Distinct Excited-State Dynamics of Near-Orthogonal Perylenimide Dimer: Conformational Planarization versus Symmetry Breaking Charge Transfer

Abstract

Efficient photoinduced charge separation in artificial multichromophoric architectures relies on two critical factors, (i) electronic coupling and (ii) solvation. While the coherent exciton interactions delocalize the excitation energy among molecules, the solvation-dependent dynamical disorder tends to localize it. Local environments such as solvent polarity/dielectric environments exhibit profound effect on mediating the excited-state relaxation dynamics via specific electronic/geometric changes in chromophore multimers. Herein, a comprehensive account of the solvent governed distinct exciton coupling and symmetry breaking charge separation in a near-orthogonal perylenimide dimer (PP) is presented employing steady-state, femtosecond transient absorption measurements and quantum chemical calculations. Steady-state absorption measurements of the PP dimer reveal apparent electronic coupling between the two monomeric units, wherein the fluorescence measurements reveal a strong fluorescence character in nonpolar solvent, but a significantly quenched state is observed in polar solvent. Ultrafast transient absorption measurements reveal that the fluorescence quenching in polar solvent arises from a photoinduced symmetry-breaking charge transfer (SBCT) process and a subsequent population of the charge-separated radical ion-pair state. Contrastingly, in nonpolar solvent, the charge transfer is endothermic and energetically not feasible. Manifestly, the dimer in nonpolar solvent undergoes a conformational planarization within 20 ps accompanied by excitation delocalization over the two identical monomers in the lowest excited singlet state as evident from the dominant stimulated emission (around 580 nm) and the excited-state absorption (around 740 nm) in the femtosecond transient absorption spectra. Observed solvent-mediated selective control on the excited-state relaxation pathways in the near-orthogonal PP dimer can help shed light on the mechanisms of energy/charge transfer in molecular systems and guide the design of novel high-performance photovoltaic materials.

Linker dependent symmetry breaking charge separation in 9,10-bis(phenylethynyl)anthracene dimers

“…However, to date, for most SB-CS materials, SB-CS only could proceed in polar solvents, and the recombination rate of the CS state is also fast. 11–18 This is disadvantageous for applying SB-CS materials in organic solar cells for improving the photoelectric conversion efficiency. Thus, developing new SB-CS materials with faster rates and slow recombination in nonpolar or weakly polar solvents is urgent for its practical application in organic solar cells.…”

Excited State Dynamics of Perylenediimide films with Isopropyl phenyl- and Undecane-Substitution

“…Besides, the relaxation of ESA at 625 nm is seen to develop from positive magnitude to negative one, which manifests the formation of excimer-like state after photoexcitation. 28 The magnitude of A at 625 nm is resulted from the superposition of excited state absorption and excimer-like emission. The lifetime of the excimer in PDI-1 film is about 14.8 ns as determined from TRPL measurement shown in Fig.…”

“…. The absorption and PL spectra of both PDIs in 10 -5 M chloroform solution show exact the same, in which absorption bands are located around 526, 489, and 458 nm for 0−0, 0−1, and 0−2 vibronic bands, respectively.While the PL spectrum shows clear mirror symmetry with the absorption band, in which the 0−0, 0−1, and 0−2 vibronic emission bands are located around 533, 573 and 620 nm, respectively28 . As mentioned above, the imide-substituent of PDI in dilute solution has negligible effect on optical properties.…”

Perylene Monoimide as a Versatile Fluoroprobe: The Past, Present, and Future

“…To shed light on PMI-based symmetry breaking charge transfer (SBCT), Hariharanʼs group came up with a PMI dimer model where two PMI monomers were directly connected with an orthogonal orientation between them. 48 The PMI dimer (133) exhibited fluorescence quenching (φ F = 0.21) in polar solvent acetonitrile (ACN) which is attributable to photoinduced SBCT, as depicted in Figure 23.…”

“…Both 124 and 125 achieve a photoconversion efficiency (η) Introduction of sulphur as a heteroatom in addition to nitrogen has also been utilized for peri-functionalization (as shown in Figure 53). All of the aforementioned dyes (48,49,50) are classical push-pull systems showing different degrees of orbital partitioning. This orbital partitioning mainly results from the different degrees of twisting induced into the system by various donors.…”