Long-lived emissions from 4 '-substituted Pt(trpy)Cl+ complexes bearing aryl groups. Influence of orbital parentage

Pt(trpy)Cl+, where trpy denotes 2,2 ' :6 ' ,2 " -terpyridine, is a versatil e binding agent but has a limited photochemistry due to a short excited-sta te lifetime. However, this work shows that the introduction of and substitu ents at the 4 ' position of the trpy ligand drastically alters the picture. For the substituents phenyl, p-methoxyphenyl, 1-naphthyl, 2-naphthyl, 9-ph enanthrenyl, and 1-pyrenyl, the ligand abbrevations are 4 ' -Ph-T, 4 ' -pMe OPh-T, 4 ' -Npl-T, 4 ' Np2-T, 4 ' -Phe9-T, and 4 ' -Pyre1-T, respectively. Techniques utilized include electrochemistry as well as absorption and emis sion spectroscopies, While the lowest energy excited states of Pt(4 ' -Ph-T )Cl+ and the parent complex Pt(trpy)Cl+ exhibit mainly metal-to-ligand char ge-transfer (MLCT) character, the emitting state takes on aryl-to-trpy intr aligand charge-transfer (ILCT) character as the substituents become more el ectron-donating. Studies of Zn(bpy)Cla, its aryl-substitute) analogues, and the free ligands themselves provide information about the relative energie s of participating ILCT and intraligand 3 pi-pi* excited states. Even thoug h the emission energy decreases when larger aryl groups are present, the em ission lifetime increases all the way from 85 ns for Pt(4 ' -Ph-T)Cl+ to 64 ys for Pt(4 ' -Pyre1-T)Cl+. (Data from deoxygenated, room-temperature dich loromethane solution.) Intraligand character appears to dominate in the cas e of Pt(4 ' -Pyre1-T)Cl+, which is unique in the series in that it exhibits singlet and triplet emissions in solution. In aerated solution the complex shows prompt as well as delayed fluorescence Finally, studies in donor med ia establish that the introduction of intraligand character inhibits solven t-induced exciplex quenching.