Jaroslav Kolc

Direct observation of a doubly excited state of pleiadene

Abstract Evidence is presented that the second excited state of pleiadene (I) is of doubly excited nature. Such states are of interest in discussions of excited state and ground state reactivities and for further development of calculational methods.

Excited states of dicyclohepta[cd,gh]pentalene: Linear dichroism in a stretched polymer, magnetic circular dichroism, and calculations

Abstract Ordinary and linear dichroic uv-visible absorption spectra of dicyclohepta[ cd,gh ]pentalene have been determined from measurements on solutions in 3-methylpentane and in stretched sheets of ethylene-vinyl acetate copolymer at 77 K. Magnetic circular dichroic spectrum was measured at room temperature. The spectra reveal the presence of numerous separate electronic transitions and permit assignment of state symmetries and of relative direction and sense of some magnetic dipole transition moments between excited states with respect to direction and sense of electric dipole transition moments from ground to these excited states. π-electron calculations account well for the results, including the absolute signs of the peaks in the MCD spectrum (with a single exception).

Excited states of dinaphth[de-1, 2, 3; d′e′-5, 6, 7]azulene: Polarized absorption in stretched polymers and magnetic circular dichroism

Abstract UV-visible polarized absorption spectra of dinaphth[de-1,2,3; d′e′-5,6,7]azulene I have been determined from measurements of linear dichroism in stretched polymer sheets. Magnetic circular dichroic (MCD) spectra have been measured in solution and help to distinguish individual electronic transitions. π-Electron calculations of transition energies, oscillator strengths, and polarization directions are in good agreement with the experimental data and permit a straightforward correlation of the low-energy part of the spectrum of I with that of the parent pleiadiene II.

Photochromism: nature of the coloured form of 1,2-dihydroquinolines

1-Cyano-1,2-dihydro-2-hydroxyquinolines when subjected to low-temperature rigid-matrix photochemistry and then warmed give rise principally to N-cyano-o-aminocinnamaldehyde. This result verifies the fact that the core molecular structure of the photocoloured forms of the 1,2-dihydroquinolines previously suggested is correct.

Higher Excited States and Vibrationally Hot Excited States: How Important are they in Organic Photochemistry in Dense Media?

In photochemical reactions of organic molecules in fluid or rigid solutions, and even in the gas phase at moderate to high pressures, it is usually assumed without question that internal conversion to the lowest excited electronic state and thermal equilibration of vibrational motion occur much more rapidly than any chemical transformations, so that direct irradiation first produces cool S1, or possibly directly cool T1 if special structural features greatly enhance the rate of intersystem crossing relative to thermalization (e.g., heavy atoms), and sensitization produces cool T1, before any chemical reactions occur. The reacting species is therefore assumed to be thermalized S1 or T1, except perhaps if S2 (or T2 is so close in energy as to be thermally accessible, and kinetic schemes are set up accordingly. These assumptions represent an analogy to Kasha’s rule which states that thermalized S1 and T1 states are the only ones from which significant light emission is observed in dense media.