TY - JOUR

T1 - Photochemical and photophysical properties of aza[6]helicenes synthesized via EDA complex initiated visible-light-mediated photocyclization

AU - Tamozhnikova, Veronica S.

AU - Mekeda, Igor S.

AU - Balakhonov, Roman Yu

AU - Ershov, Kirill S.

AU - Baklanov, Alexei V.

AU - Buravlev, Alexander A.

AU - Glebov, Evgeni M.

AU - Shirinian, Valerii Z.

N1 - Veronica S. Tamozhnikova, Igor S. Mekeda, Roman Yu. Balakhonov, Kirill S. Ershov, Alexei V. Baklanov, Alexander A. Buravlev, Evgeni M. Glebov, Valerii Z. Shirinian, Photochemical and photophysical properties of aza[6]helicenes synthesized via EDA complex initiated visible-light-mediated photocyclization, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Volume 363, Part 2, 2026, 128406, ISSN 1386-1425, https://doi.org/10.1016/j.saa.2026.128406 V.S.T., K.S.E., A.V.B. and E.M.G. (Voevodsky Institute of Chemical Kinetics and Combustion SB RAS) acknowledge the core funding from the Russian Federal Ministry of Science and Higher Education (FWGF2026-0011). Photochemical synthesis and NMR-studies were carried out with financial support from Russian Science Foundation (project No. 25-73-20098). Characterization of compounds and NMR-monitoring were performed using the equipment of the Center for molecular composition studies of INEOS RAS.

PY - 2026/12/15

Y1 - 2026/12/15

N2 - We have synthesized three new six-membered fluorescent azahelicenes of naphthofuroquinoline (NFQ) series via blue LED-induced and electron donor–acceptor (EDA) complex mediated photocyclization of 1-naphthyl naphtho[2,1- b ]furans. The concise and effective photochemical approach to the synthesis of aza[6]helicenes (Hel) was made possible by the ability of the starting naphthofuran acyl oxime to form EDA complexes with tertiary amines. Performed synthetic studies and 1H NMR monitoring showed that acyl oximes of the naphthofuran series form a very effective EDA complex with diazabicyclo(5.4.0)undec-7-ene (DBU) with a bathochromic shift of the absorption band, which opens the possibility of using blue LED radiation for their photocyclization. The photophysical and photochemical properties of Hels in typical organic solvents were described. Both electronic absorption and fluorescence spectra were found to be acid-dependent. In the most interesting case of 8-(4-(trifluoromethyl)phenyl)benzo[ f ]naphtho[1′,2′:4,5]furo[2,3- c ]quinolone in CH3CN, the fluorescence quantum yield is modulated by acidification from moderate (25%) to quite high (63%). Acidochromism in the presence of trifluoroacetic acid is caused by the formation of two successive complexes, [HelH+…CF3COO−] and [HelH+…CF3COO−…CF3COOH]. The equilibrium constants are determined. Hels are photochemically stable in chlorine-free solvents. In chloroform and dichloromethane (DCM) photoprotonation was observed, occurring from both singlet and triplet excited states. The studied helicenes promoted the formation of singlet oxygen in acetonitrile solutions with a moderate (30–40%) quantum yield.

AB - We have synthesized three new six-membered fluorescent azahelicenes of naphthofuroquinoline (NFQ) series via blue LED-induced and electron donor–acceptor (EDA) complex mediated photocyclization of 1-naphthyl naphtho[2,1- b ]furans. The concise and effective photochemical approach to the synthesis of aza[6]helicenes (Hel) was made possible by the ability of the starting naphthofuran acyl oxime to form EDA complexes with tertiary amines. Performed synthetic studies and 1H NMR monitoring showed that acyl oximes of the naphthofuran series form a very effective EDA complex with diazabicyclo(5.4.0)undec-7-ene (DBU) with a bathochromic shift of the absorption band, which opens the possibility of using blue LED radiation for their photocyclization. The photophysical and photochemical properties of Hels in typical organic solvents were described. Both electronic absorption and fluorescence spectra were found to be acid-dependent. In the most interesting case of 8-(4-(trifluoromethyl)phenyl)benzo[ f ]naphtho[1′,2′:4,5]furo[2,3- c ]quinolone in CH3CN, the fluorescence quantum yield is modulated by acidification from moderate (25%) to quite high (63%). Acidochromism in the presence of trifluoroacetic acid is caused by the formation of two successive complexes, [HelH+…CF3COO−] and [HelH+…CF3COO−…CF3COOH]. The equilibrium constants are determined. Hels are photochemically stable in chlorine-free solvents. In chloroform and dichloromethane (DCM) photoprotonation was observed, occurring from both singlet and triplet excited states. The studied helicenes promoted the formation of singlet oxygen in acetonitrile solutions with a moderate (30–40%) quantum yield.

KW - Фотоциклизация

KW - Аза[6]гелицены

KW - Флуоресценция

KW - Ацидохромизм

KW - Фотопротонирование

KW - Синглетный кислород

KW - Photocyclization

KW - Aza[6]helicenes

KW - Fluorescence

KW - Acidochromism

KW - Photoprotonation

KW - Singlet oxygen

UR - https://www.mendeley.com/catalogue/808ff6b6-569d-362e-8f20-4504906e3ae7/

UR - https://www.scopus.com/pages/publications/105044544367

U2 - 10.1016/j.saa.2026.128406

DO - 10.1016/j.saa.2026.128406

M3 - Article

C2 - 42442315

VL - 363

JO - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

JF - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

SN - 1386-1425

IS - 2

ER -