Long-range photoinduced charge separation in tröger bases D/A dyads

DUSSO, DIEGO; LANZA, PRISCILA A.; MONTEJANO, HERNÁN A.; RAMÍREZ, CRISTINA L.; PARISE, ALEJANDRO R.; VERA, D.MARIANO A.; LAURA MOYANO, E.; CHESTA, CARLOS A.

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2020 vol. 389

1010-6030

Troger´s base (and its derivatives) are compounds comprised of two aromatic (or polyaromatic) rings bridged by a diazocine aliphatic cycle. We report herein the photophysical properties of two series of novel Troger´s bases (TB) asymmetrically substituted by electron donor (D) and electron acceptor (A) substituents. In TB series 3, a carbonitrile group (A=CN) lies at the position 2 of the heterocycle, while position 8 is occupied by a series of D with increasing reductant capacity: H (3a), CH3 (3b), OCH3 (3c) or N(CH3)2 (3d). A novel TB series (5a-5d) which comprise the same D, but a 2,2- dicyanovinyl group (A=CHC(CN)2) as electron acceptor, was synthesized and fully characterized. TB absorption and emission energies, fluorescence quantum yields and emission lifetimes were determined in a series of aprotic solvents covering a wide range of medium polarity largely depend on the polarity of the medium and the nature of D/A pair. From the solvatochromic study on max, it is concluded that upon excitation TB´s develop large degrees of charge separation (CT). Photophysically, 3a-3c resembles 4-(N,Ndimethylamino)benzonitrile derivatives showing internal CT state dipole moments 15-17 D. For 3d and the entire series 5, CT occurs throughout the diazocine ring giving rise to giant. This is indeed an unusual result, because it strongly suggests that the aliphatic diazocine ring can couple the D/A redox centers as a  bridge would do.