The transient absorption of 1,3,5-tri-tert-butyl-pentalene

Year: 2001

Authors: Bussotti L., Foggi P., Gellini C., Moroni L., Salvi P.R.

Autors Affiliation: Laboratorio di Spettroscopia Molec., Dipartimento di Chimica, Università di Firenze, Via Gino Capponi 9, 50121 Firenze, Italy

Abstract: The transient absorption of 1,3,5-tri-tert-butyl-pentalene in cyclohexane solution has been measured at room temperature exciting at 340 nm with femtosecond pulses. Two relaxation processes have been determined, the first, very rapid, with time constant 650 fs and the second, occurring on a picosecond timescale, with estimated decay time 13 ps. The former is due to the vibronic relaxation from upper S3 levels to the S3 minimum, the latter to the decay from S3 to S0. This interpretation is in good agreement with results of ab initio calculations on pentalene and its alkyl derivatives, 1,3,5-tri-ethyl, 1,3,5-tri-sec-propyl and 1,3,5-tri-tert-butyl. MCSCF/CAS calculations, perturbatively corrected within the scheme of quasi-degenerate perturbation theory (QDPT), of vertical S0 ? Sn excitation energies allow us to study the dependence of excitation energies on substitution. Calculated S3 ? Sn and S4 ? Sn absorption spectra of pentalene at the S0, S3 and S4 equilibrium geometries that vibronic levels of S3 rather than of S4 are excited by the strong pump pulse with subsequent decay within this state.

Journal/Review: PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Volume: 3 (15)      Pages from: 3027  to: 3033

KeyWords: 1,3,5 tri tert butylpentalene; alkene derivative; cyclohexane; unclassified drug, absorption spectroscopy; article; calculation; chemical structure; energy; excitation; geometry; mathematical model; measurement; pump; temperature; theory; time
DOI: 10.1039/b103114g

Citations: 8
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