W0118: Engineering Crystals for Excited-State Diffraction Studies: Two Polymorphs of 4,4'-dihydroxybenzophenone/4,13-diaza-18-crown-6

The molecule of benzophenone has a long-lived triplet state. However, in its crystal the excitation centers, which are the carbonyl groups, are not well separated, leading to triplet-triplet annihilation at high excitation percentages. Crystals of the complex of 4,4'-dihydroxybenzophenone with 4,13-diaza-18-crown-6 were prepared for use in excited-state diffraction studies [1]. Monoclinic and triclinic polymorphic modifications were obtained. Their structures were solved at 20(2)K with data collected at the X3 beamline at the National Synchrotron Light Source of Brookhaven National Laboratory. The crystallographic information is as follows: P2 ₁/c, a=8.913Å, b=17.501(1)Å, c=17.110(1)Å, (=104.23(, R = 0.044, wR2 = 0.107; and P-1, a=8.620(1)Å, b=10.269(1)Å, c=15.717(1)Å, (=90.59(1)(, (=104.28(1)(, (=111.20(1)(, R=0.037, wR2=0.122. Especially in the triclinic modification, the carbonyl oxygen atoms are found to be widely separated. DSC studies gave a melting point peak at 133.8(C for the monoclinic modification and two peaks at 128.8(C and 133.0(C for the triclinic structure. Room temperature luminescence lifetimes are 44.2(1.2 (s for the monoclinic and 49.2(0.5 (s for the triclinic forms, respectively. The long room-temperature lifetime and the considerable separation of carbonyl groups in the crystals make them promising candidates for excited-state diffraction studies.