Directly Linked Zinc Phthalocyanine-Perylenediimide Dyads and a Triad for Ultrafast Charge Separation

Solvent effects on the photoinduced charge separation dynamics of directly linked zinc phthalocyanine-perylenediimide dyads: a nonadiabatic dynamics simulation with an optimally tuned screened range-separated hybrid functional

Herein, we have employed a combination of the optimally tuned screened range-separated hybrid (OT-SRSH) functional, the polarizable continuum model (PCM), and nonadiabatic dynamics (NAMD) simulations to investigate the photoinduced dynamics of directly linked donor-acceptor dyads formed using zinc phthalocyanine (ZnPc) and perylenediimide (PDI), in which ZnPc is the donor while PDI is the acceptor. Our simulations aim to analyze the behavior of these dyads upon local excitation of the ZnPc moiety in the gas phase and in benzonitrile. Our findings indicate that the presence of a solvent can significantly influence the excited state dynamics of ZnPc-PDI dyads. Specifically, the polar solvent benzonitrile effectively lowers the vertical excitation energies of the charge transfer (CT) state from ZnPc to PDI. As a result, the energetic order of the locally excited (LE) states of ZnPc and the CT states is reversed compared to the gas phase. Consequently, the photoinduced electron transfer (PET) dynamics from ZnPc to PDI, which is absent in the gas phase, takes place in benzonitrile with a time constant of 10.4 ps. Importantly, our present work not only qualitatively agrees with experimental results but also provides in-depth insights into the underlying mechanisms responsible for the photoinduced dynamics of ZnPc-PDI. Moreover, this study emphasizes the importance of appropriately considering solvent effects in NAMD simulation of organic donor-acceptor systems, taking into account the distinct excited state dynamics observed in the gas phase and benzonitrile. Furthermore, the combination of the OT-SRSH functional, the PCM solvent model, and nonadiabatic dynamics simulations shows promise as a strategy for investigating the complex excited state dynamics of organic donor-acceptor systems in solvents. These findings will be valuable for the future design of novel organic donor-acceptor structures with improved performance.

Panchromatic Light-Capturing Bis-styryl BODIPY-Perylenediimide Donor-Acceptor Constructs: Occurrence of Sequential Energy Transfer Followed by Electron Transfer

Two wide-band-capturing donor-acceptor conjugates featuring bis-styrylBODIPY and perylenediimide (PDI) have been newly synthesized, and the occurrence of ultrafast excitation transfer from the 1 PDI* to BODIPY, and a subsequent electron transfer from the 1 BODIPY* to PDI have been demonstrated. Optical absorption studies revealed panchromatic light capture but offered no evidence of ground-state interactions between the donor and acceptor entities. Steady-state fluorescence and excitation spectral recordings provided evidence of singlet-singlet energy transfer in these dyads, and quenched fluorescence of bis-styrylBODIPY emission in the dyads suggested additional photo-events. The facile oxidation of bis-styrylBODIPY and facile reduction of PDI, establishing their relative roles of electron donor and acceptor, were borne out by electrochemical studies. The electrostatic potential surfaces of the S1 and S2 states, derived from time-dependent DFT calculations, supported excited charge transfer in these dyads. Spectro-electrochemical studies on one-electron-oxidized and one-electron-reduced dyads and the monomeric precursor compounds were also performed in a thin-layer optical cell under corresponding applied potentials. From this study, both bis-styrylBODIPY⋅+ and PDI⋅- could be spectrally characterizes and were subsequently used in characterizing the electron-transfer products. Finally, pump-probe spectral studies were performed in dichlorobenzene under selective PDI and bis-styrylBODIPY excitation to secure energy and electron-transfer evidence. The measured rate constants for energy transfer, kENT , were in the range of 1011  s-1 , while the electron transfer rate constants, kET , were in the range of 1010  s-1 , thus highlighting their potential use in solar energy harvesting and optoelectronic applications.

Synthesis of a new zinc phthalocyanine–benzoquinone rigid dyad

A new zinc phthalocyanine–benzoquinone rigid dyad, QnZnPc–G[Formula: see text] was synthesized as a model compound to study photo-induced charge separation mimicking natural photosynthesis. Compared to its previously reported analog, this dyad has an additional fused benzene ring between the zinc phthalocyanine (ZnPc) (donor) and benzoquinone (acceptor) moieties. The rigid structure of QnZnPc–G[Formula: see text] ([Formula: see text] no rotamers) is designed to minimize the unusual electronic perturbation induced by the internal motions, which resulted in a significant increase in the lifetime of the charged separated state (from 40 ps to 252 ps). Physical and photochemical properties of this new dyad were examined and discussed in this paper.

Efficacious elimination of intramolecular charge transfer in perylene imide based light-harvesting antenna molecules

Two light-harvesting antenna molecules were obtained by positioning naphthalene monoimide energy donors at the imide position, instead of the bay positions, of perylene imide energy acceptors. Such rational design resulted in a complete suppression of parasitic intramolecular charge transfer without compromising the desired ultrafast rates of excitation energy transfer.

Squaraine Dyes: Molecular Design for Different Applications and Remaining Challenges

Squaraine dyes are a class of organic dyes with strong and narrow absorption bands in the near-infrared. Despite high molar absorptivities and fluorescence quantum yields, these dyes have been less explored than other dye scaffolds due to their susceptibility to nucleophilic attack. Recent strategies in probe design including encapsulation, conjugation to biomolecules, and new synthetic modifications have seen squaraine dyes emerging into the forefront of biomedical imaging and other applications. Herein, we provide a concise overview of (1) the synthesis of symmetrical and unsymmetrical squaraine dyes, (2) the relationship between structure and photophysical properties of squaraine dyes, and (3) current applications of squaraine dyes in the literature. Given the recent successes at overcoming the limitations of squaraine dyes, they show high potential in biological imaging, in photodynamic and photothermal therapies, and as molecular sensors.

A zinc phthalocyanine–benzoperylenetriimide conjugate for solvent dependent ultrafast energy vs. electron transfer

Ultrafast energy and electron transfer as a function of solvent polarity has been demonstrated using a femtosecond transient absorption technique in a zinc phthalocyanine–benzoperylenetriimide conjugate.