Vibrational Energy Transfer in Highly Excited Bridged Azulene-Aryl Compounds:  Direct Observation of Energy Flow through Aliphatic Chains and into the Solvent

Abstract

Intra- and intermolecular vibrational energy flow in vibrationally highly excited bridged azulene-(CH2) n -aryl (n = 0,1,3; aryl = benzene or anthracene) compounds is observed using time-resolved pump−probe laser spectroscopy. Light absorption in the azulene S1-band, followed by fast internal conversion, leads to vibrational excitation at the azulene side of the molecules. Subsequent energy flow through the aliphatic chain to the aryl group at the other side of the molecules and vibrational energy transfer into a surrounding liquid solvent bath are measured either by probing the red edge of the azulene S3-absorption band at 300 nm and/or the anthracene S1-absorption band at 400 nm. The data are analyzed by representing the intramolecular energy flux as a diffusion process and using hot absorption spectra of the two chromophores of the compounds for measuring their energy contents. A fit to all of the experimental signals leads to an energy conductivity of a single C−C bond of κ CC = (10 ± 1) cm-1 K-1 ps-1 (with energies measured in cm-1). Depending on the substituent and the length of the chain, this models yield intramolecular energy transfer times of 1.2−4 ps. Energy transfer to the solvent 1,1,2-trichloro-trifluoro-ethane, on the other hand, is characterized by an exponential loss profile with a cooling time constant of (21 ± 2) ps, independent of the substituent and the same as for bare azulene.

Solvent-assisted intramolecular vibrational energy redistribution of S1 perylene in ketone solvents

“…This time constant is much longer than the τ 3 value observed in the present study, 1.8 -4.9 ps, even taking the difference in the electronic states, S 0 and S 1 , into account. It is also noted that Schwarzer et al reported the intramolecular energy transfer rate of 1.2 -4 ps and the VET rate of 21 ps for electronically excited linked azulene-aryl compounds [25].…”

Constant-speed vibrational signaling along polyethyleneglycol chain up to 60-Å distance

“…800-K transient temperature gradient was found by Dlott and coworkers in self-assembled monolayers of alkanes at a gold surface (26,27). A ballistic contribution to energy transport was reported for single-wall carbon nanotubes (28) and for several other systems (29)(30)(31).In this paper we use RA 2DIR spectroscopy to investigate the energy transport and dissipation in a series of PEG oligomers featuring an azido moiety and succinimide ester at two ends of the oligomer. The cross-peaks among N ≡ N and several other stretching modes, including three C ¼ O, and C-N-C modes were measured and analyzed.…”

Vibrational relaxation of CH3I in the gas phase and in solution

“…8,24 Pump-probe experiments directly observe energy flow within and out of a molecule by exciting a nonstationary vibrational state with one laser pulse and then probing the evolution of the system as a function of time with a second pulse. 25,26 Infrared absorption, [27][28][29][30][31][32] anti-Stokes Raman scattering, [33][34][35][36][37] and ultraviolet absorption [38][39][40][41][42][43][44][45][46][47][48][49] are the most common methods for probing the vibrational dynamics in the ground electronic state and are generally most useful in the condensed phase where it is possible to obtain a high density of vibrationally excited molecules. In fact, there are relatively few timeresolved studies of IVR in the ground electronic state for gas phase systems.…”