Role of flexible bulky groups and weak interactions involving halogens in the vapoluminescence of a metal-free dye

Abstract

The vapoluminescence of a 2,5-diamino-3,6-dicyanopyrazine dye was correlated with molecular flexibility of bulky substituents and weak interactions involving halogens.

Tuning of fluorescence efficiency via local modification of the crystal structure by benzyl groups in polymorphs of a pyrazine dye

“…Amorphous forms (1Y, 1YO, 1Osolv, 1R, and 1RV), 10 where Y, YO, DO, Osolv, R, and RV represent the colors of the respective crystals: yellow, yellowish orange, dark orange, orange solvate, red, and reddish violet. The crystal structures of 1Y, 1YO, 1Osolv and 1R were reported.…”

“…The crystal structures of 1Y, 1YO, 1Osolv and 1R were reported. [10][11][12] In this study, the X-ray diffraction measurements of 1DO and 1RV were performed.…”

“…Absorption and emission spectra of 1Y, 1Osolv and 1 in CHCl 3 solution have been reported previously, 10 although the detailed analysis of fluorescence properties using photoluminescence lifetime data were not carried out. The absorption spectra of 1DO, 1R, 1RV, and an amorphous solid were corrected using a SIS-50 surface and interface spectrometer based on optical waveguide spectroscopy (System Instruments).…”

“…These measurement sets were the same as those of 1Y and 1Osolv, which have been reported previously. 10 The photoluminescence lifetimes of 1DO, 1Y, 1R, and an amorphous solid were determined using a Fluoro Cube fluorescence lifetime system (HORIBA). The excitation wavelength was 455 nm, and emission was monitored at 564 nm for 1DO, 558 nm for 1Y, 607 nm for 1R, and 615 nm for an amorphous solid.…”

“…1), which showed quite different fluorescence efficiencies between two polymorphs: a new polymorph with orange weak fluorescence and a previously reported polymorph with intense yellow fluorescence. 10 The results of crystal structure analysis indicated that the benzyl groups, which were not a part of the fluorophore of 1, played an essential role in tuning the fluorescence efficiency between the polymorphs via local modification of the crystal packing. This finding suggested that the introduction of benzyl groups to fluorophores can be an effective strategy for obtaining a compound with various solid-state fluorescence properties.…”