Photochromic nucleic base units suitable for nucleic acid labelling

Refined Insights in the Photochromic spiro-Dihydroindolizine/Betaine System

We have revisited the photochromic spiro-dihydroindolizine/betaine system by comparing state-of-the-art density functional theory calculations with experimental data. Time-dependent density functional theory calculations are employed to examine the transformations occurring after photoexcitation. This study confirms that photoexcitation of the spiro-dihydroindolizine leads to the formation of the cis-betaine. However, isomerization to the trans-betaine follows through a complicated and formerly unknown potential energy landscape, which consists of a network of transition states and intermediates. The available pathways across this potential energy landscape will determine the kinetics of the forward reaction from the cis-betaine to the trans-betaine and then, even more importantly, the back-reaction. Virtually all practical applications of this optical switch rely on these reactions and, therefore, occur within this landscape. Predicting the network of transition states and intermediates for substituted spiro-dihydroindolizine/betaine systems will enable the in-silico design of optical switches with enhanced performance.

Molecular switches as photocontrollable "smart" receptors

This critical review focuses on the development of photochromic compounds as sensors for cations, anions, and biologically important molecules. The review commences with a brief description of photochromism and the strategies to exploit photochromic molecular switches' properties for sensing application. This is followed by a summary of photoswitchable receptors emerged to date and classified according to the photochromic structure they are based on. These include azobenzenes, fulgides, dithienylethenes, dihydroindolizines, chromenes and spiropyrans.

Photoinduced ring-opening of a photochromic dihydroindolizine derivative monitored with femtosecond visible and infrared spectroscopy

We present results of a femtosecond spectroscopy study of the ring-opening dynamics of the photochromic compound trimethyl-1'H-spiro[fluorene-9,1'-pyrrolo[1,2-b]pyridazines]-2',3',6'-tricarboxylate (also known as dihydroindolizine and abbreviated as DHI) in solvents of different polarities. We follow the ring-opening dynamics of photoexcited DHI by probing the transient response in the visible region between 450 and 700 nm, as well as in the fingerprint region between 1100 and 1800 cm(-1). We conclude that photoexcited DHI converts into the ring-opened betaine isomer while remaining in the electronic excited state. Subsequent electronic excited-state decay on a time scale of 40-80 ps results in regeneration of ground-state DHI (0.75-0.9 quantum yield) or betaine photoproduct, the exact value for DHI quantum yield recoveries and rates being solvent dependent.