Polarized fluorescence spectrum of triphenylene in a n-heptane single crystal. Evidence for deformed molecules

Abstract

The polarized fluorescence spectrum of triphenylene as a guest in a n-heptane single crystal has been studied at 4 K. The transitions in the fluorescence spectrum are analyzed in terms of known ir and Raman active vibrations in the ground state. A small matrix induced deformation of triphenylene, leading to an in-plane change of geometry is proposed. Polarization data are analyzed in terms of this model.

Zero kinetic energy photoelectron spectroscopy of triphenylene

“…[31][32][33][34][35][36][37] The first electronically excited state of triphenylene has been studied by several groups using a variety of techniques including gas phase laser induced fluorescence (LIF) 47 and matrix isolation spectroscopy. [38][39][40][41] The LIF study by Kokkin et al is in close agreement with our work in terms of frequency, intensity, and assignment, as shown in Table I. 47 The frequencies from matrix isolation spectroscopy at 1.6 K 39 are also included in Table I for comparison.…”

“…[31][32][33][34][35][36][37] So far we have reported four pericondensed species including pyrene, benzo[a]pyrene (BaP), benzo[e]pyrene (BeP), and benzo[g,h,i]perylene (BghiP) as well as three cata-condensed species including tetracene, pentacene, and chrysene. [31][32][33][34][35][36][37] Our results together with previous matrix isolation spectroscopy (MIS) [38][39][40][41] and other experimental efforts offer the possibility of a comprehensive analysis of the vibrational modes of a few selected cationic species, thereby benchmarking theoretical calculations and astrophysical modeling.…”

“…Furthermore, all MIS studies have shown a small but observable origin band, implying that the symmetry of the electronic state has perhaps been distorted. [38][39][40] Based on polarization analysis, Lamotte et al have indeed confirmed the symmetry of the S 1 state to be C 2v in their matrix. 40…”

“…The scaling factor is indicative of deformation of the molecular frame relative to that of free space gas phase molecules. 39,40 This effect is not too surprising given the seemingly floppy shape of the molecular frame. Furthermore, all MIS studies have shown a small but observable origin band, implying that the symmetry of the electronic state has perhaps been distorted.…”

“…The observed vibronic bands do indeed correspond to those from the S 1 ← S 0 transition. [38][39][40]47 The assignment in Table I is based on several considerations. First, even with HT coupling, selection rules for electric dipole transitions are still obeyed, hence only vibronic transitions with an overall symmetry species of e are allowed.…”