Solvent-Free Synthesis of 2,5Bis((dimethylamino)methylene)cyclopentanone

Available protocols for the synthesis of ketocyanine dyes precursor 2,5bis((dimethylamino)methylene)cyclopentanone are not straightforward and the reported yields are low to moderate. The important feature in the synthesis of this product through organocatalyzed condensation of cyclopentanone and N,N-Dimethylformamide dimethyl acetal is the removal of methanol produced during the reaction. By studying the reaction profile, in particular the selectivity for the formation of mono- and bis-condensation products, a high yield of the desired product can be obtained through an operationally simple and solvent-free protocol.

Modification of Spectral Behavior of Ketocyanine Dyes by Silver Nanoparticles of Different Sizes

The spectral behavior of two ketocyanine dyes 2,5-di[(E)-1-(4-dimethylaminophenyl) methylidine]-1-cyclopentanone(2,5-DMAPMC) and 2,5-di[(E)-1-(4-diethylaminophenyl) methylidine]-1-cyclopentanone (2,5-DEAPMC) is investigated in the presence of silver nanoparticles (AgNPs) of sizes 32[Formula: see text]nm, 52[Formula: see text]nm and 60[Formula: see text]nm using absorption and fluorescence spectroscopy. The absorption spectral changes of dyes with the addition of AgNPs of different sizes suggest their possible interaction with AgNPs. Fluorescence quenching has been observed for both the dyes with the addition of AgNPs of all the sizes. The possible quenching mechanisms including energy transfer and electron transfer are discussed. The fluorescence quenching rate parameter is found to increase with increase in the size of AgNPs and is explained based on the varying ability of silver AgNPs of different sizes to accommodate dye molecules. The effect of functional groups on quenching rate parameters is also discussed.

Ketocyanine dyes: impact of conjugation length on optical absorption and third-order polarizabilities

Structure–property relationships are proposed for tuning the optical absorption of ketocyanine dyes and to obtain large negative third-order polarizabilities.