Unusual UV (λexc = 303 nm) and visible (λexc = 574 nm) activated photochromism of an indeno-fused naphthopyran

Influence of (2,3,4,5,6-Pentamethyl/phenyl)phenyl Scaffold: Stereoelectronic Control of the Persistence of o-Quinonoid Reactive Intermediates of Photochromic Chromenes

“…As the TT isomer is populated only to a negligible/minor degree by a two-photon process, it may be considered as insignificant. Thus, the kinetic data in Table show that the values of rate constant k 1 , attributed to TC isomer, for all cases are significantly longer and compare well with those reported for the TC isomers derived from aryl-substituted chromenes or naphthopyrans in which the mesomeric effects decisively stabilize the o -quinonoid intermediates. ,− , Given that the mesomeric effects are not possible in all the intermediates of chromenes 1 Ch, 2 Ch, 4 Ch, and 5 Ch, we believe that intramolecular charge-transfer is likely to be the origin of the observed stabilization of the photogenerated o -quinonoid intermediates. Inspection of the absorption data and the decay rate constants ( k 1 ) in Table for the intermediates of 1 Ch, 2 Ch, 4 Ch, and 5 Ch reveals that the intermediates of 1 Ch and 2 Ch are slightly red-shifted and decay rather slowly relative to those of 4 Ch and 5 Ch.…”

“…As mentioned previously, the o -quinonoid intermediate of the parent chromene is very short-lived at room temperature . The strategies to render the o -quinonoid intermediates as rather longer-lived include benzoannulation, fluorene-annulation, arylation at 6- and 7-positions, etc. ,, It is indeed intriguing that the intermediates of 1 Ch, 2 Ch, 4 Ch, and 5 Ch exhibit considerably enhanced persistence given that the (pentaphenyl)phenyl/pentamethylpheny moieties are orthogonal to the chromene. In view of fast decay of the CC isomer and inaccessibility of the CT isomer (Scheme ) as mentioned previously, the rate constants k 1 and k 2 extracted from kinetic monitoring may be assigned to TC and TT, respectively.…”

The complex photochromic behaviour of 5,6-benzo(2H)dimethyl-chromene in 3-methylpentane solution

“…This suggests that the same nonactivated photochemical process governs the colour formation. The most acceptable general mechanism for the photoreactions of chromenes, which has been proposed by us 10,12, 16 and others, 17 assumes that quasi-planar cis and trans quinoidal species could potentially be formed in parallel reactions from the distorted precursor which is primarily formed from the starting chromene. The most important structural factor governing the distribution of photoproducts is the position of the benzo-ring condensation (7,8 or 5,6) in the chromene structure.…”

Photothermally Promoted Photoisomerization of Naphthopyran-Based Dyes to Achieve Sensitive Photodeformation under Sunlight

“…Although the photochromic process of these dye-PET films requires only a few seconds, it takes hours to fade back to the original colors (Figure a). According to the basic mechanism of decoloration process (Figure S30 in the Supporting Information), it is heavily dependent on the temperatures, and the higher the temperature, the faster the conversion of colored isomers to colorless isomers . The decreased absorbances at ∼600 nm (Figure S31 in the Supporting Information) were well-fitted by a monoexponential equation, and the decoloration rates of these colored films are similar to each other, and in the region of 1.88 × 10 –2 min –1 ∼ 2.83 × 10 –2 min –1 at room temperature (Table S4 in the Supporting Information).…”