Electronic Spectroscopy of Nonalternant Hydrocarbons Inside Helium Nanodroplets

Abstract

We have recorded the electronic spectra of three polycyclic aromatic hydrocarbons (acenaphtylene, fluoranthene, and benzo(k)fluoranthene) containing a five-member ring and their van der Waals complexes with argon and oxygen with a molecular beam superfluid helium nanodroplet spectrometer. Although the molecules, which differ by addition of one or two fused benzene rings to acenaphtylene, have the same point group symmetry, the spectral lineshapes show distinct differences in the number of zero phonon lines and shapes of the phonon wings. Whereas the smallest molecule (acenaphtylene) has the most complicated line shape, the largest molecule (benzo(k)fluoranthene) shows different lineshapes for different vibronic transitions. The van der Waals complexes of fluoranthene exhibit more peaks than the theoretically allowed number of isomeric complexes with argon/oxygen. The current models of molecular solvation in liquid helium do not adequately explain these discrepancies.

Synthesis, Characterization, and Electropolymerization of Extended Fused-Ring Thieno[3,4-b]pyrazine-Based Terthienyls

“…Thus, these higher energy absorptions correspond to strongly allowed transitions. The energies of these transitions agree well with the absorption energies reported for α-terthiophene [63], but also agree with localized π → π* transitions of acenapthylene [65], phenanthrene [66], and 1,10-phenanthroline [67]. As such, it is quite likely that these are not simple singular transitions for T3 – T5 , but the overlap of multiple localized π → π* transitions.…”

Absorption spectroscopy of adenine, 9-methyladenine, and 2-aminopurine in helium nanodroplets

“…Although splitting of ZPL's has been observed in many molecular systems, a complete understanding of the phenomena is still lacking. 52,[65][66][67] Analysis of the rotational band contour of the A 2 resonance of gas phase adenine is consistent with a transition involving a 1 pp* state, 14 thus corroborating its previous assignment to the 0-0 transition to the 1 L b (pp*) state. 12 In helium droplets, this transition has the largest linewidth, 12.2 cm À1 , of the observed transitions.…”

Electronic spectroscopy of benzo[g,h,i]perylene and coronene inside helium nanodroplets

“…the center of benzene rings) is 3.85 A ˚for biphenylene as compared to 2.5 A ˚for tetracene, whereas the equilibrium distance of the helium dimer is 2.96 A ˚. 51 In previous works involving large aromatic molecules, 19,20 we employed potential energy surfaces generated by summation of pairwise interactions based on benzene molecule due to the lack of ab initio potentials. Also demonstrated by the Monte Carlo simulations mentioned above, the interaction of a single helium atom with a large polycyclic molecule is regarded as descriptive of the environment of a molecule inside helium droplets.…”

“…The electronic spectroscopy of polycyclic aromatic molecules (i.e. benzene, 1,2 naphthalene, 3 anthracene, 4 tetracene, [5][6][7][8][9][10] pentacene, 5,9,10 PTCDA, 11,12 porphyrin, 9 phthalocyanines, 9,[13][14][15][16] perylene, 10,17 benzo[b]fluorine, 18 biphenylene, 19 acenaphtylene, 20 fluoranthene, 20 benzo(k)fluoranthene 20 and the S 2 ' S 0 transition of pyrene 21 ) inside helium nanodroplets has demonstrated the different solvation characteristics of these molecules. Each vibronic transition of these molecules consists of one or more sharp transitions (max.…”