How the nitro group position determines the emission properties of ?-expanded diketopyrrolopyrroles
Year: 2025
Authors: Skonieczny K., Di Maiolo F., Venturi S., Iagatti A., Ricci A., Bertocchi F., Gryko D.T., Lapini A.
Autors Affiliation: Polish Acad Sci, Inst Organ Chem, Kasprzaka 44-52, PL-01224 Warsaw, Poland; LENS European Lab Nonlinear Spect, Via N Carrara 1, I-5001 Sesto Fiorentino, Italy; Univ Parma, Dept Chem Life Sci & Environm Sustainabil, Parco Area Sci 17-A, I-43124 Parma, Italy; Ist Nazl Ott CNR CNR INO, Via Nello Carrara 1, I-50019 Sesto Fiorentino, Italy.
Abstract: Two complex pi-expanded diketopyrrolopyrroles (EDPPs) have been prepared following a multistep but straightforward strategy. We discovered that the fate of these molecules in the excited state can be controlled by subtle differences in their structure. When NO2 groups are located at a distant position, the quadrupolar, centrosymmetric dye exhibits strong red emission across the solvents’ polarity scale. However, when NO2 groups are adjacent to the lactam moiety, the EDPPs exhibit negligible emission even in non-polar solvents. Density functional theory (DFT) calculations indicate that the primary distinction between the two molecules lies in the structural planarity. The molecule with NO2 groups adjacent to the lactam moiety exhibits a loss of planarity due to the coulombic repulsion between these groups. The calculations also suggest that the nitro group does not participate in the S0 -> S1 excitation. Furthermore, for both compounds, the first two excited states (one bright and one dark) are found to be very close in energy. The change in molecular geometry affects the non-radiative deactivation of excited states, leading to the two distinct emission behaviors. Experiments in a glassy solvent at low temperatures reveal that at 77 K the photophysics of both dyes becomes the same, which proves that thermal activation is the key mechanism for the non-radiative decay of the excited state for non-emissive EDPPs.
Journal/Review: PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume: 27 (12) Pages from: to:
More Information: The work was financially supported by the Polish National Science Center, Poland (OPUS 2020/37/B/ST4/00017) and the Foundation for Polish Science (TEAM POIR.04.04.00-00-3CF4/16-00). The support from the Italian Ministry of Research through the project 20225NPY8P (LANTERN), through the project P2022ALSMP_002 (VISIO) and the IPHOQS project is acknowledged. The support from Parma University through the project SFM-CARS is also gratefully acknowledged. F. D. M. acknowledges financial support from Bando di ateneo per la ricerca 2023 – azione B. This work benefited from the support of the HPC (High Performance Computing) facility at the University of Parma. F. D. M. acknowledges the CINECA award under the ISCRA initiative, for the availability of high-performance computing resources and support (project IsCb8 InveST (HP10CIDH42)). F. D. M. position was co-funded by the European Union – PON Research and Innovation 2014-2020. AL would like to acknowledge Alessio Montori from LENS Electronic Workshop for his contribution to the development of the experimental signal acquisition. We thank N. D. G. for amending the manuscript.KeyWords: Pyrrolopyrrole Aza-bodipy; Internal-conversion; Molecular Design; Triplet-states; Fluorescence; Absorption; Analogs; Photochemistry; Photophysics; MechanismDOI: 10.1039/d4cp04689g
