Figure 2.1. Photochemistry and spectroscopy of an azido DCDHF fluorogen.

(A) Various products resulting from photochemical conversion of an azido DCDHF fluorogen. (B) Absorption curves in ethanol (bubbled with N₂) showing photoactivation of 1 (λ_abs = 424 nm) over time to fluorescent product 2 (λ_abs = 570 nm). Different colored curves represent 0, 10, 90, 150, 240, 300, 480, and 1320 s of illumination by 3.1 mW cm⁻² of diffuse 407-nm light, where the arrows show the direction of increasing time. The sliding isosbestic point may indicate a build-up of reaction intermediates. Dashed line is the absorbance of pure, synthesized 2. (Inset) Dotted line is weak preactivation fluorescence of 1 excited at 594 nm; solid line is strong postactivation fluorescence resulting from exciting 2 at 594 nm, showing > 100-fold turn-on ratio. (Adapted and reproduced with permission from Lord et al.,2008. Copyright 2008 American Chemical Society.)