Sudden polarization in the twisted, phantom state of tetraphenylethylene detected by time-resolved microwave conductivity

• Published in: Journal of the American Chemical Society 1993-04, Vol.115 (8), p.3286-3290
• Main Authors: Schuddeboom, Wouter, Jonker, Stephan A, Warman, John M, de Haas, Matthijs P, Vermeulen, Martien J. W, Jager, Wolter F, de Lange, Ben, Feringa, Ben L, Fessenden, Richard W
• Format: Article
• Language: English
• Subjects: 360606 - Other Materials- Physical Properties- (1992-); 400102 - Chemical & Spectral Procedures; 400201 - Chemical & Physicochemical Properties; 400500 - Photochemistry; ALKENES; AROMATICS; CHEMICAL REACTIONS; Chemistry; DIELECTRIC PROPERTIES; DIPOLE MOMENTS; DISPERSIONS; ELECTRICAL PROPERTIES; ELECTROMAGNETIC RADIATION; ETHERS; Exact sciences and technology; FLUORESCENCE; General and physical chemistry; HYDROCARBONS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ISOMERIZATION; LUMINESCENCE; MAGNETIC RESONANCE; MATERIALS SCIENCE; MICROWAVE RADIATION; MIXTURES; NUCLEAR MAGNETIC RESONANCE; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PHOTOCHEMICAL REACTIONS; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); PHYSICAL PROPERTIES; RADIATIONS; RESONANCE; SOLUTIONS
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00061a029

Photoexcitation of the symmetrical molecules tetraphenylethylene and tetra-p-methoxyphenylethylene dissolved in saturated hydrocarbon solvents results in a transient increase in the dielectric loss of the solutions as monitored using the nanosecond time-resolved microwave conductivity (TRMC) technique. This provides direct evidence for the dipolar, or [open quotes]zwitterionic,[close quotes] nature of the [sup 1]p* phantom state formed from S[sub 1] by rotation around the central carbon-carbon bond. Dipole relaxation occurs mainly by charge inversion between the two energetically equivalent zwitterionic configurations. Z[sub [+-]], on a timescale of several picoseconds. A minimum dipole moment of ca. 7.5 D for the individual Z[sub [+-]] states is found. The fluorescence of TPE in alkane solvents has two decay components, one with a decay time less than 200 ps and a second with a decay time of 1.9 ns. The former ([lambda][sub max] [approx] 490 nm) is assigned to emission from the partially relaxed S[sub 1] state prior to twisting. The latter ([lambda][sub max] [approx] 540 nm) is assigned to emission from a small, ca. 1%, concentration of the relaxed S[sub 1] state in equilibrium with the [sup 1]p* state in saturated hydrocarbon solvents. 27 refs., 2 figs., 2 tabs.