New cationic spiropyrans with photoswitchable NIR fluorescence

Anastasia S Kozlenko; Ilya V Ozhogin; Artem D Pugachev; Irina A Rostovtseva; Nadezhda I Makarova; Natalya V Demidova; Valery V Tkachev; Gennady S Borodkin; Anatoly V Metelitsa; Islam M El-Sewify; Boris S Lukyanov

doi:10.1016/j.saa.2023.122712

New cationic spiropyrans with photoswitchable NIR fluorescence

Spectrochim Acta A Mol Biomol Spectrosc. 2023 Sep 5:297:122712. doi: 10.1016/j.saa.2023.122712. Epub 2023 Apr 7.

Affiliations

¹ Institute of Physical and Organic Chemistry, Southern Federal University, 194/2 Stachka ave., 344090 Rostov-on-Don, Russian Federation. Electronic address: kozlenko@sfedu.ru.
² Institute of Physical and Organic Chemistry, Southern Federal University, 194/2 Stachka ave., 344090 Rostov-on-Don, Russian Federation.
³ North-Caucasus Federal University, 1 Pushkina str., Stavropol 355017, Russian Federation.
⁴ Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry RAS, 1Ac. Semenov ave., 142432 Chernogolovka, Moscow Region, Russian Federation.
⁵ Department of Chemistry, Faculty of Science, Ain Shams University, 11566 Cairo, Abbassia, Egypt.

PMID: 37054564
DOI: 10.1016/j.saa.2023.122712

Abstract

Visible-light-mediated photochromic compounds with NIR absorption and fluorescence are of great interest for use in different biomedical applications. In this work, new representatives of spiropyrans with conjugated cationic 3H-indolium substituents in different positions of 2H-chromene moiety were synthesized. The electron-donating methoxy groups were introduced in the uncharged indoline and charged indolium cycles to form the effective conjugation chain between the hetarene moiety and the cationic fragment for reaching NIR absorption and fluorescence. The molecular structure and the effects of cationic fragment position on the mutual stability of the spirocyclic and merocyanine forms of compounds were carefully studied in the solutions and solid state by NMR, IR, HRMS, single-crystal XRD, and quantum chemical calculations. It was found that the obtained spiropyrans demonstrate positive or negative photochromism depending on the cationic fragment's position. One of spiropyrans has shown bidirectional photochromic properties induced exclusively by visible light of different wavelengths in both directions. The photoinduced merocyanine forms of compounds possessed far-red shifted absorption maxima and NIR fluorescence, which makes them prospective fluorescent probes for bioimaging.

Keywords: Fluorescence; Merocyanine; Molecular switches; NIR; Photochromism; Spiropyrans.