Design of High-Performance Pyridine/Quinoline Hydrazone Photoswitches

Abstract

Design of P-type photoswitches with thermal stability of the metastable form of hundreds of years that would efficiently transform using excitation wavelengths above 1 350 nm remains a challenge in the field of photochromism. In this regard, we designed and synthesized an extended set of 13 pyridine/quinoline hydrazones and systematically investigated the structure-property relationships defining their kinetic and photoswitching parameters. We show that the operational wavelengths of pyridine hydrazone structural motif can be effectively shifted towards the visible region without simultaneous loss of their high thermal stability. Furthermore, we characterized the ground state and excited state potential energy surfaces with quantum-chemical calculations and ultrafast transient absorption spectroscopy which allowed us to rationalize both the thermal and photochemical reaction mechanisms of the designed hydrazones. Whereas introducing an electron-withdrawing pyridyl moiety in benzoylpyridine hydrazones leads to thermal stabilities exceeding 200 years, extended π-conjugation in naphthoylquinoline hydrazones pushes the absorption maxima towards the visible spectral region. In either case, the compounds retain highly efficient photoswitching characteristics. Our findings open a route to rational design of a new family of hydrazone-based P-type photoswitches with high application potential in photonics or photopharmacology.

Hydrazone‐Based AIEgens with Photofluorochromic Ability for Rewritable, Intensity‐Variable, and High‐Resolution Photopattern

“…At the same time, TPAHPyMe failed to undergo such a process due to its more twisted conformation and the low mobility of the CN bond. [ 18 ] The photoisomerization of TPAHPy and TPAHB was further monitored by the 1 H NMR measurements (Figures S33 and S34, Supporting Information). The above results indicate that TPAHPy showing both sensitive photofluorochromism and excellent stability is highly desirable for serving as dynamic material for information storage and encryption.…”

The effect of resonance-assisted hydrogen bond on the second-order nonlinear optical properties of pyridine hydrazone photoswitches: a quantum chemistry investigation

“…The operational wavelengths of the pyridine hydrazone structural motif shifted toward the visible region without the accompanying loss of their high thermal stability, and hydrazone 7 retains good thermal stability. 25 Furthermore, the quantum-chemical calculations at the ωB97XD/def2-TZVPP level revealed a three-step inversion-rotation reaction mechanism of the thermal E -to- Z isomer. For benzoylpyridine hydrazones 1–8, 10, and 16, E -to- Z photoisomerization is more efficient compared to the Z -to- E process.…”

“…Recently, Mravec and collaborators 25–27 designed and synthesized an extended set of 13 pyridine/quinoline hydrazones photoswitches. This new class of hydrazone-based P-type photoswitches is switchable between two isomers Z and E (see Fig.…”

“…For benzoylpyridine hydrazones 1–8, 10, and 16, E -to- Z photoisomerization is more efficient compared to the Z -to- E process. From the work of Mravec et al , 25 we can note that these compounds could be used for short-lived and long-lived information storage, 28 and these isomers could be utilized as photoswitch molecules.…”

“…In our work, we studied a series of 18 pyridine hydrazone photoswitches ( Zi and Ei isomers, i = 1–18, see Fig. 1), which is divided in two subgroups, namely, one group of ten Zi and Ei isomers (where i = 1–8, 10, and 16) synthesized by Mravec et al 25 and another one we designed, consisting of eight compounds ( i = 9, 11–15, and 17–18 of Ei and Zi isomers), to investigate the substitutional effect on the hydrazine and ketone parts on the structural, electronic, reactivity, optical properties, and nonlinear responses. On ring 2, we chose two electron-withdrawing (EW) namely NO 2 and CN in order to study the effect of the EW character on electronic and optical properties.…”