In addition to their use as colorants in food and cosmetics, various natural dyes possess photophysical properties that could enable their use as modular building blocks for preparing eco-friendly and non-toxic chromophores. Among the natural pigments, guaiazulene holds great potential due to its unique optical and electronic properties. Thus, in order to explore and understand the properties of guaiazulene-containing chromophores, a series of 4-styrylguaiazulenes 3a-l were prepared by condensation of the C-4 methyl group of naturally-occurring guaiazulene 1 with various aromatic carboxaldehydes 2a-l. Treatment of these analogs 3a-l with a strong acid protonates the electron-rich C-3 position and reveals a reversible halochromic behavior where the optical energy gap responds predictably to the electron-donor strength and the degree of π-conjugation. Additionally, acid-doping is accompanied by efficient fluorescence switch-on, where 3e(H+) and 3g(H+) exhibited considerably higher fluorescence quantum yields than the neutral precursor. These properties facilitated the design of a new non-erasable 3D fluorescence readout (permanent or write-once read-many, WORM) system, which is comprised of a switch-on fluorescent guaiazulene-containing chromophore 3e and a commercially available iodonium photo-acid generator (PAG) in thin polymethyl methacrylate (PMMA) films.
All Science Journal Classification (ASJC) codes
- Materials Chemistry