Delayed fluorescence compound and organic electroluminescent device using the same

A delayed fluorescence compound of formula (1):

• wherein X is O, S, or Se;
• Y1-Y8 are each independently a nitrogen atom or CR;
• R, R1, and R2 are each independently selected from the group consisting of a hydrogen atom, a halide, a nitro, a pyridine, a pyrazine, a pyrimidine, a pyridazine, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 1 to 30 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms;
• L represents formula (2):
• n is 0 or 1;
• and Z is selected from formulas (3)-(7):
• and
• wherein R3 to R10 are each independently selected from the group consisting of a hydrogen atom, a halide, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, and a substituted or unsubstituted aralkyl group having 6 to 30 carbon atoms;
• Y2 and Y3 are optionally connected to each other to form an aromatic or heteroaromatic ring;
• and Y6 and Y7 are optionally connected to each other to form an aromatic or heteroaromatic ring.