Boron-dipyrrin chromophores containing a 5-aryl group with or without internal steric hindrance toward aryl rotation have been synthesized and then characterized via X-ray diffraction, static and time-resolved optical spectroscopy, and theory. Compounds with a 5-phenyl or 5-(4-t-butylphenyl) group show low fluorescence yields (∼0.06) and short excited-singlet-state lifetimes (∼500 ps), and decay primarily (>90%) by nonradiative internal conversion to the ground state. In contrast, sterically hindered analogues having an o-tolyl or mesityl group at the 5-position exhibit high fluorescence yields (∼0.9) and long excited-state lifetimes (∼6 ns). The X-ray structures indicate that the phenyl or 4-tert-butylphenyl ring lies at an angle of ∼60°with respect to the dipyrrin framework whereas the angle is ∼80°for mesityl or o-tolyl groups. The calculated potential energy surface for the phenylsubstituted complex indicates that the excited state has a second, lower energy minimum in which the non-hindered aryl ring rotates closer to the mean plane of the dipyrrin, which itself undergoes some distortion. This relaxed, distorted excited-state conformation has low radiative probability as well as a reduced energy gap from the ground state supporting a favorable vibrational overlap factor for nonradiative deactivation. Such a distorted conformation is energetically inaccessible in a Supporting Information Available: Theoretical analysis of the excited-state surfaces and Franck-Condon-active modes for selected compounds, static absorption and emission spectra, time-resolved absorption and emission spectra, and ORTEP diagrams of the structures. Crystallographic data is available as CIF files. This material is available free of charge via the Internet at http://pubs.acs.org. NIH Public Access

Recently, because of their cost effectiveness, high safety and environmental friendliness, zinc-ion batteries (ZIBs) are receiving enormous attention. Until now, aqueous-based ZIBs have been the focus of attention. However, the issues regarding hydrogen evolution, and zinc electrode passivation as well as dendrite formation limit their practical application. In this work, a biocompatible, stable and low-cost choline chloride/ urea (ChCl/urea) deep eutectic solvent is reported as an alternative electrolyte for rechargeable ZIBs based on delta-type manganese oxide (δ-MnO 2 ) intercalation electrode. The behavior of the zinc electrode on stripping and deposition in ChCl/urea electrolyte was examined. Besides, the charge storage and charge-transfer characteristics of the battery was studied. The results showed that there was no sign of dendrite formation on the zinc electrode during long-term cycling. Consequently, the fabricated battery exhibited good electrochemical performance with the maximum specific capacity of 170 mAh/g and good cyclability. In addition, the system showed reversible plating/stripping of zinc (Zn) without dendrite formation and no passivation layer on the zinc electrode. Hence, the results confirmed the reversible intercalation of Zn from the deep eutectic solvent ChCl/urea into the δ-MnO 2 electrode. Overall, the proposed electrolyte shows good promise for Zn/δ-MnO 2 battery system.