Russian Chemical Bulletin, International Edition, Vol. 67, No. 12, pp. 2266—2270, December, 2018 2266 Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2266—2270, December, 2018. 1066-5285/18/6712-2266 © 2018 Springer Science+Business Media, Inc. Photochromic transformations of amphiphilic spiropyran in acetonitrile solutions and at the air/water interface* D. A. Ivakhnenko, a,b A. V. Shokurov, a G. V. Lyubimova, c N. L. Zaichenko, c V. V. Arslanov, a and O. A. Raitman a a A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Build. 4, 31 Leninsky prosp., 119071 Moscow, Russian Federation. E-mail: pcss_lab@mail.ru b Mendeleev University of Chemical Technology of Russia, 9 Miusskaya pl., 125047 Moscow, Russian Federation c Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 ul. Kosygina, 119991 Moscow, Russian Federation The results of a study of the photochromic properties of 1´-hexadecyl–3´,3´-dimethyl-6- nitro-1´,3´-dihydrospiro[chromene–2,2´-indole] (SP) are presented. The kinetic characteris- tics of photophysical processes occurring in acetonitrile solution of SP upon irradiation with UV light and during dark relaxation are determined. It is shown that spiropyran modified at the nitrogen atom by a long-chain hydrocarbon radical exhibits photochromic properties in the dissolved state, with the rate of the direct photocoloration exceeding the rate of dark relaxation by an order of magnitude. Comparative studies of SP photoreaction in dissolved and 2D states are carried out. The obtained results open up broad prospects for application of such photo- chromes in thin-film devices obtained using the Langmuir monolayer technique. Key words: spiropyrans, photochromism, amphiphilic compounds, Langmuir monolayers. Spiropyrans are one of the most important classes of photochromic compounds 1—3 and form the basis for de- veloping of various types of optically active materials. They are of interest for numerous areas of modern photo and molecular electronics and can be used in information recording devices and for optical signal processing, 1,4,5 in holography, 6,7 systems for the large scale information displays, 8 medicine, 9 sensorics, 10 etc. The unquestionable advantages of spiropyran photochromes are a high photo- coloration efciency, a considerable spectral separation of photo-switched isomers, and the possibility of fine-tuning various characteristics of the photochromic equilibrium by altering the molecular structure. 1,2 Most practical applications require the photochromic molecules to be highly organized on the working surface of a device. In this regard, the Langmuir—Blodgett tech- nique, which enables self-organization of amphiphi- lic compounds at the interface necessary for achieving a desired molecular architecture, seems the most promis- ing. However, amphiphilic photochromic compounds are still insufciently studied both in solutions and in ultrathin films primarily due to the difculty of their synthesis, but also due to the possible undesirable altera- tions of their photophysical characteristics occurring in concequence of the introduction of a long hydro- carbon chain. In this work, an amphiphilic photochrome 1´-hexadecyl-3´,3´-dimethyl-6-nitro-1´,3´-dihydro- spiro[chromene-2,2´-indole] (SP) was obtained using a known procedure, 11 and its photophysical properties in a bulk system (solution) and at the air—water interface were investigated. Experimental Electronic absorption spectra of solutions were recorded in the wavelength range of 190—900 nm using a UV 2450 PC spectrophotometer (Shimadzu, Japan). The measurement error was ±0.3 nm. For kinetic studies, the electronic absorption spectra of solutions were recorded using an AvaSpec-2048 fiber optic spectrophotometer. A compact combined deuterium- halogen light source provided a continuous emission spectrum with high efciency and stability in the UV, visible, and near-IR ranges. The spectra were recorded in the range of 200–900 nm with a resolution of 0.1 nm and a maximum recording frequency of 100 spectra per second. Photochromic properties were studied in acetonitrile solu- tions (high purity grade) with a concentration of optically active compounds equal to 1•10 –4 mol L –1 in standard quartz cells (optical pathlength 1 cm). Irradiation with ultraviolet light at a wavelength of 365 nm was carried out using a UV lamp (Wilber- Lourmat, France, a power of 600 W cm –2 at a distance of 15 cm) * Based on the materials of the VII International Conference on Physical Chemistry of Crown Compounds, Porphyrins, and Phthalocyanines (September 9—14, 2018, Tuapse, Russia).