Fluorescence phenomena in nerve-labeling styryl-type dyes

• Synthesized and investigated photophysical properties of several substituted styryl type dyes d1–d15.
• Three dyes d7, d9 and d10 showed good fluorescent properties and maintained drug-like binding property.
• Observed an unusual dual emission behavior with two distinct ground state conformers that could individually be excited.
• Observed an anomalous emission behavior on dye systems d7 and d8 the amino-derivative d7 showed a dual emission characteristic in the polar medium, while the N,N-dimethyl derivative d8 did not.
• Interestingly, when compound d7 was injected into a mouse and the dye bound to nerves were excited by either 405 nm or 447 nm laser, a wavelength dependent emission described above was observed similar to fluorescence in DMSO.
• In vivo fluorescence imaging studies in rodents using small animal multispectral imaging instrument and the dual-mode laparoscopic instrument developed in-house.

Several classes of diversely substituted styryl type dyes have been synthesized with the goal of extending their expected fluorescent properties as much toward red as possible given the constraint that they maintain drug-like properties and retain high affinity binding to their biological target. We report on the synthesis, optical properties of a series of styryl dyes (d1–d14), and the anomalous photophysical behavior of several of these donor–acceptor pairs separated by long conjugated π-systems (d7–d10). We further describe an unusual dual emission behavior with two distinct ground state conformers which could be individually excited to locally excited (LE) and twisted intramolecular charge transfer (TICT) excited state in push–pull dye systems (d7, d9 and d10). Additionally, unexpected emission behavior in dye systems d7 and d8 wherein the amino-derivative d7 displayed a dual emission in polar medium while the N,N-dimethyl derivative d8 and other methylated derivatives d12–d14 showed only LE emission but did not show any TICT emission. Based on photophysical and nerve binding studies, we down selected compounds that exhibited the most robust fluorescent staining of nerve tissue sections. These dyes (d7, d9, and d10) were subsequently selected for in vivo fluorescence imaging studies in rodents using the small animal multispectral imaging instrument and the dual-mode laparoscopic instrument developed in-house.

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