Rational Molecular Design of Azaacene-Based Narrowband Green-Emitting Fluorophores: Modulation of Spectral Bandwidth and Vibronic Transitions.

A series of green-emitting fluorophores based on a tetra-azaacene core is synthesized by introducing nitrile substituents at different positions. Their molecular structure-optical property relationship [i.e., vibronic transitions in photoluminescence (PL) and electroluminescence (EL) spectra] is investigated to obtain a sharp emission where the vibronic peak ν0-0 should be intensified by suppressing ν0-n (n = 1, 2, 3...) transitions. The intensity ratios (I0-1/I0-0) of the ν0-1 and ν0-0 vibronic transitions in the PL spectra of DBBNP, DBBNP2CN1, and DBBNP2CN2 in hexane are 1.13, 0.80, and 0.67, respectively. Theoretical calculations explain that the CN substitution at positions 8 and 13 in DBBNP2CN2 induces a uniform charge distribution and reduces the Huang-Rhys factors (HRFs) of the vibrational normal modes coupled to the electronic transition. The organic light-emitting diode (OLED) fabricated with DBBNP2CN2 shows a narrower green EL emission at 518 nm with a smaller bandwidth (50 nm) than those of devices adopting DBBNP or DBBNP2CN1. The careful modification of the molecular structures and positions of substituents enables us to reduce the HRFs of vibrations to achieve a narrow emission bandwidth with decreased I0-1/I0-0, which suggests a design strategy to develop narrowband organic fluorophores to improve the color purity for wide-gamut OLED displays.

Highly sensitive phototransistor with crystalline microribbons from new π-extended pyrene derivative via solution-phase self-assembly.

A new pyrene-cored π-conjugated molecule has been synthesized through Sonogashira coupling reaction. The single-crystalline microribbon-based FET exhibited the highest mobility of 0.7 cm(2) V(-1) s(-1) (I(on)/I(off) > 10(6)). Single-crystalline microribbons were employed to operate in an organic phototransistor (OPT) under very low light intensity (I = 5.6 µW cm(-2)).

Semiconducting 2,6,9,10-tetrakis(phenylethynyl)anthracene derivatives: effect of substitution positions on molecular energies.

2,6-Bis((4-hexylphenyl)ethynyl)-9,10-bis(phenylethynyl)anthracene, 4, and 9,10-bis((4-hexylphenyl)ethynyl)-2,6-bis (phenyl ethynyl)anthracene, 5, have been synthesized to study their electronic and photophysical properties. It should be noted that the difference between these compounds is the substitution position of 1-ethynyl-4-hexylbenzene groups into an anthracene ring. In particular, substitution in the 9,10-positions of the anthracene ring enhanced J-aggregated intermolecular interactions. Since 5 has a lower bandgap energy and more compact film morphology, it exhibited higher hole mobility (∼0.27 cm(2) V(-1) s(-1)) in thin-film transistor devices.

High-mobility anthracene-based X-shaped conjugated molecules for thin film transistors.

New anthracene-based X-shaped conjugated molecules and for use as highly soluble p-type organic semiconductors were developed and exhibited large field-effect mobilities of 0.04 cm(2) V(-1) s(-1) (I(on)/I(off) = 2.8 x 10(5)) and 0.24 cm(2) V(-1) s(-1) (I(on)/I(off) = 5.4 x 10(6)) for devices of and , respectively.