Dual Fluorescence of Fast Blue RR and Fast Violet B: Effects of Solvents and Cyclodextrin Complexation

Abstract

Absorption and steady-state and time-resolved fluorescence spectra of fast blue RR (FBRR) and fast violet B (FVB) were studied in solvents with different polarities and in the presence of α- and β-cyclodextrins (CDs). Dual emission observed in nonpolar solvents suggested that the energy of the intramolecular charge transfer (ICT) state is lower than that of the locally excited state. The normal Stokes-shifted band originated from the locally excited state, and the large Stokes-shifted band was due to the emission from a planar intramolecular charge transfer (PICT) state. The ratio of the PICT emission to the normal emission increased with β-CD concentration, whereas it was constant upon addition of α-CD. This behavior is in accordance with CD-dependent decay times of PICT and normal emissions, indicating the formation of different 1:1 FBRR/CD inclusion complexes. The rise time for the PICT emission increased with β-CD concentration, whereas no rise time was observed in the case of the α-CD complex. The size of the dimethoxyaniline ring suggested that the orientation of FBRR in the β-CD complex was different from that in the α-CD complex. The benzamido moiety of FBRR is deeply encapsulated in the CD cavity, whereas the aniline ring is exposed to the hydrophilic part. Semiempirical quantum-mechanical (ΔE, ΔG, ΔH, ΔS, and HOMO-LUMO) calculations were also carried out to assign the encapsulation of FBRR and FVB.

Guest-Host Inclusion Complex Formation of 2-, 3-, and 4-Aminobenzoic Acids with Native and Modified Cyclodextrins

“…Considering the shape and dimensions of the CDs, ABAs can completely be encapsulated with the β-CD cavity when compared with than α-CD. The distance between 2ABA =H 5 20. These values are less than that the inside β-CD cavity (6.5 Å), but higher than α-CD (5.7Å).…”

“…However, with α-CD/HP-α-CD solutions, the emission intensities of all the ABAs increased. Further, the absorbance and fluorescence intensity changes were different in α-CDs and β-CDs, which indicate all the CDs form different types of inclusion complexes [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].…”

Encapsulation of 4-hydroxy-3-methoxy benzoic acid and 4-hydroxy-3,5-dimethoxy benzoic acid with native and modified cyclodextrins

“…A clear isosbestic point was observed in the absorption spectra and the changes were observed in the absorbance are very small. Further, no changes were observed in the absorbance of these solutions when recorded after 12 h. In general, the existence of an isosbestic point in the absorption spectra is indicative of the formation of well defined 1:1 complex [13][14][15][16][17][18][19][20][21][22][23][24][25]. With the addition of all the four CDs, the increase in absorbance along with a spectral shift indicates the formation of 1:1 HMBA/CD inclusion complexes.…”

“…In addition, CDs can mediate many organic reactions in which CDs represent a good model of mimicking enzymes [6,7] and have molecular recognition property to identify the small differences between compounds [8,9]. Due to the limitations of the experimental methods, in recent times molecular modeling has become very popular in CD chemistry [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

Badania spektroskopowe efektów podwójnej fluorescencji w wybranym związku z grupy 1,3,4-tiadiazoli w rozpuszczalnikach organicznych oraz roztworach wodnych

“…The dual fluorescence effect relies on the appearance of two (or more) bands of fluorescence emission as a result of an excitation with a specific wavelength [22,23]. In 1,3,4-thiadiazoles, such effects may be induced either by pH, solvent polarity, temperature or pressure.…”