Preparation and photophysical properties of quinazoline-based fluorophores

Abstract

The donor-acceptor design is a classic method of synthesizing new fluorescent molecules. In this study, a series of new fluorescent compounds (1-10) were synthesized based on 2-(3,5-bis(trifluoromethyl)phenyl)-quinazoline acceptor and various amino donors. The fluorescent emissions of 1-10 cover the spectrum from 414 nm to 597 nm in cyclohexane solutions with various amino donors on 4- or 7-positions of quinazoline. Ultimately, compounds 1 and 2 presented the highest photoluminescence quantum yield (QY) over 80%, while compound 10 provided the largest Stokes shift (161 nm) in cyclohexane. Most of them have strong emissions in aggregated states such as in nanoparticles, in powders, in crystals and in films. Mechanochromic properties were observed for compounds 1, 2, 4 and 7. Furthermore, blue OLEDs were fabricated by using compound 2 or 7 as the active layer.

Scheme 1. Key intermediates A, B and compounds 1–10.

Fig. 1. (a) Absorptions and normalized emissions of 1–5 in cyclohexanes; (b) absorptions and normalized emissions of 6–10 in cyclohexanes.

Fig. 2. (a) Absorptions and (b) rainbow emissions of 1 in various solvents.

Fig. 3. (a) 3D emissions of 2, (b) DLS (f_w = 90%, 95%) of 2 and (c) TEM images of 2 (95%).

Fig. 4. (a) Powder emission spectra of 1–5; (b) powder emission spectra of 6–9; (c) colorful powders of 1–10 under UV light.

Fig. 5. Single crystal structures of 1–4: (a) monomeric structure; (b) dimeric structures; (c) tetrameric structures and (d) CLSM images under 405 nm laser of 1–4.

Fig. 6. Mechanochromic property of compounds 2 and 4; (a) normalized emission spectra; (b) emission cycles.

Fig. 7. (a) HOMO/LUMO orbitals calculated by Gaussian (DFT using the B3LYP functional and the 6-31G(d) basis set). (b) Energy gaps (HOMO/LUMO) from theoretical calculation, UV observation and CV versus compounds 1–10.