Ultrafast Structure and Vibrational Dynamics of a Cyano-Containing Non-Fullerene Acceptor for Organic Solar Cells Revealed by Two-Dimensional Infrared Spectroscopy

Abstract

thiophene), are among the most promising non-fullerene acceptors for organic solar cells (OSCs). In this work, using the cyano stretching mode as a vibrational marker, the structural and vibrational energy dynamics of ITIC were examined on an ultrafast time scale with two-dimensional infrared spectroscopy. Two IR-active modes studied here mainly correspond to two anti-symmetric combinations of symmetric and asymmetric stretching vibrations of two CN modes originating from two −C(CN) 2 chromophores that are located across the ITIC system, which were found to have significantly larger off-diagonal anharmonicity than their corresponding diagonal anharmonicities. This indicates strong anharmonic vibrational coupling between the two modes, which is supported by ab initio anharmonic frequency computations. Transient IR results indicate picosecond intramolecular vibrational energy transfer between the two CN modes upon excitation. The structural basis for these vibrational and energetic features is the conjugating molecular frame that is composed of a network of single/double bonds connecting the two −C(CN) 2 chromophores and may enable efficient vibration delocalization, in addition to its well-known electron delocalization capability. The importance of the results for the OSC applications is discussed.

Triple-Bond Vibrations: Emerging Applications in Energy and Biological Sciences

“…Likewise, Yutaka and co-workers took advantage of the sensitivity of the CN stretching vibration to the electron density around the nitrile triple bond and used it to study the photoexcited dynamics of two different OPV acceptors, TT-FT-DCI (Figure , (11)) and TT-T-DCI (Figure , (12)). Moreover, the CN stretching vibrational mode has been employed to assess the structure and dynamics of various energy-related molecules and systems via two-dimensional IR (2D IR) spectroscopy. − …”

Charge Transfer Dynamics in Organic–Inorganic Hybrid Heterostructures—Insights by Vibrational‐Sum Frequency Generation Spectroscopy

“…For example, 2D‐IR measurements on ITIC (3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene) indanone)‐5,5,11,11‐tetrakis (4‐hexylphenyl) dithieno [2,3‐d : 2′,3′‐d′]‐s‐indaceno [1,2‐b : 5,6‐b′]‐dithiophene, a promising non‐fullerene acceptor for organic solar cells, revealed strong anharmonic vibrational coupling between two distinct C≡N vibrational modes arising from two −C(CN) 2 chromophores located across the ITIC system. The respective C≡N oscillators efficiently exchange vibrational energy within the conjugated molecular frame as evidenced by time‐resolved measurements [16b] …”

Ladungstransferdynamiken in organisch–anorganischen hybriden Heterostrukturen – Einblicke mithilfe von Summenfrequenzspektroskopie

“…Diese Schwingungsmoden stammen von zwei −C(CN) 2 ‐Chromophoren, welche sich im ITIC‐System befinden. Die entsprechenden C≡N‐Oszillatoren tauschen, wie zeitaufgelöste Messungen zeigen, effizient Schwingungsenergie innerhalb des konjugierten Bereichs des Moleküls aus [16b] …”