Shedding Light on Highly Emissive 1,4‐Dihydropyrrolo[3,2‐b]pyrrole Derivatives: Synthesis and Aggregate‐Dependent Emission

Abstract

Three tetraaryl‐1,4‐dihydropyrrolo[3,2‐b]pyrrole derivatives containing different number of long alkoxy chains (2, 4 and 6) were synthesized, characterized and applied in Organic Light Emitting Diodes (OLEDs). The compounds showed good emission properties with Photoluminescence Quantum Yields (PLQYs) higher than 80% in solution and 50% in solid state (thin film). The solvatochromism results revealed a pronounced vibronic emission in methylcyclohexane and toluene, characterized by two distinct sharp emission peaks and a small redshift in the following order: methylcyclohexane > toluene > dichloromethane > tetrahydrofuran > acetonitrile. Also, the compounds formed aggregates with redshifted emission, which can be attributed to excimer formation. This phenomenon was observed in solutions containing 90% water and with the concentration variation in methylcyclohexane (MCH). Compounds with a greater number of peripheral chains showed the capacity to keep hexagonal columnar organization in films after fast cooling from liquid state. OLEDs fabricated with these compounds showed turn‐on voltages lower than 4.0 V, with luminance higher than 1400 cd.m2, electroluminescence spectra with Full Width at Half Maximum lower than 70 nm and maximum External Quantum Efficiency between 7.2% and 4.3%. Overall, this shows that the 1,4‐dihydropyrrolo[3,2‐b]pyrrole moiety is promising for applications where luminescence is paramount, as in organic light‐emitting devices