Ultrafast investigation of photoinduced charge transfer in aminoanthraquinone pharmaceutical product

Song Zhang,Miaomiao Zhou,Lian Wang,Bing Zhang,Simei Sun

doi:10.1038/srep43419

Abstract

We investigated the mechanism of intramolecular charge transfer and the following radiationless dynamics of the excited states of 1-aminoanthraquinone using steady state and time-resolved absorption spectroscopy combined with quantum chemical calculations. Following photoexcitation with 460 nm, conformational relaxation via twisting of the amino group, charge transfer and the intersystem crossing (ISC) processes have been established to be the major relaxation pathways responsible for the ultrafast nonradiative of the excited S1 state. Intramolecular proton transfer, which could be induced by intramolecular hydrogen bonding is inspected and excluded. Time-dependent density functional theory (TDDFT) calculations reveal the change of the dipole moments of the S0 and S1 states along the twisted coordinate of the amino group, indicating the mechanism of twisted intra-molecular charge transfer (TICT). The timescale of TICT is measured to be 5 ps due to the conformational relaxation and a barrier on the S1 potential surface. The ISC from the S1 state to the triplet manifold is a main deactivation pathway with the decay time of 28 ps. Our results observed here have yield a physically intuitive and complete picture of the photoinduced charge transfer and radiationless dynamics in anthraquinone pharmaceutial products.

Highlights

We report on a joint experimental and calculational study of the excited-state dynamics of 1-aminoanthraquinone in solution after excitation to the charge transfer electronic state
The fast decay component of 5 ps is definitely attributed to twisted intramolecular charge transfer
We inspected the mechanism of intramolecular charge transfer and following radiationless dynamics of the excited states of 1-NH2-AQ using time-resolved absorption spectroscopy combined with quantum chemical calculations

Summary

Introduction

It is noticed that the O-H stretching vibration is at 2940 cm−1 to the red of the original band in the emission spectra and can be directly excited by the 400 nm pump pulse in Franck-Condon region. The dipole moment of the excited state, in which the -NH2 group is twisted, is obviously larger than that having the coplanar conformation. It is elucidated that the twisted intramolecular charge transfer is associated with the conformational relaxation on the potential surface of the S1 state.

Results

Conclusion