Dynamics of the Excited States of p-Terphenyl and Tetracene: Solute–Solvent Interaction

Abstract

The time-resolved fluorescence of p-terphenyl, 2,2″-dimethyl-p-terphenyl (dm-terphenyl), and tetracene dissolved in solvents was measured with fluorescence up-conversion and time-correlated single-photon counting. We characterized the relaxation dynamics of vibrational energy in these three molecules by examining their properties in solvents of varied physical properties. According to the measured curves of fluorescence decays obtained at excitation wavelength 266/256 nm, we propose that p-terphenyl and dm-terphenyl both undergo initially an ultrafast intramolecular redistribution of vibrational energy. A conformational relaxation of p-terphenyl in excited-state S 1 with time constant 6–13 ps is proposed from its linear dependence on the viscosity of solvents. This process and vibrational energy relaxation are accelerated in a protic solvent involving efficient coupling to the high-energy bath modes of the solvent. Because the torsional conformational change of dm-terphenyl is effectively inhibited by the steric hindrance imposed by its methyl substituents, its vibrational relaxation is found to be independent of the viscosity of the solvent but remains rapid with time constant 5.2–8.8 ps. The time constant of vibrational relaxation in tetracene is observed to be 12–16 ps, with no evident dependence on solvent viscosity or thermal diffusivity. The fact that accepting modes with greater energy are more effective in transferring energy for a system with a large excess of vibrational energy is proposed to explain the ratio of the rates of vibrational relaxation for methanol MeOH/MeOD ≈ 2.

Optical properties of para‐oligophenylenes: A case study of electronic absorption spectrum and relaxation dynamics of terphenyl

“…We turn our attention to analyze the solvent and temperature effects on the absorption spectral features. In connection to that, we show the experimental spectra reported by Volkmer et al [1], Liu et al [7] and Braem et al [6] (cf., Figure S4 in Supporting Information). Both Figure 4 (upper panel) and Figure S4 depict nearly solvent-independent and temperature-independent absorption spectral behavior.…”

Vacuum UV Polarization Spectroscopy ofp-Terphenyl

“…The fluorescence emission is thus characterized by a well-resolved vibrational fine structure, in marked contrast to the broad and featureless absorption. 3,10,11,14,16,18,25 Band A overlaps short axis-polarized absorbance B with a maximum close to 35700 cm −1 (280 nm). Several short axispolarized transitions are predicted in this region, e.g., 1 1 B 2 , 2 B 2 and 1 1 B 3 states of the D 2 rotamer, and 1 1 B u and 2 1 B u states of the C 2h rotamer, but they are all predicted to be very weak (Tables 1 and 2).…”

Photoluminescence properties of polystyrene-hosted fluorophore thin films

“…The fine emission peaks in PTP, on the other hand, are known to arise from its low-energy twisting vibrational modes of the terminal phenyl rings about the long axis. 12,17,24 The Stoke's shift of the first peak is due to the twisting vibration while the second peak is due to central bond stretching vibration of the pi-electrons. Calculations show 24 that the bond stretching vibration has a larger pi-bond order which can be related to the larger difference in transitional dipole moment, and hence, to a larger Stoke's shift of the second peak.…”

“…Due to short axis symmetry of their molecular geometry, these fluors have much lower dipole moments than Coumarin 6, thus making them less affected by the solvatochromism of the medium. 17 Therefore, the fluor selection covers a large spectrum of fluor-types, from auxochromic (Coumarin 6) to phenyl-chain (PTP) and oxazole (POPOP and PPO) substitutions, in a plausible, unified thin-film fabrication recipe. These fluors have not been studied under such unified conditions: identical thin-film recipes with shared thickness and concentration pairings that may allow their relative spectral characterization within a given sensor development step, thus motivating the research.…”