Full Length Article Structure and aggregation of β-cyclodextrin–pyrene–analyte supramolecular sensor: Absorption/emission spectra and simulations Vitaly G. Avakyan a,n , Valery B. Nazarov b , Alexei V. Odinokov a , Alexander V. Koshkin c , Mikhail V. Alfimov a a Photochemistry Center, Russian Academy of Sciences, ul. Novatorov 7a, Moscow,119421 Russian Federation b Institute for Problems in Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432 Russian Federation c National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoye sh. 31, Moscow,115409 Russian Federation article info Article history: Received 20 August 2015 Received in revised form 18 August 2016 Accepted 19 August 2016 Available online 31 August 2016 Keywords: Aggregates of pyrene–β-cyclodextrin inclusion complex Electronic absorption and fluorescence spectra Pyrene as a fluorescent probe Intensity ratios of vibronic lines of pyrene Molecular dynamics simulation Quantum-chemical modeling abstract The possibility of using pyrene as a fluorescent probe in a model chemosensor composed of β-cyclo- dextrin–pyrene (Py–βCD) complex in aqueous solution was studied in the presence of several analytes (A) of different polarity. Absorption bands that prove the formation of the aggregated Py–βCD complex were found in the UV–VIS spectra of aqueous solution of pyrene with added βCD. The aggregate size as measured by dynamic light scattering was found to have a value of 3.2–3.6 nm. The aggregate was identified as a 1:2 complex of Py with βCD (Py@2βCD) surrounded by two empty βCD molecules. The ratio I 3 /I 1 of intensity I 3 of the third vibronic band at 26,000 cm 1 in the fluorescence spectrum to intensity I 1 of the 0–0 transition at 26,800 cm 1 was used as an analytical characteristic of the fluorescent probe. The value of I 3 /I 1 for Py@2βCD is highly sensitive to the presence of several μM of analyte in aqueous solution, and this value is markedly higher than that for pyrene in solution. & 2016 Elsevier B.V. All rights reserved. 1. Introduction Development of optical methods for reliable recognition and detection of environmentally toxic compounds is an important problem. The host–guest chemistry is a promising approach to chemical sensing and environmental monitoring. Among various hosts, cyclodextrins (CDs) are attractive for designing supramole- cular recognition system because they have hydrophobic cavities of nanoscale size that enable them to adsorb various guest mole- cules from aqueous solution [1]. Cyclodextrin molecules, in parti- cular, β-cyclodextrin (βCD), are known [1] to have a shape of truncated conical basket consisting of seven α-D-glucopyranose moieties bound by 1–4 glycoside bonds and a hydrophobic cavity with a hydrophilic exterior. βCD is widely known to form guest– host inclusion complexes with organic compounds in aqueous solution [1]. The stoichiometry of such complexes, βCD/substrate, as determined by absorption/emission spectroscopy, often seems to be rather simple, e.g. 1:1 [1], 2:1 [2], 2:2 [3] or 1:1:1 [4] (where the third number corresponds to molar content of the third component inserted into 1:1 or 2:2 complex). However, such a simple notion about the structure CD com- plexes, when a lipophilic moiety of a hydrophobic molecule enters the hydrophobic cavity of the CD molecule, is gradually replaced by a more complicate model, according to which individual CD molecules, complexes, and complex aggregates coexist in aqueous solution [5]. Previously, the investigation on the structure and fluorescence spectra of naphthalene (Nph)–βCD inclusion com- plexes showed that a fluorescent excimer particle exists in sub- micron aggregates. The appearance of the excimer fluorescence indicated the presence of two naphthalene molecules oriented parallel to each other in such particles and, hence, the stoichio- metry for this Nph–βCD complex can be expected to be 2:2, 2Nph@2βCD [3]. Although the tendency of cyclodextins, and especially βCD [6], to spontaneous aggregation was reported [7], we proposed that adding organic substrate would promote aggregation. This idea has been worked out further [8]. Light scattering measurements revealed that the size distribution of the self-assembled nano- particles varies between 1.5 and 60–120 nm and the thermo- dynamic parameters of the spontaneous self-assembly of βCD in the aqueous solution were found as Δ agg G° ¼  16.31 kJ mol –1 , Δ agg H° ¼  26.48 kJ mol –1 , and TΔ agg S° ¼  10.53 kJ mol –1 at 298.15 K. It has also been shown that the guest molecules act as Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2016.08.051 0022-2313/& 2016 Elsevier B.V. All rights reserved. n Corresponding author. E-mail addresses: avak@photonics.ru, boyev@mail.ru (V.G. Avakyan). Journal of Luminescence 180 (2016) 328–340