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Francesca Terenziani

Publications and source records attributed to Francesca Terenziani.

9 recordsLinked to original sources
arXiv2025

Luminescent Trityl-based Diradicaloids: A Theoretical and Experimental Assessment of Charge-Resonance in Low-Lying Excited States

The tris(2,4,6-trichlorophenyl)methyl radical (TTM) has inspired the synthesis of several luminescent diradicals and diradicaloids, providing an extraordinary opportunity to control the nature of the low-lying excited states by fine-tuning the diradical character. However, the photophysical properties of TTM-derived diradicals remain not fully understood yet. Here we present a combined theoretical and experimental investigation on TTM-derived diradicals to elucidate the origin of their luminescence. The theoretical analysis focuses on a series of symmetric TTM-derived diradicals with singlet ground state, featuring radical moieties linked by pi-conjugated spacers of different length. The nature of the lowest excited electronic states that control their photophysical behaviour is discussed in detail. The study is complemented by a complete spectroscopic characterization of the TTM-TTM diradical, synthesized using a novel, simpler and more efficient procedure exploiting the unique reactivity of TTM. The lowest excited states of the diradicals differ qualitatively from those of TTM: two novel low-lying states emerge in the diradical, due to charge resonance (CR) between the two radical units. The lowest CR state is a dark state for symmetric diradicals. The CR nature explains the blue-shifted emission observed by increasing the distance between the radical centres as seen in TTM-ph-TTM. This insight suggests different design strategies to improve the luminescence properties of TTM-derived diradicals

physics.chem-ph↗
arXiv2020

Optical spectra in condensed phases: how the medium polarizability affects charge-transfer dyes

When designing molecular functional materials, the properties of the active specie, the dye, must be optimized fully accounting for environmental effects. Here we present an effective model to account for the spectroscopic effects of the medium electronic polarizability on the properties of charge-transfer dyes. Different classes of molecules are considered and the proposed antiadiabatic approach to solvation is contrasted with the adiabatic approach, currently adopted in all quantum chemical approaches to solvation. Transition frequencies and band-shapes are addressed, and the role of the medium polarizability on symmetry-breaking phenomena is also discussed.

physics.chem-ph↗
arXiv2020

Antiadiabatic View of Fast Environmental Effects on Optical Spectra

An antiadiabatic approach is proposed to model how the refractive index of the surrounding medium affects optical spectra of molecular systems in condensed phases. The approach solves some of the issues affecting current implementations of continuum solvation models and more generally of effective models where a classical description is adopted for the molecular environment.

cond-mat.mtrl-sci↗
arXiv2003

Supramolecular interactions in clusters of polar and polarizable molecules

We present a model for molecular materials made up of polar and polarizable molecular units. A simple two state model is adopted for each molecular site and only classical intermolecular interactions are accounted for, neglecting any intermolecular overlap. The complex and interesting physics driven by interactions among polar and polarizable molecules becomes fairly transparent in the adopted model. Collective effects are recognized in the large variation of the molecular polarity with supramolecular interactions, and cooperative behavior shows up with the appearance, in attractive lattices, of discontinuous charge crossovers. The mean-field approximation proves fairly accurate in the description of the gs properties of MM, including static linear and non-linear optical susceptibilities, apart from the region in the close proximity of the discontinuous charge crossover. Sizeable deviations from the excitonic description are recognized both in the excitation spectrum and in linear and non-linear optical responses. New and interesting phenomena are recognized near the discontinuous charge crossover for non-centrosymmetric clusters, where the primary photoexcitation event corresponds to a multielectron transfer.

cond-mat.mtrl-sci↗
arXiv2003

Static polarizability of molecular materials: environmental and vibrational contributions

Modeling the dielectric behavior of molecular materials made up of large pi-conjugated molecules is an interesting and complex task. Here we address linear polarizabilities, and the related dielectric constant, of molecular crystals and aggregates made up of closed-shell pi-conjugated molecules with either a non-polar or largely polar ground-state, and also examine the behavior of mixed-valence (or charge-transfer) organic salts. We recognize important collective phenomena due to supramolecular interactions in materials with large molecular polarizabilities, and underline large vibrational contributions to the polarizability in materials with largely delocalized electrons.

physics.chem-ph↗
arXiv2003

Time-resolved spectra of polar-polarizable chromophores in solution

A recently proposed model for steady-state spectra of polar-polarizable chromophores is extended to describe time-resolved spectra. The model, based on a two-state picture for the solute and on a continuum overdamped description for the (polar) solvent, grasps the essential physics of solvation dynamics, as demonstrated by the comparison with experimental spectra. The solute (hyper)polarizability is responsible for spectroscopic features that cannot be rationalized within the standard picture based on a linear perturbative treatment of the solute-solvent interaction. In particular, the temporal evolution of band-shapes and the appearance of temporary isosbestic points, two common puzzling features of observed spectra, are natural consequences of the molecular hyperpolarizability and of the consequent coupling between solvation and vibrational degrees of freedom.

physics.chem-ph↗
arXiv2001

Vibronic contributions to resonant NLO responses: two-photon absorption in push-pull chromophores

Two-photon absorption (TPA) spectra of push-pull chromophores are described in terms of a two-state model accounting for electron-vibration coupling. Vibrations have two main effects in TPA spectra. The most obvious one is the appearance of a vibrational structure in the spectrum; in this respect we find large Herzberg-Teller contributions. The second effect was not recognized so far: vibrational states contribute a new channel to TPA process, that shows up with a blue-shift and a distortion of the spectrum. Vibrational-channel contributions to other NLO responses are shortly discussed.

physics.chem-ph↗
arXiv2001

Static NLO susceptibilities: testing approximation schemes against exact results

The reliability of the approximations commonly adopted in the calculation of static optical (hyper)polarizabilities is tested against exact results obtained for an interesting toy-model. The model accounts for the principal features of typical nonlinear organic materials with mobile electrons strongly coupled to molecular vibrations. The approximations introduced in sum over states and finite field schemes are analyzed in detail. Both the Born-Oppenheimer and the clamped nucleus approximations turn out to be safe for molecules, whereas for donor-acceptor charge transfer complexes deviations from adiabaticity are expected. In the regime of low vibrational frequency, static susceptibilities are strongly dominated by the successive derivatives of the potential energy and large vibrational contributions to hyperpolarizabilities are found. In this regime anharmonic corrections to hyperpolarizabilities are very large, and the harmonic approximation, exact for the linear polarizability, turns out totally inadequate for nonlinear responses. With increasing phonon frequency the role of vibrations smoothly decreases, until, in the antiadiabatic (infinite vibrational frequency) regime, vibrations do not contribute anymore to static susceptibilities, and the purely electronic responses are regained.

physics.chem-ph↗