A compound having a structure of Formula I:

##STR00001##

is provided. In the structure of Formula I, each one of X.sup.1 to X.sup.16 is independently CR.sup.X or N; each R.sup.X and R are independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, carbazole, azacarbazole, dibenzofuran, dibenzothiophene, dibenzoselenophene, azadibenzofuran, azadibenzothiophene, azadibenzoselenophene, triphenylene, azatriphenylene, and combinations thereof; and any adjacent R.sup.X can join to form fused or unfused rings. Formulations and devices, such as an OLEDs, that include the compound containing a structure of Formula I are also described.

The present invention relates to inhibitors of zinc-dependent histone deacetylases (HDACs) useful in the treatment of diseases or disorders associated with HDAC6, having a Formulae I or Formula II: ##STR00001## where R, L, X.sup.1, X.sup.2, X.sup.3, X.sup.4, X.sup.5, Y.sup.1, Y.sup.2, Y.sup.3, and Y.sup.4 are described herein.