Control of the Photo-Isomerization Mechanism in 3 H -Naphthopyrans to Prevent Formation of Unwanted Long-Lived Photoproducts

• Published in: International journal of molecular sciences Vol. 21; no. 21
• Main Authors: Brazevic, Sabina, Nizinski, Stanisław, Sliwa, Michel, Abe, Jiro, Rode, Michał F, Burdzinski, Gotard
• Format: Journal Article
• Language: English
• Published: Switzerland 22-10-2020
• Subjects: Absorptiometry, Photon; Benzopyrans - chemistry; Isomerism; Models, Chemical; Photochemical Processes; Spectrophotometry, Ultraviolet; time-resolved spectroscopy; photochromism; photodynamics; quantum chemical calculations; reaction mechanisms; photophysics; bicycle-pedal isomerization; naphthopyran
• ISSN: 1422-0067

In the photochromic reactions of 3
-naphthopyrans, two colored isomers TC (transoid-
) and TT (transoid-
) are formed. In terms of optimized photo-switchable materials, synthetic efforts are nowadays evolving toward developing 3
-naphthopyran derivatives that would not be able to photoproduce the long-living transoid-
, TT, photoproduct. The substitution with a methoxy group at position 10 results in significant reduction of the TT isomer formation yield. The TC photophysics responsible for TT suppression were revealed here using a combination of multi-scale time resolved absorption UV-vis spectroscopy and ab initio calculations. The substitution changes the TC excited-state potential energy landscape, the
isomerization path is favored over the rotation around a single double bond. The
path is aborted in halfway to TT formation due to S
→S
internal conversion populating back the TC species in the ground electronic state. This is validated by a shorter TC S
state lifetime for methoxy derivative in comparison to that of the parent-unsubstituted compound (0.47 ± 0.05 ps vs. 0.87 ± 0.09 ps) in cyclohexane.