Light emitting device and production method thereof, and composition for light emitting device and production method thereof

A composition for light emitting device comprising

• a thermally activated delayed fluorescent compound (A) and
• a compound (B) having a condensed hetero ring skeleton (b) containing a boron atom and at least one selected from the group consisting of an oxygen atom, a sulfur atom, a selenium atom, an sp3 carbon atom and a nitrogen atom in the ring, wherein
• said thermally activated delayed fluorescent compound (A) is a compound not having said condensed hetero ring skeleton (b),
• the absolute value (|EB−AA|) of a difference between the energy value (EB) of the maximum peak of the emission spectrum at 25° C. of said compound (B) and the energy value (AA) of a peak at the lowest energy side of the absorption spectrum at 25° C. of said compound (A) is 0.60 eV or less,
• the absolute value ΔEST(A) of a difference between the energy level of the lowest triplet excited state and the energy level of the lowest singlet excited state of said compound (A) is 0.50 eV or less, and
• the absolute value ΔEST(B) of a difference between the energy level of the lowest triplet excited state and the energy level of the lowest singlet excited state of said compound (B) is 0.50 eV or less.

A method for producing a composition for light emitting device, comprising

• a preparation step of preparing a thermally activated delayed fluorescent compound (A) in which the absolute value ΔEST(A) of a difference between the energy level of the lowest triplet excited state and the energy level of the lowest singlet excited state is 0.50 eV or less,
• a sorting step of sorting a compound (B) which is a compound having a condensed hetero ring skeleton (b) containing a boron atom and at least one selected from the group consisting of an oxygen atom, a sulfur atom, a selenium atom, an sp3 carbon atom and a nitrogen atom in the ring and in which the absolute value ΔEST(B) of a difference between the energy level of the lowest triplet excited state and the energy level of the lowest singlet excited state is 0.50 eV or less and the energy value (EB) of the maximum peak of the emission spectrum at 25° C. shows a value with which the absolute value (|EB−AA|) of a difference from the energy value (AA) of a peak at the lowest energy side of the absorption spectrum at 25° C. of said compound (A) is 0.60 eV or less, and
• a production step of mixing the compound (A) prepared in said preparation step and the compound (B) sorted in said sorting step to obtain a composition for light emitting device, wherein
• said thermally activated delayed fluorescent compound (A) is a compound not having said condensed hetero ring skeleton (b).

A method for producing a composition for light emitting device, comprising

• a preparation step of preparing a compound (B) in which the absolute value ΔEST(B) of a difference between the energy level of the lowest triplet excited state and the energy level of the lowest singlet excited state is 0.50 eV or less, and having a condensed hetero ring skeleton (b) containing a boron atom and at least one selected from the group consisting of an oxygen atom, a sulfur atom, a selenium atom, an sp3 carbon atom and a nitrogen atom in the ring,
• a sorting step of sorting a thermally activated delayed fluorescent compound (A) in which the absolute value ΔEST(A) of a difference between the energy level of the lowest triplet excited state and the energy level of the lowest singlet excited state is 0.50 eV or less, and, the energy value (AA) of a peak at the lowest energy side of the absorption spectrum at 25° C. shows a value with which the absolute value (|EB−AA|) of a difference from the energy value (EB) of the maximum peak of the emission spectrum at 25° C. of said compound (B) is 0.60 eV or less, and
• a production step of mixing the compound (B) prepared in said preparation step and said compound (A) sorted in said sorting step to obtain a composition for light emitting device, wherein
• said thermally activated delayed fluorescent compound (A) is a compound not having said condensed hetero ring skeleton (b).