Introduction of various substitutions to the methine bridge of heptamethine cyanine dyes Via substituted dianil linkers

Abstract

The unique optical properties of cyanine dyes have prompted their use in numerous applications. Heptamethine cyanines are commonly modified on the methine bridge after synthesis of a meso-chlorine containing cyanine. Herein, a series of heptamethine cyanines containing modified methine bridges were synthesized using substituted dianil linkers. Their optical properties including, molar absorptivity, fluorescence, and quantum yield were measured as well as their hydrophobic effects in polar buffer solution. It was shown that dyes containing cyclopentene in the methine bridge or a phenyl ring in the meso position display increased molar absorptivity while the increased flexibility of the dye containing a cycloheptene in the methine bridge prevented fluorescence.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

“… 1524 The individual contributions of each of these modifications have not yet been determined. In principle, the flexibility of the synthesis 1536 − 1538 and post-synthetic functionalization 1494 , 1531 , 1539 , 1540 , 1510 of cyanines enables useful structural modifications of the bridge or terminal heterocycles, providing considerable scope for modulation of their spectroscopic and photoreaction properties.…”

Explorations into the Effect of meso‐Substituents in Tricarbocyanine Dyes: A Path to Diverse Biomolecular Probes and Materials

“…A meso ‐Cl cyclohexene motif was reported to offer the highest molecular brightness, compared to the dyes featuring cyclopentene and cycloheptene motifs [6b] . The molecular brightness for the cyclopentene derivative was found to be marginally lower and the cycloheptene derivative was found not to be fluorescent.…”

“…The main synthetic strategy for the rigidification of the polymethine chain is the use of a conjugated dialdehyde containing a cyclic motif. These are typically obtained from a double Vilsmeier–Haack‐type reaction involving a cyclic ketone, such as cyclopentanone, cyclohexanone, or cycloheptanone [6b, 8] . In the course of this reaction, the ketone is 1,3‐bisformylated and the oxygen substituent is substituted by a chloride.…”

“…Using phosphoryl bromide, rather than phosphoryl chloride, yields the respective meso ‐Br derivatives [8b] . Another route to access the dialdehydes is by employing 1‐substituted cyclohexenes as the starting materials [6b] …”

“…While absorption maxima are similar for the cyclohexene and cycloheptene derivatives, cyclopentene derivatives display a bathochromic shift (ca. 20 nm) [6b, 8c] . More importantly, the nature of the meso ‐heteroatom at the center of the cyanine polymethine chains has been the focus of numerous studies investigating the routes to substitution and the effect of this substituent on the photophysical properties of the resulting dye.…”