title: Modeling the high-energy electronic state manifold of adenine: Calibration for nonlinear electronic spectroscopy.
abstract: Pump-probe electronic spectroscopy using femtosecond laser pulses has evolved into a standard tool for tracking ultrafast excited state dynamics. Its two-dimensional (2D) counterpart is becoming an increasingly available and promising technique for resolving many of the limitations of pump-probe caused by spectral congestion. The ability to simulate pump-probe and 2D spectra from ab initio computations would allow one to link mechanistic observables like molecular motions and the making/breaking of chemical bonds to experimental observables like excited state lifetimes and quantum yields. From a theoretical standpoint, the characterization of the electronic transitions in the visible (Vis)/ultraviolet (UV), which are excited via the interaction of a molecular system with the incoming pump/probe pulses, translates into the determination of a computationally challenging number of excited states (going over 100) even for small/medium sized systems. A protocol is therefore required to evaluate the fluctuations of spectral properties like transition energies and dipole moments as a function of the computational parameters and to estimate the effect of these fluctuations on the transient spectral appearance. In the present contribution such a protocol is presented within the framework of complete and restricted active space self-consistent field theory and its second-order perturbation theory extensions. The electronic excited states of adenine have been carefully characterized through a previously presented computational recipe [Nenov et al., Comput. Theor. Chem. 1040-1041, 295-303 (2014)]. A wise reduction of the level of theory has then been performed in order to obtain a computationally less demanding approach that is still able to reproduce the characteristic features of the reference data. Foreseeing the potentiality of 2D electronic spectroscopy to track polynucleotide ground and excited state dynamics, and in particular its expected ability to provide conformational dependent fingerprints in dimeric systems, the performances of the selected reduced level of calculations have been tested in the construction of 2D electronic spectra for the in vacuo adenine monomer and the unstacked adenine homodimer, thereby exciting the Lb/La transitions with the pump pulse pair and probing in the Vis to near ultraviolet spectral window.
authors.affiliation: Dipartimento di Chimica "G. Ciamician," Università di Bologna, Via Selmi 2, IT-40126 Bologna, Italy.
authors.forename: Artur
authors.initials: A
authors.lastname: Nenov
authors.affiliation: Dipartimento di Chimica "G. Ciamician," Università di Bologna, Via Selmi 2, IT-40126 Bologna, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Giussani
authors.affiliation: Dipartimento di Chimica "G. Ciamician," Università di Bologna, Via Selmi 2, IT-40126 Bologna, Italy.
authors.forename: Javier
authors.initials: J
authors.lastname: Segarra-Martí
authors.affiliation: Dipartimento di Chimica "G. Ciamician," Università di Bologna, Via Selmi 2, IT-40126 Bologna, Italy.
authors.forename: Vishal K
authors.initials: VK
authors.lastname: Jaiswal
authors.affiliation: Université de Lyon, CNRS, Institut de Chimie de Lyon, École Normale Supérieure de Lyon, 46 Allée d'Italie, F-69364 Lyon Cedex 07, France.
authors.forename: Ivan
authors.initials: I
authors.lastname: Rivalta
authors.affiliation: Dipartimento di Fisica, Politecnico di Milano, IFN-CNR, Piazza Leonardo Da Vinci 32, IT-20133 Milano, Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Cerullo
authors.affiliation: Department of Chemistry, University of California, Irvine, California 92697-2025, USA.
authors.forename: Shaul
authors.initials: S
authors.lastname: Mukamel
authors.affiliation: Dipartimento di Chimica "G. Ciamician," Università di Bologna, Via Selmi 2, IT-40126 Bologna, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Garavelli