Synthesis and Strong Solvatochromism of Push-Pull Thienylthiazole Boron Complexes.

The solvatochromic behavior of two donor-π bridge-acceptor (D-π-A) compounds based on the 2-(3-boryl-2-thienyl)thiazole π-linker and indandione acceptor moiety are investigated. DFT/TD-DFT calculations were performed in combination with steady-state absorption and emission measurements, along with electrochemical studies, to elucidate the effect of two different strongly electron-donating hydrazonyl units on the solvatochromic and fluorescence behavior of these compounds. The Lippert-Mataga equation was used to estimate the change in dipole moments (Δµ) between ground and excited states based on the measured spectroscopic properties in solvents of varying polarity with the data being supported by theoretical studies. The two asymmetrical D-π-A molecules feature strong solvatochromic shifts in fluorescence of up to ~4300 cm-1 and a concomitant change of the emission color from yellow to red. These changes were accompanied by an increase in Stokes shift to reach values as large as ~5700-5800 cm-1. Quantum yields of ca. 0.75 could be observed for the N,N-dimethylhydrazonyl derivative in nonpolar solvents, which gradually decreased along with increasing solvent polarity, as opposed to the consistently reduced values obtained for the N,N-diphenylhydrazonyl derivative of up to ca. 0.20 in nonpolar solvents. These two push-pull molecules are contrasted with a structurally similar acceptor-π bridge-acceptor (A-π-A) compound.

Temperature-Responsive Luminescent Solar Concentrators: Tuning Energy Transfer in a Liquid Crystalline Matrix.

Temperature-responsive luminescent solar concentrators (LSCs) have been fabricated in which the Förster resonance energy transfer (FRET) between a donor-acceptor pair in a liquid crystalline solvent can be tuned. At room temperatures, the perylene bisimide (PBI) acceptor is aggregated and FRET is inactive; while after heating to a temperature above the isotropic phase of the liquid crystal solvent, the acceptor PBI completely dissolves and FRET is activated. This unusual temperature control over FRET was used to design a color-tunable LSC. The device has been shown to be highly stable towards consecutive heating and cooling cycles, making it an appealing device for harvesting otherwise unused solar energy.

n-Channel Organic Semiconductors Derived from Air-Stable Four-Coordinate Boron Complexes of Substituted Thienylthiazoles.

Three acceptor-π-bridge-acceptor (A-π-A) molecules derived from 2-(3-boryl-2-thienyl)thiazole have been synthesized and thoroughly characterized. Incorporation of a B-N unit into thienylthiazole and attachment of suitable acceptor moieties allowed to obtain ambient-stable A-π-A molecules with low-lying LUMO levels. Their potential for applications in organic electronics was tested in vacuum-deposited organic thin film transistors (OTFT). The OTFT device based on boryl-thienylthiazole and 1,1-dicyanomethylene-3-indanone (DCIND) acceptor moieties showed an electron mobility of ≈1.4×10-2  cm2 V-1 s-1 in air, which is the highest electron mobility reported to date for organoboron small molecules. Conversely, the device employing the malononitrile (MAL) derivative as an active layer did not show any charge transport behavior. As suggested by single crystal X-ray analysis of indandione (IND) and MAL derivatives, the enhanced mobility of IND (and DCIND) in comparison to the MAL molecule can be attributed to the effective two-dimensional π-stacking in the solid state imparted by the acceptor moieties with an extended π-surface.