Excited State Intramolecular Proton Transfer in π-Expanded Phenazine-Derived Phenols

Abstract

Two previously inaccessible analogs of 10-hydroxybenzo[h]quinoline were prepared via a straightforward strategy comprising the formation of π-expanded phenazines skeleton followed by C-H acetoxylation at position 10. Two bis-phenols possessing C2 and D2 symmetry were obtained in yields of 52% and 15%, respectively. The occurrence of excited state intramolecular proton transfer (ESIPT) was detected in all cases because steady state emission was observed only from the excited keto-tautomer. Additionally, a short-lived, ∼0.1 ps, emission decay was resolved by the femtosecond up-conversion technique at the blue side of the keto-tautomer emission band, 610 nm, and was attributed to the ESIPT, i.e., conversion from enol to keto tautomer. In comparison with the corresponding 10-hydroxybenzo[h]quinoline emissions, the emission spectrum of the π-expanded phenazine analogues were weaker but displayed a characteristic bathochromically shift into NIR region. These phenazine analogues constitute one of largest heterocycles for which ESIPT was unambiguously detected.

Synthesis of a New Series of Organic Solid-State Near-Infrared Emitters: The Role of Crystal Packing and Weak Intermolecular Interactions and Application in Latent Fingerprint Detection

“…Near-infrared (NIR) luminescence materials have attracted considerable interest in recent years because of their increasing demand in areas such as bioimaging, , telecommunications, night-vision equipment, photodynamic therapy, and optoelectronics. − However, the development of novel solid-state NIR emitters is a challenging task. A low band gap is one of the prerequisites for NIR emission, which often necessitates the chromophore to be planar with extended π-conjugation. ,− Such planar conjugated systems often tend to form π–π stacking interactions leading to aggregation-caused quenching (ACQ). ,− Therefore, a careful design of the chromophore avoiding detrimental interactions is extremely important in the development of solid-state NIR emitters. Structural and packing analyses of the chromophore moieties through single-crystal X-ray crystallography may reveal important information useful for the design of new and improved systems.…”

Facile Synthesis of an Organic Solid State Near-Infrared-Emitter with Large Stokes Shift via Excited-State Intramolecular Proton Transfer

“…A pre-requisite for NIR emission is the low band gap, which is often achieved by incorporating extended π-conjugation in the molecular design. 2,8−10 However, such systems often tend to self-assemble through weak-bonding interactions leading to aggregation-caused quenching (ACQ) of fluorescence. 9,11−13 Protection of the NIR chromophore by bulky groups is a well-accepted strategy for preventing the ACQ effect.…”

Composition-dependent nanoelectronics of amido-phenazines: non-volatile RRAM and WORM memory devices

“…Natural phenazine compounds and their synthetic analogues have been detected in the following forms: anti-respiratory secretion 33 ,antibiotic, antitumor, antimalarial and antiparasitic compounds 34 , microorganisms 35 , anticancer prodrug 36 , insecticide 37 , and ruthenium-based DNA-intercalation and aggregate-detector 38 , colorimetric 39 , photophysical 40 , and showed preliminary observation for material application 41 – 43 . Only a limited number of synthetic methods are found in the literature, such as synthesis through functionalization of the phenazines frameworks 41 , RuCl 3 -catalysed cyclization of aromatic azides 44 , coupling of 1,2-diketones with 1,2-diamines 37 , 45 and oxidative coupling of amines 38 .…”