Synthesis and electroluminescence of efficient blue fluorescent molecules based on isomers of phenanthroimidazole and pyrene

Isomers provide diverse opportunities for the structural characteristics of organic compounds. The distinct properties of isomers are inherently influenced by their molecular structures, making the study of the relationship between structure and properties an important area of research. Two structural isomers were prepared in this work through the attachment of modified pyrene fluorophores to phenanthroimidazole's N1 site using varied connection sites. These two stable isomers were synthesized through straightforward “one-pot” reaction followed by a Suzuki-Miyaura coupling reaction, involving both meta-linked and para-linked mode towards the pyrene moiety to the phenyl group at the N1 position of phenanthroimidazole. The effect of different molecular configuration of the isomers on the photophysical property, theoretical calculation, thermal property, and electrical property was investigated, showing that twisted conformation may effectively limit the degree of molecular conjugation, thereby reducing the red-shift to maintain deep blue emission. Thus, the non-doped OLED based on m-PPI-PyP-PC showed minimal driving voltage requirement of 2.9 V and demonstrated steady deep blue emission with a Commission International de l’Eclairage (CIE_y) coordinate of 0.078. This study introduces a feasible approach for designing and synthesizing blue fluorophores based on phenanthroimidazole and pyrene as key structural components.