Efforts toward the synthesis of ESIPT-active anthracene substituted phenols

Phenols containing pendant anthracene groups are known to undergo excited-state intramolecular proton transfer (ESIPT) reactions that cause photoaddition to the anthracene ring across the 9 and 10 positions. This causes bleaching of the anthracene absorption, which makes this compound potentially useful as a contrast enhancement material. The addition of a bulky substituent to the ortho-position of a phenol has been shown to improve the efficiency of ESIPT reactions. In an attempt to both increase the anthracene absorption and increase the reaction quantum yield, we set out to make phenols substituted with two anthracene groups (on the 2 and 6-positions), and one anthracene group (23) and one t-butyl group (22). Efforts toward the syntheses of 22 and 23 involved a Suzuki coupling strategy, although the coupling step has been hampered by competing protodeboronation of the boronic acid, and protodebromination of the aryl halide, likely due to the high degree of steric bulk in the proposed product. While neither 22 nor 23 were synthesized, 15 was synthesized in a very small amount (2.7% yield). UV-Vis spectroscopy was used in addition to 1H and 13C NMR to identify the product as well as to obtain a standard UV spectrum for future comparison. This research can be beneficial to the production of contrast enhancement materials (CEMs) which are used in the production of microelectronics such as microchips.