Excimer states in microhydrated adenine clusters

• Published in: Physical chemistry chemical physics : PCCP Vol. 12; no. 33; pp. 9632 - 9636
• Main Authors: Smith, V. R, Samoylova, E, Ritze, H.-H, Radloff, W, Schultz, T
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2010
• Subjects: Adenine - chemistry; Chemistry; Exact sciences and technology; General and physical chemistry; Hydrogen Bonding; Ions - chemistry; Photoelectron Spectroscopy; Thermodynamics; Time Factors; Water - chemistry; Water; Photoelectron spectrum; Adenine; Pump; Relaxation; Dark state; Lifetime; Excimer; fs range; Ionization potential; Mass spectrum; Dimer; Monomer; ns range; Electrons; Excited state; Hydrogen bond
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c003967e

We present femtosecond pump-probe mass and photoelectron spectra for adenine (A) and microhydrated A m (H 2 O) n clusters. Three distinct relaxation processes of photoexcited electronic states were distinguished: in unhydrated A, relaxation of the optically bright ππ* state occurred via the dark nπ* state with respective lifetimes of <0.1 and 1.3 ps. In microhydrated clusters A(H 2 O) n , relaxation via the nπ* state is quenched by a faster relaxation process, probably involving πσ* states. For the predominantly hydrogen-bonded adenine dimer (A 2 ), excited state relaxation is dominated by monomer-like processes. When the adenine dimer is clustered with several water molecules, we observe a nanosecond lifetime from excimer states in π-stacked clusters. From the electron spectra we estimate adiabatic ionization potentials of 8.32 eV (A), 8.27 eV (A(H 2 O) 1 ), 8.19 eV (A(H 2 O) 2 ), 8.10 eV (A(H 2 O) 3 ), 8.18 eV (A 2 ), and 8.0 eV (A 2 (H 2 O) 3-5 ). Femtosecond pump-probe mass and electron spectroscopy identified an excimer state in stacked adenine-water clusters.