Influence of Supramolecular Interactions on Electron-Transfer Photochromism of the Crystalline Adducts of 4,4′-Bipyridine and Carboxylic Acids

Abstract

We have studied the electron-transfer photochromism of the crystalline adducts of 4,4′-bipyridine (Bpy) and carboxylic acids and revealed the key structural parameters that decide whether the photochromism can happen for the first time. Experimental and theoretical analyses on nine known examples showed that the hydrogen bonds, instead of π–π stacking interactions, are the defining factor to the photochromism. Only the presence of N–H···O hydrogen bonds can fulfill the electron transfer from the carboxylate group to the Bpy part, although both the N···O separations of O–H···N and N–H···O hydrogen bonds are suitable for the so-called through-space electron transfer. These results can not only help to screen out the photochromic species from the known hundreds of Bpy–carboxylic acid adducts deposited in the Cambridge Crystallographic Data Centre (CCDC) database but also guide the design and syntheses of new adducts using diverse N-heterocyclic aromatic molecules and carboxylic acids.

A Multifunctional MnII Phosphonate for Rapid Separation of Methyl Orange and Electron‐Transfer Photochromism

“…The structures were solved by direct methods and refined on F 2 by full-matrix least-squares techniques using SHELXTL-97. [28] All non-hydrogen atoms were refined with anisotropic displacement parameters during the final cycles. All hydrogen atoms of the organic molecule were placed on the basis of geometrical considerations and were added to the structure factor calculation.…”

“…Data processing was accomplished with the SAINT program. The structures were solved by direct methods and refined on F 2 by full‐matrix least‐squares techniques using SHELXTL‐97 . All non‐hydrogen atoms were refined with anisotropic displacement parameters during the final cycles.…”

A Smart Photochromic Semiconductor: Breaking the Intrinsic Positive Relation Between Conductance and Temperature

“…200 mW cm −2 ), the as‐synthesized crystalline sample of 1 underwent a clear color change from colorless ( 1 A ) to purple ( 1 B ) (Figure ). As reported, the photoinduced coloration of 1 originated from a PIET process from the (Hox) − anions to the (H 2 bipy) 2+ cations through the hydrogen bonds and the formation of stable radicals. The 1 B sample retained the radicals and the purple color in the dark in air for several months at room temperature (RT; Supporting Information, Figure S4).…”

Ionothermal synthesis of a photochromic inorganic–organic complex for colorimetric and portable UV index indication and UVB detection

“…The observed peaks are similar to the characteristic absorption of one-electron reduced species of viologen compounds via photoinduced electron transfer (PIET). 16,28 In situ time dependent UV-Vis spectra monitored at 599 nm indicated that the PIET process followed a rst order reaction kinetics, with a rate constant k obs of 0.195 s À1 , which was much higher than that of some reported viologen-based photochromic compounds (2.324 Â 10 À4 s À1 to 1.5 Â 10 À2 s À1 ), 31,32 indicating its superior photoresponsive rate (Table S3 †). NEU20-P could be retained under ambient conditions for several months with no naked eyedetectable color change, indicating an ultralong-lived chargeseparated state and excellent colored stability upon UV irradiation, which may be attributed to the p-p stacking interactions and the dense packing mode of bpy/H 2 bpy 2+ dications that stabilized the generated radicals and prevented the electron transfer between the radicals and inorganic clusters.…”

“…1a) ), and maybe the potential paths for the through-space electron transfer. [28][29][30] In addition, p-p stacking interactions were found between the adjacent pyridinium rings of the bpy and H 2 bpy 2+ dications with face-to-face distances from 3.514(108)Å to 3.730(87)Å (Fig. 1b).…”