β-Isoindigo-azaDIPYs: Fully Conjugated Hybrid Systems with Broad Absorption in the Visible Region

A one-step synthetic pathway for the preparation of fully conjugated β-isoindigo-azaDIPY hybrid chromophores comprised of β-isoindigo and azadipyrromethene moieties is reported. The target compounds were characterized by spectroscopic, crystallographic, and theoretical methods and show unprecedented broad absorption across the visible region of the electromagnetic spectrum. The X-ray crystal structure of the octa(n-butyl)-β-isoindigo-azaDIPY derivative revealed that a trans-configuration of the β-isoindigo fragment accompanies a planar conjugated core.

Environmentally Benign Route for Scalable Preparation of 1-Imino-3-thioisoindolines-The Key Building Blocks for the Synthesis of Dithio- and Diamino-β-isoindigo Derivatives

A one-step, gram-scale protocol for the preparation of 1-imino-3-thioisoindolines and a novel one-pot two-step methodology of the synthesis of dithio- or diamino-β-isoindigo derivatives starting from phthalonitriles and sodium hydrosulfide in an aprotic dipolar solvent have been developed. It was demonstrated that the electronic properties of the substituent(s) in the phthalonitrile core play a critical role in β-isoindigo synthesis resulting either in the selective formation of dithio- or diamino-β-isoindigo chromophores. The N-acylated 1-imino-3-thioisoindolines can be used for the direct, easily scalable, and chromatography-free procedure for the preparation of a new class of N,N'-diacylamino-β-isoindigoid compounds. Properties of the monomeric as well as J-aggregated forms of dithio- and diamino-β-isoindigo were probed by the absorption and fluorescence spectroscopies. It was demonstrated that the tetracyano-diamino-β-isoindigo 3f can form a J-aggregate that absorbs at 793 nm and fluoresces at 824 nm. This aggregate is stable in N,N-dimethylformamide solution; however, it slowly dissociates in tetrahydrofuran or under sonication conditions. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were employed to elucidate the electronic structures, spectroscopic properties, and aggregation of new dithio- and diamino-β-isoindigo derivatives.