Theoretical studies on dimerization reactions of 4, 7-diphenyl-1, 10-phenanthroline (BPhen) and bathocuproine (BCP) in organic semiconductors

The dimerization reactions of 4, 7-diphenyl-1, 10-phenanthroline (BPhen) and bathocuproine (BCP) were studied theoretically. In this work, the molecular geometries, BPhen and BCP monomers, positively charged BPhen and BCP intermediates, and BPhen and BCP dimers were calculated in neutral state at different levels of ab initio methods for the dimerization reactions. The molecular geometries of the BPhen and the BCP monomers and their dimers in their cationic and anionic states were optimized using the B3LYP/6-31G $(d)$ method. The $\pi$ orbitals interactions in the phenyl groups are responsible for the shortening of the C6-N1 and C7-N1 bond distances in BPhen and BCP dimers. The large difference between the reorganization energy components of BCP dimer for hole transport process is due to larger energy required to reorganize C$_5$C$_4$N$_2$C$_6$ and C$_8$C$_1$N$_1$C$_7$ angles. The methyl groups and the phenyl rings act as sterically hindering groups in the BPhen and BCP dimers. In contrast to BPhen dimer where its electron hopping rate is less than BPhen monomer, the magnitude of electron hopping rate of BCP dimer is 12 times higher than BCP monomer.