Remarkable Solvent-Dependent Excited-State Chirality:  A Molecular Modulator of Circularly Polarized Luminescence

• Published in: Journal of the American Chemical Society 2003-12, Vol.125 (50), p.15659-15665
• Main Authors: van Delden, Richard A, Huck, Nina P. M, Piet, Jacob J, Warman, John M, Meskers, Stefan C. J, Dekkers, Harry P. J. M, Feringa, Ben L
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Exact sciences and technology; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Molecular properties and interactions with photons; Physics; Radiationless transitions, quenching
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja036874d

The photochemical control of ground- and excited-state chirality of (M)-cis-(1) and (P)-trans-(2)-2-nitro-7-(dimethylamino)-9-(2‘,3‘-dihydro-1‘H-naphtho[2,1-b]-thiopyran-1‘-ylidene)-9H-thioxanthene is described. It is shown that while ground state chirality can be controlled photochemically by irradiation with light of different wavelengths, the excited state chirality can be tuned either photochemically in a similar way or by appropriate choice of solvent. In benzene solution, circularly polarized luminescence of the two isomers with opposite ground-state helicity, (M)-cis- 1 and (P)-trans-2, revealed corresponding excited states of opposite helicity. On the contrary, in n-hexane solution, circularly polarized luminescence was identical for the two forms indicating identical excited state chirality. Circularly polarized luminescence (CPL), steady-state and time-dependent fluorescence, and time-resolved microwave conductivity (TRMC) measurements in both n-hexane and benzene are reported, which provide an explanation for the remarkable solvent dependence of excited-state chirality.