7-(Dimethylamino)coumarin-3-carbaldehyde and Its Phenylsemicarbazone: TICT Excited State Modulation, Fluorescent H-Aggregates, and Preferential Solvation

Abstract

The photophysical properties of 7-(dimethylamino)coumarin-3-carbaldehyde 3 and its phenylsemicarbazone 4 were investigated in solvents of various polarity and in differing solvent mixtures. The different fluorescent quantum yield (ΦF) behavior of 3 and 4 in highly polar solvents is discussed in terms of Twisted Intramolecular Charge-Tranfer (TICT) state formation and the specific solute-solvent interactions. Because of the weak intermolecular hydrogen bonding ability of both the radiative ICT and nonradiative TICT excited state of 3 and the linear steep decrease in ΦF from a medium to high polarity region, coumarin 3 could be a useful polarity probe for microenvironments containing hydrogen bonding groups. Compared to 3, coumarin 4 exhibits the highest ΦF values in highly polar solvents with strong hydrogen bond acceptor ability. The high quantum yield of fluorescence in DMSO, DMF, and alcohols qualifies coumarin 4 as a laser dye in the given medium, with kF higher than k(nr). Contrary to previous reports that many H-aggregates are nonfluorescent in nature, coumarin 3 forms highly fluorescent H-aggregates in MeOH and EtOH. On the basis of the restrictions of the Kasha-exciton theory model, we assume that the formation of fluorescent H-dimer aggregates of 3 is driven by π(+)-π(-) interactions. To the best of our knowledge, this is the first report on aggregation of coumarin dye in alcoholic solutions. In addition, restrictions in the fitting procedure relating to determination of the solvation number, n, using the Covington-Newman model of preferential solvation and also the solvent nonideality parameter, h', are discussed in this article.

Dissolution of Trihexyltetradecylphosphonium Chloride in Supercritical CO2

“…However, it does appear that the calculated H-aggregate spectrum is more consistent with the measured data with respect to actual peak wavelengths. Although the Kasha model predicts that H-aggregates are non-fluorescent because of forbidden electronic transitions, fluorescent H-aggregates have been reported [73,76,77,85]. Pal and co-workers have discussed this at length for C153.…”

Formation of fluorescent H-aggregates of a cyanine dye in ultrathin film and its effect on energy transfer

“…These types of interactions may be responsible for the imperfect stacking or inclined geometry of Oxa18 molecules in the Haggregate. Also there may be suppression of the nonradiative decay channels due to the increased rigidity of the molecular chain in the π-π stacked aggregate as suggested by Cigáň et al [10].…”

“…However, this rare H -aggregate fluorescence is also observed in other dye types [10][11][12]. The most important and unlikely behavior is seen in case of the dye coumarin 481, where the fluorescence intensity of H -aggregates unexpectedly exceeds the monomer fluorescence intensity [10].…”

“…It is relevant to mention in this context that fluorescence behavior of H -aggregates of some cyanine derivatives have already been reported [6][7][8][9]. However, this rare H -aggregate fluorescence is also observed in other dye types [10][11][12]. The most important and unlikely behavior is seen in case of the dye coumarin 481, where the fluorescence intensity of H -aggregates unexpectedly exceeds the monomer fluorescence intensity [10].…”

Synthesis and Application of a Multifunctional Fluorescent Polymer Based on Coumarin

“…In order to overcome these deficiencies, many methods have been adopted. For instance, the introduction of water-soluble compounds or polymerization (Bangar and Varandajaran 1994;Wagner 2009;Guo et al 2012;Zhang et al 2011a;Cigan et al 2013;Essaidi et al 2013). In this paper, a novel multifunctional fluorescent polymer based on coumarin (MFPC) was synthesized by copolymerization, containing CFM, UVAM, DMC, and AM monomers.…”