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

DUSSO, DIEGO; PRISCILA CASTRONUOVO; RAMIREZ, CRISTINA; PARISE, ALEJANDRO; D. MARIANO VERA; ELIZABETH L. MOYANO; CHESTA, CARLOS

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2019

1010-6030

Photophysical properties of two series of novel Tröger bases (TB) nonsymmetrically substituted by electron donor (D) and electron acceptor (A) substituents were studied. In TB series 3, a carbonitrile group (A=CN) lies at heterocycle´s position 2, 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 (2-37). , and largely depend on the polarity of the medium and the nature of D/A pair. From the solvatochromic study on , it is concluded that upon excitation TB´s develop large degrees of charge separation (CT). Photophysically, 3a-3c resembles 4-(N,N-dimethylamino)benzonitrile derivatives showing twisted internal CT state (TICS) dipole moments ( ) of  15-17 D. For 3d and the entire series 5, CT occurs throughout the diazocine ring giving rise to giant (> 25 D).