Photochemistry of Photochromic Benzopyrans Studied by Time-Resolved Absorption Spectroscopy

Abstract

generated open forms gives rise to other open forms that need a doublebond rotation for reversion to the original closed form. Such a two-step two-photon photochromism can be expected to have a wide range of application.

Photophysics and kinetics of naphthopyran derivatives, Part 6: A fundamental system of equations to describe ABC(3k,6ϕ) dynamics. A contribution to the elucidation of [2H]‐naphthopyran kinetics

“…In other words, there is always a (one or two photon) photochemical route predicted for the formation of species C from the initial closed form. If it is possible to draw the conclusion that the A → C direct photochemical reaction is negligible, which corroborates the experimental data corresponding to several unsubstituted and substituted derivatives of benzopyran 30,31, then parameter sets S b , S d , and S f may be eliminated from consideration (as ϕ BC ≈ 0) leaving three ( S a , S c , and S e ) mechanisms to account for the kinetics of compound 1 . It is worth noting that two among these sequences ( S a and S c ) represent a similar generic ABC(1 k ,5ϕ) mechanism (as ϕ AC ≈ 0) and can be seen as an example of the unidentifiability of the solution.…”

Synthesis of novel photochromic pyrans via palladium-mediated reactions

“…This spectral and temporal behaviour is already known from other naphtho- and benzopyrans as well as for spiropyrans [ 20 , 32 ]. The initial transients are assigned to the first excited singlet state [ 32 ].…”

“…The time constant for the formation of the open form (31 ps) is slower than the reaction dynamics recorded for other benzopyrans [ 20 , 32 ]. The slow reaction speed may be related to the cyano substituent at the 3-position in the benzopyran moiety (compare Scheme 2 ).…”

“…UV light-illumination of naphtho- and benzopyrans (closed forms), also referred to as chromenes, leads to the formation of interconverting photoisomers of the open merocyanine-type (quinoidal, zwitterionic and hybrid forms and their stereoisomers), depending upon the substitution pattern of the parent pyrans and the conditions employed ( Scheme 1 ). Typically the thermal reversion of the open forms is very fast [ 17 – 20 ].…”

Quantum-controlled color: chirp- and polarization-sensitive two-photon photochromism of spiropyrans in the solid phase

“…The photochromic reaction in spiropyran compounds proceeds [23] through C-O bond cleavage (the upper inset in Fig. 1) and relaxation from a transient state (state X in Fig.…”