Photophysical and Electrochemical Characterization of BODIPY-Containing Dyads Comparing the Influence of an A–D–A versus D–A Motif on Excited-State Photophysics

Abstract

A complete photophysical characterization of organic molecules designed for use as molecular materials is critical in the design and construction of devices such as organic photovoltaics (OPV). The nature of a molecule's excited state will be altered in molecules employing the same chromophoric units but possessing different molecular architectures. For this reason, we examine the photophysical reactions of two BODIPY-based D-A and A-D-A molecules, where D is the donor and A is the acceptor. A BODIPY (4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene) moiety serves as the A component and is connected through the meso position using a 3-hexylthiophene linker to a N-(2-ethylhexyl)dithieno[3,2-b:2',3'-d]pyrrole (DTP), which serves as the D component. An A-D-A motif is compared to its corresponding D-A dyad counterpart. We show a potential advantage to the A-D-A motif over the D-A motif in creating longer-lived excited states. Transient absorption (TA) spectroscopy is used to characterize the photophysical evolution of each molecule's excited state. Global analysis of TA data using singular value decomposition and target analysis is performed to identify decay-associated difference spectra (DADS). The DADS reveal the spectral features associated with charge-transfer excited states that evolve with different dynamics. A-D-A possess slightly longer excited-state lifetimes, 42 ps nonradiative decay, and 4.64 ns radiative decay compared to those of D-A, 24 ps nonradiative decay, and 3.95 ns radiative decay. A longer lived A-D-A component is observed with microsecond lifetimes, representing a small fraction of the total photophyscial product. Steady-state and time-resolved photoluminescence augment the insights from TA, while electrochemistry and spectroelectrochemistry are employed to identify the nature of the excited state. Density functional theory supports the observed electronic and electrochemical properties of the D-A and A-D-A molecules. These results form a complete picture of the electronic and photophysical properties of D-A and A-D-A and provide contextualization for structure-function relationships between molecules and OPV devices.

σ-Pt-BODIPY Complexes with Platinum Attachment to Carbon Atoms C2 or C3: Spectroscopic, Structural, and (Spectro)Electrochemical Studies and Photocatalysis

“…90 The latter are of great interest with respect to light-to-energy conversion schemes or mimicking natural enzymes. 85,87,90,92,93 The results of our voltammetric studies on the σ-platinum bodipy complexes are summarized in Table 6. In their cyclic voltammograms, all complexes except for 8-Pt show a fully or nearly reversible one-electron oxidation and a reversible to partially reversible reduction within the electrochemical window of the CH 2 Cl 2 /NBu 4 PF 6 supporting electrolyte (see Figures 7 and 8).…”

“…The results of these studies can serve as reference points for our present results. 84,85,87,89,91,92,94,95 Like for the other studies, the radical cations or anions were generated inside a transparent UV/vis/NIR cell 96 or inside an EPR tube under the in situ conditions of spectroelectrochemistry. The results of these studies are displayed in Figures 9 and S61−S63, while Table 7 summarizes the relevant data and the TD-DFT calculated band energies and assignments.…”

“…This again agrees with previous studies on other bodipys. 87,88,94,95 TD-DFT calculations suggest that the NIR absorption of the 2-Pt-Mes-6I radical cation originates from a mixed ILCT (Mes → bodipy) and PtI → bodipy ML → L′CT transition at 1162 nm and at 805 nm with CT from the iodo and mesityl substituents to the bodipy π system (see Figures S66 and S67 and Table 7). Owing to the presence of multiple nuclei with a nuclear spin I ≠ 0, and the fundamental differences between ligand-and metal-centered spin, EPR spectroscopy provides another potent tool to probe for the identity of the respective redox site.…”

Side chain engineering on dithieno[3,2-b:2,3-d]pyrrol fused electron acceptors for efficient organic solar cells

“…Tetrahydrofuran (THF) and toluene were distilled from sodium before use, and 1,2dichloroethane was dried with calcium hydride. 33 INPIC-EH. Under the protection of argon, Compound 5a (150.0 mg, 108.85 μmol), 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1ylidene) malononitrile (200.43 mg, 807.76 μmol) and β-alanine (1.80mg, 20.20 μmol) was dissolved in a mixture of ClCH2CH2Cl and EtOH (8 mL/4 mL).…”

BODIPY dyads and triads: synthesis, optical, electrochemical and transistor properties

“…The effect of BODIPY structures on photophysical properties has been intensively explored [ 10 , 13 ], while fundamental understanding on relationship between structures and charge transport property is less investigated. Generally, BODIPY based small molecules have been designed using symmetrical D–A–D and A–D–A triads [ 15 , 16 ], where donor (D) is an electron rich functionality and acceptor (A) is a BODIPY unit. For instances, Krishnamoothy et al [ 17 ] studied the effect of alkyl side chains at the meso -position of triphenylamine-BODIPY-triphenylamine triads on the charge transport properties.…”