Triarylamine-perchlorotriphenylmethyl radicals (TARA-PCTM) may be viewed as open-shell mixed valence donor-acceptor compounds that exhibit strong charge-transfer (CT) bands in the visible to NIR spectral region. While open-shell molecules generally do not fluoresce at RT, we observed a surprisingly strong fluorescence from the highly polar excited CT state of the TARA-PCTM radicals in the visible and NIR spectral region. The fluorescence quantum yield is enhanced by a factor of up to 150 compared to the unsubstituted perchlorotriphenylmethyl radical. The enhancement depends on the donor strength of the TARA moiety which was tuned by small substituents (OMe, Me, Cl, CN, and NO 2 ) attached to the phenyl groups, thus forming a series of donor-acceptor species that mainly differ by the free energy difference of the excited CT state and the ground state. The reorganization parameters of the CT process were extracted by Bixon-Jortner fits to either the absorption or the fluorescence bands. The dynamics of the nonradiative back-electron transfer were investigated by time-resolved fluorescence and transient absorption spectroscopy in the ps to ns time regime. We observed a strong deviation of the back-electron transfer rate from the expected inverted Marcus behavior which might be due to anharmonic effects.

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We report an investigation of four differently substituted boroles by resonance Raman (RR) spectroscopy with the aim of gaining insight into the structural changes that occur upon electronic π -π * excitation in the five-membered BC 4 ring. Such boroles are prototypes for the theory of antiaromaticity, because the empty p z orbital at the boron interacts with the π system of the carbon backbone to delocalize the four π electrons. The magnitude of this interaction depends on the substituents at the boron atom. In all compounds, an intense band appears around 1600 cm −1 , which can be assigned to a C C stretching vibration. The selective amplification of this mode indicates an expansion of the borole ring upon electronic excitation. The resonant enhancement of another mode at around 1300 cm −1 , which can be assigned to a vibration between the boron and the substituent, gives evidence that the degree of antiaromaticity in the borole depends strongly on the interaction between the substituent at the boron atom with the empty p z orbital of the boron. When the boron is connected to a ferrocene, this band appears with high intensity, indicating a strong interaction between B and Fe. Furthermore, we studied the dependence of the excitation wavelength on the Raman intensities. In addition, we used DFT calculations to determine the vibrational wavenumbers.

The photophysics of the B (1)B(1) state of isolated cyclopropenylidene, c-C(3)H(2), has been studied by femtosecond time-resolved photoionisation and photoelectron spectroscopy. The carbene was produced by flash pyrolysis of 3-chlorocycloprop-1-ene. The bands at 266.9 nm and 264.6 nm have been investigated. The excited state deactivates in a two step process. The first time constant of less than 50 fs corresponds most likely to a nonradiative transition to the A-state, the second one on the order of 200 fs describes the internal conversion to the electronic ground state. The data are compared to those measured for the chlorinated carbene c-C(3)HCl. In the photoelectron spectrum of c-C(3)H(2) resonances were observed which can be assigned to members of a Rydberg d-series.