Universität zu Köln

Bernhardt, Robin ORCID: 0000-0002-0296-8731, Manrho, Marick ORCID: 0000-0001-5165-8345, Zablocki, Jennifer ORCID: 0000-0002-2100-4807, Rieland, Lukas, Lutzen, Arne, Schiek, Manuela ORCID: 0000-0002-0108-2998, Meerholz, Klaus, Zhu, Jingyi ORCID: 0000-0003-0519-4724, Jansen, Thomas L. C., Knoester, Jasper and van Loosdrecht, Paul H. M. (2022). Structural Disorder as the Origin of Optical Properties and Spectral Dynamics in Squaraine Nano-Aggregates. J. Am. Chem. Soc., 144 (42). S. 19372 - 19382. WASHINGTON: AMER CHEMICAL SOC. ISSN 1520-5126

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Abstract

In contrast to regular J- and H-aggregates, thin film squaraine aggregates usually have broad absorption spectra containing both J-and H-like features, which are favorable for organic photovoltaics. Despite being successfully applied in organic photovoltaics for years, a clear interpretation of these optical properties by relating them to specific excited states and an underlying aggregate structure has not been made. In this work, by static and transient absorption spectroscopy on aggregated n-butyl anilino squaraines, we provide evidence that both the red- and blue-shifted peaks can be explained by assuming an ensemble of aggregates with intermolecular dipole-dipole resonance interactions and structural disorder deriving from the four different nearest neighbor alignments-in sharp contrast to previous association of the peaks with intermolecular charge-transfer interactions. In our model, the next-nearest neighbor dipole-dipole interactions may be negative or positive, which leads to the occurrence of J- and H-like features in the absorption spectrum. Upon femtosecond pulse excitation of the aggregated sample, a transient absorption spectrum deviating from the absorbance spectrum emerges. The deviation finds its origin in the excitation of two-exciton states by the probe pulse. The lifetime of the exciton is confirmed by the band integral dynamics, featuring a single-exponential decay with a lifetime of 205 ps. Our results disclose the aggregated structure and the origin of red- and blue-shifted peaks and explain the absence of photoluminescence in squaraine thin films. Our findings underline the important role of structural disorder of molecular aggregates for photovoltaic applications.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Bernhardt, Robin UNSPECIFIED orcid.org/0000-0002-0296-8731 UNSPECIFIED Manrho, Marick UNSPECIFIED orcid.org/0000-0001-5165-8345 UNSPECIFIED Zablocki, Jennifer UNSPECIFIED orcid.org/0000-0002-2100-4807 UNSPECIFIED Rieland, Lukas UNSPECIFIED UNSPECIFIED UNSPECIFIED Lutzen, Arne UNSPECIFIED UNSPECIFIED UNSPECIFIED Schiek, Manuela UNSPECIFIED orcid.org/0000-0002-0108-2998 UNSPECIFIED Meerholz, Klaus UNSPECIFIED UNSPECIFIED UNSPECIFIED Zhu, Jingyi UNSPECIFIED orcid.org/0000-0003-0519-4724 UNSPECIFIED Jansen, Thomas L. C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Knoester, Jasper UNSPECIFIED UNSPECIFIED UNSPECIFIED van Loosdrecht, Paul H. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-689053
DOI:	10.1021/jacs.2c07064
Journal or Publication Title:	J. Am. Chem. Soc.
Volume:	144
Number:	42
Page Range:	S. 19372 - 19382
Date:	2022
Publisher:	AMER CHEMICAL SOC
Place of Publication:	WASHINGTON
ISSN:	1520-5126
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language EXCITON DELOCALIZATION; ELECTRONIC-STRUCTURE; 2-PHOTON ABSORPTION; ENERGY-TRANSFER; J-BAND; DYES; SPECTROSCOPY; CHEMISTRY; BEHAVIOR; MECHANISMS Multiple languages Chemistry, Multidisciplinary Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/68905