Organic electroluminescent materials and devices

A compound comprising a structure of Formula I,

• wherein:
• RW has a structure of Formula II,
• where at least two RE substituents are joined to form a 5-, 6-, 7-, 8-, 9-, or 10-membered carbocyclic or heterocyclic ring;
• each of X1 to X11 is independently C or N with at least two adjacent of X1 to X5 being C;
• each of Z1, Z2, and Z3 is independently C or N;
• M is Pd or Pt;
• each of moiety A, moiety B, moiety C, and moiety D is independently a monocyclic ring or a polycyclic fused ring system, wherein the monocyclic ring or each ring of the polycyclic fused ring system is independently a 5-membered or 6-membered carbocyclic or heterocyclic ring;
• each of L1 and L2 is independently selected from the group consisting of a direct bond, BR, BRR′, NR, PR, P(O)R, O, S, Se, C═O, C═S, C═Se, C═NR′, C═CR′R″, S═O, SO2, CR, CRR′, SiRR′, GeRR′;
• each of RA, RB, RC, RD, and RE independently represents mono to the maximum allowable substitutions, or no substitutions;
• each of R, R′, RA, RB, RC, RD, RE, RE′, and RE″ is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, boryl, arylalkyl, alkoxy, aryloxy, amino, silyl, germyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, selenyl, and combinations thereof;
• and
• any two substituents may be joined or fused to form a ring, with the following provisos:
• (1) RW does not comprise
• wherein in L is a
• direct bond or is absent, and wherein X is selected from the group consisting of BR, BRR′, NR, PR, P(O)R, O, S, Se, C═O, C═S, C═Se, C═NR′, C═CR′R″, S═O, SO2, CRR′, SiRR′, GeRR′;
• (2) if a combination of moiety A and RW comprises a structure
• and two RE substituents are joined to form a 6-membered carbocyclic ring, then (i) the 6-membered carbocyclic ring is substituted, (ii) at least one additional RE is not hydrogen, or (iii) both condition (i) and condition (ii) are true;
• and
• (3) if a combination of moiety A and RW comprises a structure
• and one of RE′ or RE″ is H, then the other one of RE′ or RE″ is not tert-butyl, —C6H5, or —Si(CH3)3;
• (4) if RW comprises
• then at least one RE is a non-hydrogen substituent.