Synthesis, photophysical and computational studies of two lophine derivatives with electron-rich substituents in the 2-position

An exploration of the photophysical properties of two lophine derivatives with electron-donating groups in the 2-position began with the preparation of compounds 1 and 2 via one-pot reactions in good yields, 83% and 74%, respectively. The absorption spectra of 1 and 2 had bands at approximately 300 nm (epsilon approximate to 25,000-34,000 M-1 cm(-1)), while that of 2 had an additional band at 348 nm (epsilon approximate to 35,600 M-1 cm(-1)). These absorptions were assigned to pi -> pi* transitions. Excitation into the absorption band of 1 at approximately 300 nm produced emission at 387 nm, while excitation into either of the absorption bands of 2 produced emission at 406 nm. Of the two compounds, 2 had the higher quantum yield. The emission spectra of compounds 1 and 2 were slightly blue-shifted at 77 K. Excited state lifetimes for 1 and 2 were short (indicating that the observed emission was fluorescence) at room temperature and 77 K, ranging from 1.1 to 1.8 ns. Computational studies of both compounds 1 and 2 were performed to better understand how their structures relate to their photophysical properties. (C) 2016 Elsevier B.V. All rights reserved.