Fluorescence enhancement of cyanine/hemicyanine dyes with adamantane as an auxochrome through host-guest inclusion with methylated cyclodextrin in water

Fluorescence of cyanine dyes is often quenched in aqueous solution, limiting their application in water or biological system. In this work, a novel strategy of host-guest interaction based on cyanine derivatives containing auxochromes was proposed to enhance fluorescence in aqueous solution and cell imaging. By using the host (methylated β-cyclodextrin, M-β-CD) to inclusion and suppress the TICT effect of the dye, the fluorescence was significantly enhanced at lower host concentration. Cyanine and hemicyanine dyes (Ad-NH-1a, Ad-NH-1b and Ad-NH-2) with adamantyl group as auxochrome were designed and prepared by using host-guest complexation to inhibit the TICT effect of dyes, thus realizing the purpose of significantly enhancing the fluorescence of dyes at lower concentration. After adding M-β-CD, the fluorescence quantum yields of these dyes increased to 15.9 %, 21.8 %, and 6.08 %, respectively. In comparison, the fluorescence quantum yield of the dyes Ad-CONH-1 and Ad-CONH-2 containing adamantyl groups, increased only modestly from 1.78 to 2.83 times. Encouraged by these satisfactory results, further cell experiments were conducted with Ad-NH-1a, Ad-NH-1b, and Ad-NH-2. The experiment showed that adding a lower concentration of M-β-CD significantly reduced the clear imaging dosage of the probe (0.3 μM) without altering the organelle targeting of the probes.