Photoisomerization ofcis-1-(3-Methyl-2-naphthyl)-2-phenylethene in Glassy Methylcyclohexane at 77 K

Abstract

The cis-trans photoisomerizations of cis-1-(3-methyl-2-naphthyl)-2-phenylethene (c-3-MPE) was studied in methylcyclohexane (MCH) glass at 77 K. The fluorescence spectra of c- and t-3-MPE are excitation wavelength (λ(exc)) independent because the steric requirement of the methyl group restricts the conformational space of each isomer to a single conformer. Photocyclization, the dominant reaction pathway of c-3-MPE in solution, is entirely suppressed in MCH glass at 77 K. The only reaction on 313 nm irradiation of c-3-MPE in MCH glass is cis-trans isomerization. As the reaction progresses, the structureless fluorescence of c-3-MPE is replaced by the vibronically resolved fluorescence of the stable conformer of the trans isomer. The results are consistent with photoisomerization by the conventional one bond twist (OBT) pathway. Previously reported results on the photoisomerization of cis-1-(2-naphthyl)-2-(o-tolyl)ethene (c-NTE) are reinterpreted. Calculated geometries and energy differences for c- and t-3-MPE and c- and t-NTE [DFT using B3LYP/6-311+G(d,p)] are consistent with the interpretation of the experimental results.

Lumisterol to Tachysterol Photoisomerization in EPA Glass at 77 K. A Comparative Study

“…Results for Pre are summarized in Table . The shortcomings of DFT B3LYP calculations to accurately predict relative hydrocarbon energy differences have been highlighted in several recent publications. , In our experience, very good agreement between experimental results and DFT B3LYP theoretical predictions was realized for conformer and isomer energetics of a simple butadiene, diphenylpolyenes, − and 1,2-diarylethenes ,, in their S 0 and T 1 states. The calculations predict a plethora of Pre and Tachy conformers in close energetic proximity.…”

Photoisomerization of cis‐1,2‐di(1‐Methyl‐2‐naphthyl)ethene at 77 K in Glassy Media

“…Formation of an unstable trans conformer starting from the o ‐tolyl analog of c ‐NPE ( c ‐NTE, Scheme , in EPA glass at 77 K was thought to confirm the benzylic HT pathway . On the basis of the known t ‐NPE A and t ‐NPE B absorption spectra , we pointed out that the correct assignment of the thermal relaxation of the photoproduct of c ‐NTE in EPA glass at 77 K is t ‐NTE A → t ‐NTE B (Scheme , right side). Therefore, depending on the correct structural assignment to the c ‐NTE conformer that exists in EPA glass, either the HT or the OBT mechanism will account for the results.…”

“…We showed that at 77 K in glassy MCH the photoisomerizations of cis ‐1‐(2‐naphthyl)‐2‐phenylethene ( c ‐NPE, Scheme , that exists mainly as the B conformer and cis ‐1‐(3‐methyl‐2‐naphthyl)‐2‐phenylethene ( c ‐3‐MPE) that should exist as the A conformer (Scheme , bottom left, proceed as shown by the OBT labeled pathways c ‐NPE B → t ‐NPE B and c ‐3‐MPE A → t ‐MPE A in Scheme . However, our conclusion that no HT is involved in those reactions was dismissed because HT photoisomerization about the benzylic CH would lead to the same result .…”

“…We showed that at 77 K in glassy MCH the photoisomerizations of cis-1-(2-naphthyl)-2-phenylethene (c-NPE, Scheme 1, R = R = H) that exists mainly as the B conformer (18) and cis-1-(3-methyl-2-naphthyl)-2-phenylethene (c-3-MPE) that should exist as the A conformer (19) (Scheme 1, bottom left, R = CH 3 , R = H, c-3-MPE A ) proceed as shown by the OBT labeled pathways c-NPE B ? t-NPE B and c-3-MPE A ?…”

Donor-Acceptor Conjugated Linear Polyenes: A Study of Excited State Intramolecular Charge Transfer, Photoisomerization and Fluorescence Probe Properties

“…The photoisomerization in linear polyenes is highly regioselective and is much influenced by substitutent, polarity of the medium [28][29][30][31][32][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] and dipolar nature of the excited state [74][75][76][77][78]. Various mechanistic models have been proposed to understand the photoisomerization process of retinyl and related polyenes.…”