In an embodiment, ring CY2 may be a benzimidazole group, a benzoxazole group, or a benzothiazole group, and ring CY1, ring CY3, and ring CY4 may each independently be a benzene group, a naphthalene group, an anthracene group, a phenanthrene group, a triphenylene group, a pyrene group, a chrysene group, a cyclopentadiene group, a 1,2,3,4-tetrahydronaphthalene group, a fluorene group, a carbazole group, a dibenzofuran group, a dibenzothiophene group, a dibenzosilole group, an azafluorene group, an azacarbazole group, an azadibenzofuran group, an azadibenzothiophene group, an azadibenzosilole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a phenanthroline group, a cinnoline group, a phthalazine group, a 5,6,7,8-tetrahydroisoquinoline group, a 5,6,7,8-tetrahydroquinoline group, a 5,6,7,8-tetrahydrophthalazine group, and a 5,6,7,8-tetrahydrocinnoline group.
In one or more embodiments, each of ring CY1 and ring CY3 may be a benzene ring, and each of ring CY2 and ring CY4 may be a pyridine ring.
T1 in Formula 1 may be a single bond, a double bond, *—N(R51)—*′, *—B(R51)—*′, *—P(R51)—*′, *—C(R51)(R52)—*′, *—Si(R51)(R52)—*′, *—Ge(R51)(R52)—*′, *—S—*, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O)2—*′, *—C(R51)═*′, *═C(R51)—*′, *—C(R51)═C(R52)—*′, *—C(═S)—*′, or *—C≡C—*′,