The Synthesis, Photophysical Characterization, and X‐Ray Structure Analysis of Two Polymorphs of 4,4′‐Diacetylstilbene

Abstract

A palladium(II) acetate-catalyzed synthesis of 1 that utilizes the novel triazene 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone as a synthon is described. The room temperature absorption spectra of 1 in various solvents exhibited a p ! p* transition in the range of 330 -350 nm. Compound 1 was observed to be luminescent, with room-temperature solution and solid-state emission spectra that exhibited maxima in the range 400 -500 nm. All room-temperature absorption and emission spectra exhibited some degree of vibrational structure. The emission spectrum of 1 at 77 K in propanenitrile glass was broad and featureless with a maximum at 447 nm. Compound 1 crystallized as a yellow and colorless polymorph. X-Ray structure analyses of both of these polymorphs and 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone are presented.Introduction. -For more than 45 years, numerous studies have been undertaken to characterize the unique excited-state properties of (E)-stilbene [1]. Towards the end of applying (E)-stilbene derivatives in a wide variety of research areas, this work has served as a catalyst for investigations into optimizing and tuning these excited-state properties by altering the functionality of (E)-stilbene [2] [3]. Of particular interest is the preparation of materials that contain an (E)-stilbene moiety. Such materials exhibit novel photophysical, redox, and electroluminescent properties that have potential applicability to the construction of light-emitting diodes and liquid-crystal displays [4].Our research involves the synthesis of unique ligands whose metal-binding moieties are positioned for the formation of luminescent metal-organic materials. A logical starting material for our ligands is 4,4'-diacetylstilbene (1; Scheme), with its synthetically versatile Ac groups and inherent luminescent properties. Since its first synthesis in 1945, its photophysical properties have been incompletely characterized [5]. In this article, we present a complete photophysical characterization of 1, which was found to absorb and emit light at longer wavelengths than (E)-stilbene. A new Pd-catalyzed synthesis of 1 is discussed and illustrated in the Scheme. The crystal structures of the yellow and colorless polymorphs of 1 are also presented.

Syntheses and crystal structure of 4-[(pyridin-3-yl)diazenyl]morpholine and 1-[(pyridin-3-yl)diazenyl]-1,2,3,4-tetrahydroquinoline

“…Examination of the structure of EMUDEX (Lee et al, 2016) suggests that a degree ofdelocalization across the linear triazene moiety of I was observed. The N2-N3 double-bond distance of 1.2679 (13) A ånd the N1-N2 single-bond distance of 1.3501 (12) A ˚in EMUDEX are in accordance with those reported for OFUBUO (Mukai et al, 2013), EZEXEN (Gholivand et al, 2010), FUZLUI (Pye et al, 2010). The structures of HAHQOZ (Johnson et al 2016), HUHGEZ (Isovitsch & Fronczek, 2020), IJEVUR (Gangwar et al, 2021), OPAVUX (Chin et al, 2011) and RUJQIX (Chin et al, 2009) feature similar intermolecular hydrogen-bonding interactions to those in I, resulting in supramolecular networks.…”