Photophysical Properties of the 2-Hydroxytryptanthrin and Its Sodium Salt as Near-infrared Dyes for Fluorescent Imaging

Abstract

2-Hydroxytryptanthrin (T2OH) and its sodium salt (sodium tryptanthrin-2-olate, T2ONa) were synthesized as near-infrared (NIR) dyes for fluorescent imaging. The absorption maxima (λ_a,max) of T2OH under a pH range from 1.3 to 7.2 and from 8.5 to 10.6 were ca. 410 nm and ca. 495 nm, respectively. Moreover, the fluorescence maxima (λ_f,max) were ca. 660 nm regardless of the pH range. T2ONa was water soluble and the λ_f,max were ca. 660 nm in both aprotic and protic solvents.