Central Ring Puckering Enhances the Stokes Shift of Xanthene Dyes

Small-molecule dyes are generally designed based on well-understood electronic effects. However, steric hindrance can promote excited-state geometric relaxation, increasing the difference between the positions of absorption and emission bands (the Stokes shift). Accordingly, we hypothesized that sterically induced central ring puckering in xanthene dyes could be used to systematically increase their Stokes shift. Through a combined experimental/quantum-chemical approach, we screened a group of (9-acylimino)-pyronin dyes with a perturbed central ring geometry. Our results showed that an atom with sp3 hybridization in position 10 of (9-acylimino)-pyronins induces central ring puckering and facilitates excited-state geometric relaxation, thereby markedly enhancing their Stokes shifts (by up to ~2000 cm-1). Thus, we prepared fluorescent (9-acylimino)-pyronin pH sensors, which showed a Stokes shift disparity between acid and base forms of up to ~8700 cm-1. Moreover, the concept of ring puckering-enhanced Stokes shift can be applied to a wide range of xanthene analogues found in the literature. Therefore, central ring puckering may be reliably used as a strategy for enhancing Stokes shifts in the rational design of dyes.

Desulfitative Sonogashira cross-coupling of thiopyronin for the synthesis of NIR arylacetylene-containing rhodamines

A classical, safe and efficient red-shift strategy contributing to NIR arylacetylene-containing rhodamines has been developed via the desulfitative Sonogashira cross-coupling reaction of thiopyronin for the first time, exhibiting a broad substrate scope with good yields. In addition, compound 3m shows great potential for application as a singlet oxygen probe, demonstrating the practicality of the method.

A Fluorescent Sensor for Dual-Channel Discrimination between Phosgene and a Nerve-Gas Mimic

The ability to analyze highly toxic chemical warfare agents (CWAs) and related chemicals in a rapid and precise manner is essential in order to alleviate serious threats to humankind and public security caused by unexpected terrorist attacks and industrial accidents. In this investigation, we designed a o-phenylenediamine-pyronin linked dye that is capable of both fluorogenic and colorimetric discrimination between phosgene and the prototypical nerve-agent mimic, diethyl chlorophosphate (DCP) in the solution or gas phase. Moreover, this dye has been used to construct a portable kit that can be employed for real-time monitoring of DCP and phosgene in the field, both in a discriminatory manner, and in a simple and safe way.

Tuning effects for some cyclic aromatic carbenes bearing remote amino groups

Yamamoto and co-workers synthesized two cyclic aromatic carbenes with remote amino groups. Here we theoretically studied related compounds to explore tuning effects on the singlet-triplet splitting by variations of functional groups. For the Yamamoto compound, the lowest singlet state lies 15.7 kcal/mol below the lowest triplet. The singlet-triplet separation is reduced by ∼7 kcal/mol when the dimethylamino groups are replaced by H. In one set of carbenes, when X = O, we substitute S, Se, Te, SO, SeO, and TeO for X; the resulting ΔE(S-T) predictions are 9.9, 7.3, 3.9, 4.3, 2.3, and -0.1 kcal/mol, respectively. A different set of X fragments yields triplet electronic ground states with ΔE(S-T) values of -8.6 (X = BH), -6.8 (X = AlH), -7.2 (X = GaH), -7.5 (X = InH), and -7.0 kcal/mol (X = TlH). We also predicted ΔE(S-T) with N(CH3)2 replaced by PH2, AsH2, SbH2, BiH2, BH2, CH3, OH, and F. Of all the molecules considered, that with N(CH3)2 replaced with BH2 and X = BH most favors the triplet state, lying 13.7 kcal/mol below the singlet. Finally, we have relocated the N(CH3)2 and NH2 groups from the (3, 6) positions to the (4, 5), (2, 7), and (1, 8) terminal ring positions, with very interesting results.

Gold(III)- versus gold(I)-induced cyclization: synthesis of six-membered mesoionic carbene and acyclic (aryl)(heteroaryl) carbene complexes

The golden state: selective 5-exo- and 6-endo-cyclizations of an alkynyl benzothioamide have been achieved. The selectivity is controlled by the oxidation state of the gold precursor (+I or +III), yielding two new types of carbene ligand: an (aryl)(heteroaryl)carbene and a six-membered mesoionic carbene. Mes=2,4,6-trimethylphenyl.