Donor-acceptor type thermally activated delayed fluorescent materials based on imidazo[1,2-f]phenanthridine and analogues

A compound represented by General Formula I or General Formula II:

• wherein:
• each occurrence of Donor represents no substitution or represents a group of Formula A, provided that at least one Donor represents a group of Formula A:
• wherein, in Formula A, * and # represent bonds to adjacent positions on General Formula I or General Formula II;
• each R4 independently represents hydrogen, cyanide, halogen, hydroxy, amino, nitro, thiol, or substituted or unsubstituted C1-C4 alkyl, alkoxy, or aryl;
• or two adjacent groups R4 together form a group of Formula B
• wherein, in Formula B, ‡ and § represent bonds to adjacent positions on Formula A;
• each U1 and U4 independently represents O, S, CRR′, SiRR′, or NAr*, where R and R′ each independently represents hydrogen, cyanide, halogen, hydroxy, amino, nitro, thiol, or optionally substituted C1-C4 alkyl, alkoxy, or aryl, and Ar* represents a substituted phenyl, pyridyl, naphthyl, pyrimidyl, pyridazinyl, pyrazinyl, pyrazolyl, imidazolyl, oxazolyl, or thiazolyl ring, and Ar* is optionally covalently bonded to V2 to form one or more 5-membered or 6-membered rings,
• R1, R2, R3, and R5 each independently represents hydrogen, cyanide, halogen, hydroxy, amino, nitro, thiol, or substituted or unsubstituted C1-C4 alkyl, alkoxy, or aryl, and
• V2 represents N or substituted or unsubstituted C,
• each X1, X2, X3, X4, X5, X6, X7, X8, X9, X10, X11, X12, X13, X14, X15, X16, X17, and X18 independently represents substituted or unsubstituted C, N, Si, O, or S, valency permitting, and
• each n is independently an integer as permitted by valence.