Toward ultralow-bandgap liquid crystalline semiconductors: Use of triply fused metalloporphyrin trimer-pentamer as extra-large π-extended mesogenic motifs

In contrast with their dimeric homologue, triply fused zinc porphyrin trimer-pentamer, as extra-large π-extended mesogens, assemble into columnar liquid crystals (LCs) when combined with 3,4,5-tri(dodecyloxy)phenyl side groups (3 P _Zn-5 P _Zn, Figure 1). Their LC mesophases develop over a wide temperature range, namely, 41-280 °C (on heating) for 5 P _Zn, and all adopt an oblique columnar geometry, typically seen in columnar LC materials involving strong mesogenic interactions. These LC materials are characterized by their wide light-absorption windows from the entire visible region up to a near infrared (NIR) region. Such ultralow-bandgap LC materials are chemically stable and serve as hole transporters, in which 5 P _Zn gives the largest charge carrier mobility (2.4×10 ^-2 cm V ^-1 s ^-1) among the series. Despite a big dimensional difference, they coassemble without phase separation, in which the resultant LC materials display essentially no deterioration of the intrinsic conducting properties. Low bandgap: Triply fused zinc porphyrin trimer-pentamers serve as extra-large π-extended mesogens for the formation of ultralow bandgap columnar liquid-crystalline (LC) semiconductors with very wide LC mesophase temperature ranges and light-absorption windows (see figure). The mobility of pentramer is roughly one order of magnitude greater than that of dimeric reference.