and C3 linkages (Cn), has been investigated. The performance of these dyads as energy acceptors in the presence of the energy donor platinum octaethylporphyrin are characterized by longer triplet lifetimes (τT) and different TTA rate constants than those of the parent DPA. The larger tT of the linked systems, caused by “Intramolecular Energy Hopping” in the triplet dyad 3DPA*–Cn–DPA, results in a low threshold intensity, a key characteristic of efficient TTA-UC

Remarkable Piezofluorochromism of an Organoboron Complex Containing [2.2]Paracyclophane

Piezofluorochromism (PFC) of crystals of a tert-butyl and [2.2]paracyclophane-containing diaroylmethanatoboron difluoride (pCP-tBu), which is expected to possess both intermolecular and intramolecular – interactions, was investigated. pCP-tBu crystals were found to exhibit remarkable PFC associated with an over 150-nm redshift of fluorescence (FL) wavelength occurring under increasing isotropic pressure applied by using a diamond anvil cell. X-ray crystallographic analysis showed that pCP-tBu molecules in the crystal at atmospheric pressure exist in the form of an intermolecular pi-stacking dimer through back-to-back pi–pi interactions. Moreover, the crystallographic data under high pressure showed that increasing isotropic pressure causes a reduction in both the intermolecular -stacking distance of the dimer (DINTER) and the intramolecular pi-stacking distance between two benzene rings in the [2.2]paracyclophane moiety (DINTRA). Density functional theory calculations, using the Cartesian coordinates obtained by X-ray analysis, suggest that the origin of PFC of pCP-tBu crystals is the reduction of the LUMO energy of the pi-stacking dimer and that the intermolecular pi–pi interaction is still the important factor leading to PFC of pCP-tBu crystals

Long-lived Triplet Excitons Formed by Exergonic Intramolecular Singlet Fission of an Adamantane-linked Tetracene Dyad

An adamantane-linked tetracene dyad (Tc–Ad–Tc) undergoes exergonic intramolecular singlet fission (SF), producing longlived (τ = 175 μs) and high-energy (2 x 1.03 eV) multiexcitons. Timeresolved absorption, fluorescence decay, and electron paramagnetic resonance (EPR) spectroscopic analysis revealed that the long-lived triplet species is generated in this system via correlated triplet pair having singlet and quintet characteristics. Time-resolved EPR analysis revealed that conversion of 1(3Tc–Ad–3Tc)* -> 5(3Tc–Ad–3Tc)* requires small conformational dynamics accompanied by molecular motion. Analysis of the geometries of the quintet states shows that formation of the long-lived multiexciton is enabled by precise and close alignment of the tetracene moieties, which leads to their moderate interaction in the singlet excited state, while triplet–triplet annihilation is prevented by quintet generation. The presence of aliphatic linkages, like the rigid adamantane group, might enable effective conservation of intrinsic S1 and T1 levels of the original monomers, and moderate bridge-mediated σ–π interaction leading to exergonic intramolecular SF involving 1Tc*–Ad–Tc -> 1(3Tc–Ad–3Tc)*.</div