Organic electroluminescent materials and devices

A composition comprising, a first compound and a second compound mixed together to form a stable evaporation source for use in a single sublimation crucible of a vacuum thermal evaporation (VTE) process;

• wherein the first compound has a different chemical structure than the second compound;
• wherein the mixture of the first compound and the second compound is capable of functioning as an E-type delayed fluorescent system in an organic light emitting device at room temperature;
• wherein the first compound has an evaporation temperature T1 of 150 to 350° C.;
• wherein the second compound has an evaporation temperature T2 of 150 to 350° C.;
• wherein an absolute value of T1−T2 is less than 20° C.;
• wherein the first compound has a concentration C1 in said mixture and a concentration C2 in a film formed by evaporating the mixture in a vacuum deposition tool at a constant pressure between 1×10−6 Torr to 1λ10−9 Torr, at a 2 Å/sec deposition rate on a surface positioned at a predefined distance away from the mixture being evaporated;
• wherein absolute value of (C1−C2)/C1 is less than 5%;
• wherein the first compound has the formula of D-L-A, where L is a direct bond, A is an electron acceptor group comprising a structure selected from the group consisting of:
• wherein Z1, Z2, Z3, Z4, Z5, Z6, Z7, and Z8 each independently comprise C or N;
• wherein at least two of Z1, Z2, Z3, Z4, Z5, Z6, Z7, and Z8 are N;
• wherein Y1 to Y8 independently comprise C or N;
• wherein A1 to A8 independently comprise C or N;
• wherein J1 and J2 independently comprise C or N;
• wherein L1 to L4 independently comprise C or N;
• wherein X1 is O, S, or NR14;
• wherein R14 is aryl or heteroaryl,
• wherein D is an electron donor group is selected from the group consisting of:
• wherein the second compound (i) comprises at least one chemical group selected from the group consisting of anthracence, naphthylene, phenanthrene, triphenylene, dibenzothiophene, dibenzofuran, dibenzoselenophene, aza-triphenylene, aza-carbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene, or (ii) is selected from the group consisting of: