Dynamic characterization of crystalline fluorophores with conformationally flexible tetrahydrocarbazole frameworks. Issue 22 (20th May 2020)

• Record Type: Journal Article
• Authors: Colin-Molina, Abraham; Velázquez-Chávez, Diego; Jellen, Marcus J.; Rodríguez-Cortés, Lizbeth A.; Cifuentes-Quintal, Miguel Eduardo; Merino, Gabriel; Rodríguez-Molina, Braulio
• Is Part Of: CrystEngComm. Volume 22:Issue 22(2020)
• Page Start: 3789
• Page End: 3796
• Publication Date: 2020-05-20
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/d0ce00423e
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : Fluorescent compounds 2 and 3 have been prepared by using Ullmann-type coupling reactions. Solid-state NMR ( 13 C CPMAS and 2 H) and periodic DFT computations were used to determine that intramolecular motion coexists with emission in these crystals. Abstract : Two new compounds 2 and 3 and their deuterated analogues (2 - d 4 and 3 - d 4 ) were prepared from Ullmann-type coupling reactions. Both molecules show good emissive properties in solution Φ F = 0.13 (2 ) and 0.57 (3 ) as well as in the solid-state ( Φ F = 0.35 and 0.33, respectively). Variable temperature solid-state NMR measurements using 13 C CPMAS and 2 H spin-echo helped to identify segmental motion in the phenylene as well as in the aliphatic moieties, which agreed well with the crystallographic disorder in these moieties. The rotational energy barriers for the new compounds were computed with a periodic DFT approach, finding asymmetric rotational potentials with barriers of 3.5 kcal mol −1 (2 ) and 4.5 kcal mol −1 (3 ) for 60° jumps and much higher barriers (>25 kcal mol −1 ) for 180° jumps. Our studies indicate that low frequency 4-fold motions coexist with fluorescence in these crystalline conjugated compounds.