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

Año: 2019

1010-6030

Tröger´s base (and its derivatives) are compounds comprised of two aromatic (orpolyaromatic) rings bridged by a diazocine aliphatic cycle. We report herein thephotophysical properties of two series of novel Tröger´s bases (TB) asymmetricallysubstituted 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 isoccupied 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 fullycharacterized. TB absorption (max  A) and emission energies (max  F), fluorescencequantum yields (F) and emission lifetimes (F) were determined in a series of aproticsolvents covering a wide range of medium polarity (2-38).max  F, FandFlargelydepend on the polarity of the medium and the nature of D/A pair. From thesolvatochromic study onmax  F, it is concluded that upon excitation TB´s develop largedegrees of charge separation (CT). Photophysically, 3a-3c resembles 4-(N,Ndimethylamino)benzonitrile derivatives showing internal CT state dipole moments (*1)of  15-17 D. For 3d and the entire series 5, CT occurs throughout the diazocine ringgiving rise to giant*1(> 25 D). This is indeed an unusual result, because it stronglysuggests that the aliphatic diazocine ring can couple the D/A redox centers as a  bridgewould do