Intramolecular Charge Transfer of 1-Aminoanthraquinone and Ultrafast Solvation Dynamics of Dimethylsulfoxide.

Kooknam Jeon,Myungsam Jen,Sebok Lee,Yoonsoo Pang,Taehyung Jang

doi:10.3390/ijms222111926

Abstract

The intramolecular charge transfer (ICT) of 1-aminoanthraquinone (AAQ) in the excited state strongly depends on its solvent properties, and the twisted geometry of its amino group has been recommended for the twisted ICT (TICT) state by recent theoretical works. We report the transient Raman spectra of AAQ in a dimethylsulfoxide (DMSO) solution by femtosecond stimulated Raman spectroscopy to provide clear experimental evidence for the TICT state of AAQ. The ultrafast (~110 fs) TICT dynamics of AAQ were observed from the major vibrational modes of AAQ including the νC-N + δCH and νC=O modes. The coherent oscillations in the vibrational bands of AAQ strongly coupled to the nuclear coordinate for the TICT process have been observed, which showed its anharmonic coupling to the low frequency out of the plane deformation modes. The vibrational mode of solvent DMSO, νS=O showed a decrease in intensity, especially in the hydrogen-bonded species of DMSO, which clearly shows that the solvation dynamics of DMSO, including hydrogen bonding, are crucial to understanding the reaction dynamics of AAQ with the ultrafast structural changes accompanying the TICT.

Highlights

Since the ultrafast charge transfer processes are often observed in natural photosynthesis with the utmost quantum efficiency, optimal molecular structures for efficient intramolecular charge transfer (ICT) processes have been of great importance for the dyes and sensitizers adopted in various applications including for organic light-emitting devices, photovoltaics, solar cells, etc. [1,10,11,12,13]
We report that the excitedstate dynamics investigation by FSRS may provide important experimental results for the understanding of chemical reaction dynamics in the liquid phase
The absorption maximum of AAQ appears at 485 nm in a polar DMSO solution

Summary

Introduction

Charge transfer has been considered as one of the fundamental photoinduced processes in many chemical and biological systems including oxidation and reduction reactions and natural photosynthesis [1,2,3,4,5,6]. Intramolecular charge transfer (ICT), as one of the model systems for charge transfer, has been extensively studied experimentally and theoretically, whereby the electron donor and acceptor groups are connected by a single chemical bond or π-bridge [7,8,9]. Since the ultrafast charge transfer processes are often observed in natural photosynthesis with the utmost quantum efficiency, optimal molecular structures for efficient ICT processes have been of great importance for the dyes and sensitizers adopted in various applications including for organic light-emitting devices, photovoltaics, solar cells, etc. Ultrafast structural evolutions of chromophores during the ICT processes, such as the twisted ICT (TICT) or planar ICT (PICT) state in the excited states have been investigated by many time-resolved electronic or vibrational spectroscopy and time-dependent density functional theory (TDDFT) simulations [9,14,15,16,17]

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Conclusion