Vibronic Structure of Electronic Absorption and Fluorescence Spectra of Pyrene in the Complex with Β-Cyclodextrin in the Presence of Nonpolar and Polar Solvents

The feasibility of using pyrene as a fluorescent probe in complexes cyclodextrin-pyrene-analyte in aqueous solutions was studied for several analytes (A) of different polarity. Bands that prove the formation of the complex Py 2 βCD were found for the first time in the UV-VIS spectrum of an aqueous solution of pyrene in the presence of β-cyclodextrin. A characteristic of a fluorescent probe is the ratio I 3 / I 1 in the fluorescence spectrum, where I 3 is the intensity of the third vibronic line at ∼800 cm −1 , and I 1 is the intensity of the 0-0 transition. The value of I 3 / I 1 for Py 2 βCD is highly sensitive to the addition of an analyte with a concentration of several μM/L to the aqueous solution. Dependences of ( I 3 / I 1 )/ C on the function of the dielectric constant ɛ of the analyte f ɛ= (ɛ − 1)/(2ɛ + 1) are divided into two straight lines with different slopes for nonpolar and polar solvents. Energies of insertion of analytes into Py 2 βCD were calculated by the quantumchemical PM3 method. An increase in ( I 3 / I 1 )/ C corresponds to the more thermodynamically stable complex 2APy 2 βCD.