Indolizine-Cyanine Dyes: Near Infrared Emissive Cyanine Dyes with Increased Stokes Shifts

Abstract

Molecular engineering strategies designed to red-shift cyanine dye absorptions and emissions further into the near-infrared (NIR) spectral region are explored. Through the use of a novel donor group, indolizine, with varying cyanine bridge lengths, dye absorptions and emissions, were shifted deeper into the NIR region than common indoline-cyanines. Stokes shifts resulting from intramolecular steric interactions of up to ∼60 nm in many cases were observed and explained computationally. Molecular brightnesses of up to 5800 deep into the NIR region were observed. Structure–property relationships are explored for the six indolizine-cyanine dyes with varying cyanine bridge length and indolizine substituents showing broad absorption and emission tunability. The dyes are characterized by crystallography, and the photophysical properties are probed by varying solvent for absorption and emission studies. Computational data show involvement of the entire indolizine π-system during light absorption, which suggests these systems can be tunable even further into the NIR region through select derivatizations.

Structural investigation of methyl 3-(4-fluorobenzoyl)-7-methyl-2-phenylindolizine-1-carboxylate, an inhibitory drug towards Mycobacterium tuberculosis

“…Out of the 39 hits for unsubstituted phenyl rings attached to indolizine, the majority of entries gave reports of varied synthetic procedures and methodologies to obtain these compounds, underlining their importance. The nearinfrared emissive properties of KIVLIN, KIVLOT, KIVLUZ (Gayton et al, 2019) and KENFAN (McNamara et al, 2017) have also been reported. Structural details of compounds such as CAJTAI (Aslanov et al, 1983), EMUTOV (Liu, et al, 2003), FEDQAH (Liu, et al, 2005), GIYLOP (Sonnenschein & Schneider, 1997), ODEFIN (Qian et al, 2006), PNOIZA, PNOIZB, PNOIZE, PNOIZF (Tafeenkov & Aslanov, 1980), ROLKIM (Tafeenkov & Au, 1996) and TIGXOX (Liu, et al, 2007) have also been deposited.…”

Microwave-Assisted Synthesis of Fluorescent Pyrido[2,3-b]indolizines from Alkylpyridinium Salts and Enaminones

“…Indolizines, and in particular the annulated ones, are frequently found to exhibit useful biological [ 1 , 2 , 3 , 4 , 5 , 6 ] and optical properties [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. The synthesis of indolizines usually relies on the reactivity of pyridinium ylides, which can undergo cycloaddition reactions with alkenes [ 15 , 16 , 17 , 18 ] or alkynes [ 19 , 20 , 21 , 22 , 23 ].…”

Highly Fluorescent Pyrido[2,3‐b]indolizine‐10‐Carbonitriles through Pseudo Three‐Component Reactions of N‐(Cyanomethyl)pyridinium Salts

“…Domino and multicomponent reactions allow rapid and efficient construction of molecular complexity; they are widely used for the synthesis of natural products and analogues,, pharmaceutical substances, functional materials,, macrocyclizations, Employing these tools for the preparation of fluorophores and electrophores emerged as a useful technique, enabling fast creation of numerous scaffolds with diverse structure and needful properties. Indolizines are indeed sought‐for heterocycles,, which have various applications as biologically active compounds, dyes, molecular probes and sensors . They are also well‐known fluorophores, with some recent examples of multicomponent syntheses .…”