Involving Synergy of Green Light and Acidic Responses in Control of Unimolecular Multicolor Luminescence

Abstract

Conversion of multicolor luminescence is one of desirable goals in study and development of next-generation molecular emitters, whereas involving visible light into the control of the above-mentioned ability has been poorly addressed due to the need of a relatively complicate molecular design. In this work, we present a novel dyad with a linkage of 4-piperazinyl-1,8-naphthalimide and cyanostyryl-modified azulene moiety, upon which the luminescence signal can be orthogonally controlled by protonation and green light irradiation. The superior features of the protonation induced excited state energy alteration, followed by green light driven photoisomerization led to a progressive luminescent color conversion among blue, yellow and green at the single molecular level. This strategy may bring in novel insights for preparing advanced function-integrated optoelectronic materials.

Proton‐Gated Ring‐Closure of a Negative Photochromic Azulene‐Based Diarylethene

“…In addition, protonation of o ‐ATE and deprotonation of c ‐ATE‐H + causes pronounced spectral changes, where the absorption edges of S 0 →S 1 transitions exhibit hypsochromic shifts in both cases by more than 120 nm (Figures a,b). These spectral shifts are considerably larger than those of the other proton‐responsive DAE‐type photoswitches using heteroatom‐based acid/base functional groups, which typically exhibit spectral shifts smaller than 50 nm upon protonation/deprotonation . Although proton‐response of azulene incorporated photoswitches has been sporadically reported, our 1 H NMR analyses convincingly suggest that the unique features of our system stem from protonation of the azulene moiety, which is directly incorporated in the photoreactive core.…”

“…These spectral shifts are considerably larger than those of the other proton‐responsive DAE‐type photoswitches using heteroatom‐based acid/base functional groups, which typically exhibit spectral shifts smaller than 50 nm upon protonation/deprotonation . Although proton‐response of azulene incorporated photoswitches has been sporadically reported, our 1 H NMR analyses convincingly suggest that the unique features of our system stem from protonation of the azulene moiety, which is directly incorporated in the photoreactive core. Most importantly, π‐conjugation between the tropylium moiety and the residual π‐system is strongly diminished after transformation of o ‐ATE‐H + into c ‐ATE‐H + (Figure c), giving rise to the negative photochromic ring‐closure that has not yet been reported for a regular DAE‐type photoswitch.…”

“…Thus far, azulene has rarely been employed in the skeleton of photoswitches, and their proton‐responsive photochromism was only sporadically studied in cyanostilbene‐type photoswitches . To unravel the full potential of the proton‐response of azulene in the development of novel multi‐stimuli responsive molecular photoswitches, here we describe the effect of incorporating azulene into the skeleton of a diarylethene‐type (DAE) photoswitch on its photochromic behavior.…”

Protonenvermittelter Ringschluss eines negativ photochromen, Azulen‐basierten Diarylethens

“…Deprotonierung aufweisen . Obwohl über die Protonensensitivität von Photoschaltern die Azulen enthalten, sporadisch berichtet wurde, zeigen unsere 1 H‐NMR‐Analysen deutlich, dass die einzigartigen Eigenschaften unseres Systems von der Protonierung der Azuleneinheit herrühren, welche unmittelbar im photoreaktiven Bereich lokalisiert ist. Am wichtigsten ist jedoch, dass die π‐Konjugation zwischen der Tropyliumeinheit und dem restlichen π‐System nach der Umwandlung von o ‐ATE‐H + in c ‐ATE‐H + stark vermindert ist (Abbildung c), was zu dem negativ photochromen Ringschluss führt, welcher für bisherige DAE‐Photoschalter nicht beobachtet wurde.…”

“…Bislang wurde Azulen nur selten als Teil des Gerüsts von Photoschaltern verwendet, und die protonensensitive Photochromie wurde nur vereinzelt bei Cyanostilben‐Photoschaltern untersucht . Um das volle Potenzial der Protonensensitivität von Azulen für die Entwicklung neuartiger molekularer Photoschalter zu entschlüsseln, wird nachfolgend der Einfluss des Einbaus in das Gerüst eines Diarylethen‐Photoschalters (DAE) untersucht.…”