Stabilizing Pentacene By Cyclopentannulation

Abstract

A new class of stabilized pentacene derivatives with externally fused five‐membered rings are prepared by means of a key palladium‐catalyzed cyclopentannulation step. The target compounds are synthesized by chemical manipulation of a partially saturated 6,13‐dibromopentacene precursor that can be fully aromatized in a final step through a DDQ‐mediated dehydrogenation reaction (DDQ=2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone). The new 1,2,8,9‐tetraaryldicyclopenta[fg,qr]pentacene derivatives have narrow energy gaps of circa 1.2 eV and behave as strong electron acceptors with lowest unoccupied molecular orbital energies between −3.81 and −3.90 eV. Photodegradation studies reveal the new compounds are more photostable than 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐pentacene).

Hysteretic Three-State Redox Interconversion among Zigzag Bisquinodimethanes with Non-fused Benzene Rings and Twisted Tetra-/Dications with [5]/[3]Acenes Exhibiting Near-Infrared Absorptions

“…[n]Acenes are highly attractive molecules because their HOMO/LUMO levels and small band gap can be easily modulated by -extension and the introduction of various substituents or steric strain to the acene core. [1][2][3][4][5][6][7][8][9][10][11] Thus, their optical and electrochemical properties can be finetuned. As a result, [n]acenes are widely used as functional organic materials such as semiconductors, [12][13][14][15] fluorescent probes, [16][17][18] and optoelectronic devices.…”

A twist in the non-slanted H-mers to control π-conjugation in 2-dimensions and optical properties

“…Thioesterification and reduction of 3 gave adamantane-1,3-dimethanethiol (5). Compound 5 was reacted with 2-bromoxylylene dibromide under high dilution conditions to form (AE)-bromo adamantanocyclophane (6). Compound 6 is obtained as a racemic mixture due to planar chirality.…”

“…The synthesis and study of structurally well-defined, monodisperse p-conjugated oligomers of diverse shapes that are conjugated in 2-dimensions provide insights into the impact of molecular shape on the extension of p-conjugation in 2-dimensions. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Also, nanosized 2D-p-conjugated oligomers lend an opportunity to realize unique physical and electronic properties that are unattainable with linearly conjugated oligomers. For example, cruciform-shaped (also reported as X-mers) [3][4][5]20 optically active p-conjugated oligomers developed by the Bunz group and others exhibit spatially non-overlapping frontier molecular orbitals, which bestowed them with remarkable sensory behavior.…”

Polycyclic Hydrocarbons from [4n]Annulenes: Correlation versus Hybridization Forces in the Formation of Diradicaloids

“…Both molecules display electronic absorption spectra with bands at very low energy at 770 nm (with a long absorption tail up to 1000 nm) in 17 and at 680 nm (with tail up to 830 nm) in 18 , which are characteristically weak and broad following the spectral profile pattern expected for antiaromatic non‐alternant molecules. Pentacene homologues of 18 with peripheral 4 n =20 have also been prepared by the Plunkett group [52] . The presence of multiple internal bonds in 17 and 18 (red lines in Scheme 4) promote hybridization energies amounting to E H–L =0.27 and 0.50, respectively, resulting in small diradical characters ( y 0 =0.150 for 17 and y 0 =0.112 for 18 , respectively).…”