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Low-lying excited states in crystalline perylene.

ABSTRACT: Organic materials are promising candidates for advanced optoelectronics and are used in light-emitting diodes and photovoltaics. However, the underlying mechanisms allowing the formation of excited states responsible for device functionality, such as exciton generation and charge separation, are insufficiently understood. This is partly due to the wide range of existing crystalline polymorphs depending on sample preparation conditions. Here, we determine the linear optical response of thin-film single-crystal perylene samples of distinct polymorphs in transmission and reflection geometries. The sample quality allows for unprecedented high-resolution spectroscopy, which offers an ideal opportunity for judicious comparison between theory and experiment. Excellent agreement with first-principles calculations for the absorption based on the GW plus Bethe-Salpeter equation (GW-BSE) approach of many-body perturbation theory (MBPT) is obtained, from which a clear picture of the low-lying excitations in perylene emerges, including evidence of an exciton-polariton stopband, as well as an assessment of the commonly used Tamm-Dancoff approximation to the GW-BSE approach. Our findings on this well-controlled system can guide understanding and development of advanced molecular solids and functionalization for applications.

SUBMITTER: Rangel T

PROVIDER: S-EPMC5777036 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Low-lying excited states in crystalline perylene.

Rangel Tonatiuh T Rinn Andre A Sharifzadeh Sahar S da Jornada Felipe H FH Pick André A Louie Steven G SG Witte Gregor G Kronik Leeor L Neaton Jeffrey B JB Chatterjee Sangam S

Proceedings of the National Academy of Sciences of the United States of America 20171226 2

Organic materials are promising candidates for advanced optoelectronics and are used in light-emitting diodes and photovoltaics. However, the underlying mechanisms allowing the formation of excited states responsible for device functionality, such as exciton generation and charge separation, are insufficiently understood. This is partly due to the wide range of existing crystalline polymorphs depending on sample preparation conditions. Here, we determine the linear optical response of thin-film ...[more]

PMID: 29279373

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Project description:A family of complexes of the type [Ru(tpbn)(IP-R)(4-pic)]Cl2 (tbpn=2,2'-(4-(tert-butyl)pyridine-2,6-diyl)bis(1,8-napthyridine); 4-pic=4-picoline; IP-R=imidazo[4,5-f][1,10]phenanthroline attached to an aromatic group R for 2-8 and H for 1) were prepared as near-infrared (NIR) absorbing coordination complexes to test whether triplet intraligand excited states (3IL) of higher energy than the lowest-lying triplet metal-to-ligand charge transfer excited states (3MLCT) could effectively generate cytotoxic singlet oxygen (1O2) and elicit in vitro photodynamic therapy (PDT) effects. Aromatic groups ranged from benzene to anthracene, with corresponding triplet state energies that were all significantly higher (approximately 3.7-1.8 eV) than the 3MLCT state estimated at 1.5 eV. Complexes 1-8 absorbed NIR light, with their longest-wavelength peak maxima occurring near 725 nm that extended out to 800 nm. The 1O2 quantum yields for the aromatic-containing compounds were extremely small (ΦΔ=0.07), with correspondingly modest in vitro photocytotoxicities. All compounds were nontoxic without a light trigger, with dark EC50 values >60 μM and most values closer to 100 or greater. EC50 values with visible light were 5-6 (PI=15-20), 7-10 (PI=8-11), and 10-15 μM (PI=6-8) in SKMEL28, A375, and B16F10 cancer cell lines, respectively. With NIR light, these values were even less: 11-16 (PI=5-9), 16-50 (PI=2-6), and 15-19 μM (PI=4-6) in SKMEL28, A375, and B16F10 cancer cell lines, respectively. While measurable, the modest activities and absence of any trend between the 3IL energies and values for ΦΔ or PI demonstrate that 3IL states with energies above the lowest-lying 3MLCT states do not contribute to the overall excited state dynamics responsible for potent PDT effects in previous studies. Lowest-lying 3MLCT states in this family of NIR-absorbing photosensitizers do not produce the requisite 1O2 for effective in vitro photocytotoxic effects, underscoring the need to install 3IL states that are lower in energy than the lowest-lying 3MLCT states in order the create potent NIR-activatable Ru(II) complexes for PDT.

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Low-lying excited states in crystalline perylene.

Publications

Low-lying excited states in crystalline perylene.

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