Solid-State Fluorescence of Tryptanthrin Analogs

Abstract

Tryptanthrin (T) and 2-fluorotryptanthrin (T2F) exhibit no fluorescence in the solid state. The presumption exists that this is due to the strong π-π stacking interaction resulting from the planar structure. However, the analogs, DCM-T and DCM-T2F, in which the 6-position carbonyl group is replaced with a stronger electron-withdrawing group, the dicyanomethylene group, exhibit fluorescence in the solid state despite the planar structure. The reasons for this were analyzed and discussed based on the results of X-ray crystal structure analysis.

Aggregation-induced Emission and Solid-State Fluorescence of 2-(4-(<i>N</i>,<i>N</i>-diphenylamino)phenyl)tryptanthrin

“…Nevertheless, in high concentration solutions, the rotational movement of the phenyl group is suppressed, favoring a light-emitting radiative process that leads to the emission of fluorescence. The introduction of an electron-donating group at the 2-position of tryptanthrin 6,7) , an antimicrobial substance extracted from plants like indigo, is known to result in outstanding fluorescent properties [8][9][10][11][12][13][14][15][16][17][18][19][20] . However, in highly concentrated solutions, π-π stacking interactions in fluorescent tryptanthrin compounds with planar structures cause fluorescence quenching.…”