Organic light-emitting material, device and method

A composition comprising an organic semiconducting material and a triplet-accepting material of formula (I) having a triplet energy level lower than the triplet energy level of the organic semiconducting material:

• wherein each Ar independently represents an optionally substituted aryl or heteroaryl group;
• n is 1-3;
• m in each occurrence is independently 1-5;
• q is 0 or 1;
• each R3 is independently selected from H or a substituent;
• each R4 is independently selected from H or a substituent;
• in the case where R4 is not H, R4 and (Ar)m bound to the same carbon atom may be linked by a direct bond or a divalent group;
• in the case where R3 is not H, R3 independently in each occurrence and (Ar)rn may be linked by a direct bond or a divalent group;
• and adjacent Ar groups may be linked by a divalent group in the case where n or m is at least 2, with the proviso that, in the case where q=0, R3 is not H and is linked to (Ar)n by a direct bond or a divalent group.