Scientific Results

Understanding the influence of disorder on the exciton dynamics and energy transfer in Zn-phthalocyanine H-aggregates

Year: 2018

Authors: Doria S., Lapini A., Di Donato M., Righini R., Azzaroli N., Iagatti A., Caram J.R., Sinclair T.S., Cupellini L., Jurinovich S., Mennucci B., Zanotti G., Paoletti A.M., Pennesi G., Foggi P.

Autors Affiliation: European Laboratory for Non Linear Spectroscopy (LENS), Università Degli Studi di Firenze, via Nello Carrara 1, Sesto Fiorentino, Florence, 50019, Italy; Dipartimento di Chimica Ugo Schiff, Università Degli Studi di Firenze, via della Lastruccia 3-13, Sesto Fiorentino, Florence, 50019, Italy; CNR-INO, Consiglio Nazionale Delle Ricerche-Istituto Nazionale di Ottica, Largo Fermi 6, Florence, 50125, Italy; Chemistry and Biochemistry Department, UCLA, 607 Charles E. Young Drive East, Los Angeles, CA 90095-1569, United States; Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via G. Moruzzi 13, Pisa, 56124, Italy; CNR-ISM, Consiglio Nazionale Delle Ricerche-Istituto Struttura della Materia, via Salaria Km. 29.5, Monterotondo Stazione, Rome, 00015, Italy; Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, via Elce di Sotto 8, Perugia, 06100, Italy; CNR-ICCOM, Consiglio Nazionale Delle Ricerche-Istituto-Istituto di Chimica Dei Composti OrganoMetallici, via Madonna del Piano 10, Sesto Fiorentino, Firenze, 50019, Italy

Abstract: The photophysics of 9(19), 16(17), 23(24)-tri-tert-butyl-2-[ethynyl-(4-carboxymethyl) phenyl] phthalocyaninatozinc(II) and its H-aggregates is studied in different solvents by means of ultrafast non-linear optical spectroscopy and computational modeling. In non-coordinating solvents, both stationary and time-resolved spectroscopies highlight the formation of extended molecular aggregates, whose dimension and spectral properties depends on the concentration. In all the explored experimental conditions, time-resolved transient absorption experiments show multi exponential decay of the signals. Additional insights into the excited state relaxation mechanisms of the system is obtained with 2D electronic spectroscopy, which is employed to compare the deactivation channels in the absence or presence of aggregates. In ethanol and diethylether, where only monomers are present, an ultrafast relaxation process among the two non-degenerate Q-states of the molecule is evidenced by the appearance of a cross peak in the 2D-maps. In chloroform or CCl4, where disordered H-aggregates are formed, an energy transfer channel among aggregates with different composition and size is observed, leading to the non-radiative decay towards the lower energy dark state of the aggregates. Efficient coupling between less and more aggregated species is highlighted in two-dimensional electronic spectra by the appearance of a cross peak. The kinetics and intensity of the latter depend on the concentration of the solution. Finally, the linear spectroscopic properties of the aggregate are reproduced using a simplified structural model of an extended aggregate, based on Frenkel Hamiltonian Calculations and on an estimate of the electronic couplings between each dimer composing the aggregate computed at DFT level.

Journal/Review: PHYSICAL CHEMISTRY CHEMICAL PHYSICS (PRINT)

Volume: 20 (34)      Pages from: 22331  to: 22341

More Information: This project has received funding from the European Union\’s Horizon 2020 research and innovation programme under grant agreement no. 654148 Laserlab-Europe, (Short: Laserlab-Europe, H2020 EC-GA 654148).
KeyWords: 2-dimensional electronic spectroscopy; Langmuir-Blodgett-films; sensitized solar-cells; photodynamic therapy; zinc phthalocyanine
DOI: 10.1039/c8cp02172d

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