Vibronic Effects in Photochemistry—Competition between Internal Conversion and Photochemistry

Becker, Ralph S.; Dolan, E.; Balke, David E.

doi:10.1063/1.1670783

Cited by 91 publications

(62 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…It was previously shown that certain naphthopyrans exhibit decreased fluorescence and/or increased photochemistry when upper vibrational levels within S 1 are excited, [18][19][20][21][22] whereas for molecules not showing photochemistry the fluorescence quantum yield was independent of the exciting wavelength. [18] It has also been demonstrated, by a kinetic/thermodynamic approach, that the ring-opening reaction is an extremely fast process and therefore can compete with vibrational relaxation.…”

Section: Wavelength Dependence Of Fluorescence and Photochemistrymentioning

confidence: 98%

Photochromic, Thermochromic, and Fluorescent Spirooxazines and Naphthopyrans: A Spectrokinetic and Thermodynamic Study

et al. 2008

View full text Add to dashboard Cite

The photochromic and thermochromic behavior of four commercially available Reversacol dyes are presented. The compounds studied belong to the class of spirooxazines and naphthopyrans, which are typically thermoreversible photochromic molecules. On stimulation with UV light, these compounds become colored and exhibit spectra which extend over the whole visible region. Increasing the temperature causes spontaneous coloration (thermochromism). Herein, absorption and fluorescence spectra, molar absorption coefficients of the colorless and colored forms, fluorescence and photochemical quantum yields, and kinetic parameters of thermal bleaching (rate constant, frequency factor, and activation energy) are determined in acetonitrile solution. The thermal ground-state reaction is exhaustively described in terms of thermodynamic parameters (equilibrium constant, free energy, enthalpy, and entropy). Temperature effects on photochemical and thermal colorabilities are evaluated. The results indicate that the two spirooxazines are good photochromes below room temperature, whereas they are efficient thermochromic compounds above room temperature. Naphthopyrans are better photochromes but worse thermochromic compounds than spirooxazines.

show abstract

Section: Wavelength Dependence Of Fluorescence and Photochemistrymentioning

confidence: 98%

Photochromic, Thermochromic, and Fluorescent Spirooxazines and Naphthopyrans: A Spectrokinetic and Thermodynamic Study

et al. 2008

View full text Add to dashboard Cite

show abstract

“…This shows that some of the energy delivered by the photon in excess of that needed for a purely electronic excitation (0-0 transition) is not lost as heat until after it has been utilized for motion across the small barrier separating the minimum at the initial geometry from the product side. Such extremely rapid photochemical processes, capable of competing with thermal deactivation in condensed media, have been described previously (Becker et a/., 1969), but this appears to be the first case in which one can be sure that the whole process involves only the singlet manifold (the molecule is still in the singlet state after the escape since it fluoresces at the end). In the previous reported cases, involvement of intersystem crossing was unlikely but hard to exclude with certainty.…”

Section: (B) Electrocyclic Ring Opening In Dewar Aromaticsmentioning

confidence: 99%

The Role of Biradicaloid Geometries in Organic Photochemistry

Michl

1977

Photochem & Photobiology

View full text Add to dashboard Cite

Abstract-Excited molecules tend to return to the ground state at biradicaloid geometries, i.e. those for which the simple MO description yields two non-bonding orbitals occupied by only two electrons in the ground state. The nature of electronic states at these geometries and the consequences for the course of photochemical reactions are summarized, using the cases of Hz and H4 as simple models. Several aspects of classification schemes for photochemical reactions are discussed.Detailed mechanisms of photocycloaddition, of adiabatic photochemical rearrangement of Dewar aromatics, and of luminol chemiluminescence are considered as examples.

show abstract

“…[1][2][3] Chromenes, a class of photochromic compounds, have been studied in their photochromic properties in the pioneering work by Becker et al more than 30 years ago. [4][5][6][7][8][9][10][11] Naphthopyran is a chromene derivative (benzochromene) and can be divided into three isomers, 3H-naphtho [2,1-b]pyrans, 2H-naphtho [1,2-b]pyrans, and 2H-naphtho [2,3-b]pyrans (Scheme 1). The photochemistry and photophysics of 3H-naphtho [2,1-b]pyrans were extensively studied.…”

Section: Introductionmentioning

confidence: 99%

Photochromism of 2H-Naphtho[1,2-b]pyrans: A Spectroscopic Investigation

2002

View full text Add to dashboard Cite

The photophysical and photochromic properties of 2,2-diphenyl-2H-naphtho [1,2-b]pyran and substituted derivatives were investigated by steady state and time-resolved optical absorption and emission spectroscopy in solution at room temperature and in a frozen matrix at 77 K. Fluorescence quantum yields, fluorescence lifetimes, and singlet energies depend strongly on the substitution patterns. Photoexcitation of the naphthopyrans (A) leads to efficient ring opening to produce the merocyanines (B) and (C). The optical absorption of the merocyanines can be tuned by the substituents and can cover most of the visible spectrum (400-700 nm). The decoloration kinetics of the open forms (merocyanines) B and C to produce naphthopyrans (A) depends strongly on the substituents. The ring closure rate constants (k BfA ) range from 0.0009 to 0.04 s -1 . IntroductionIn the past few years, photochromic dyes, which show reversible photoisomerization, have attracted considerable attention because of their implications in a great number of practical applications including data storage, optical filters, displays, sensor protection, waveguides, and ophthalmic plastic lenses. 1-3 Chromenes, a class of photochromic compounds, have been studied in their photochromic properties in the pioneering work by Becker et al. more than 30 years ago. [4][5][6][7][8][9][10][11] Naphthopyran is a chromene derivative (benzochromene) and can be divided into three isomers, 3H-naphtho[2,1-b]pyrans, 2H-naphtho[1,2-b]pyrans, and 2H-naphtho[2,3-b]pyrans (Scheme 1). The photochemistry and photophysics of 3H-naphtho[2,1-b]pyrans were extensively studied. 9,10,[12][13][14][15][16][17][18] Although, 2H-naphtho[1,2-b]pyrans are commercially used in plastic ophthalmic lenses, 19 systematic studies of the photophysics and photochemistry are surprisingly rare. 8,20,21 Most studies concentrated on synthetic aspects. 15,17,22,23 Therefore, we investigated in detail the photophysics and photochemistry of 2,2-diphenyl-2H-naphtho[1,2-b]pyran, 1(A), and four of its derivatives, 2(A)-5(A), (Scheme 1). The derivatives 2(A)-5(A) were chosen to study influences of substituents on the properties.Ottavi et al. showed that irradiation with UV light of 3,3-diphenyl-3H-naphtho[2,1-b]pyran produces two colored forms of ring opening products (cis-trans and trans-trans). 12 Applying this reaction mechanism to 1(A) leads to Scheme 2 in which A is the (uncolored) closed form (pyran form) and B (cis-trans) and C (trans-trans) are open (colored) forms (merocyanine forms). For this investigation, the photophysical properties of the closed form (A) and the open forms (B and C) were determined separately, and afterward, the ring closure kinetics (B and C to A) were investigated. Experimental SectionThe naphthopyrans 1(A)-5(A) (PPG Industries, Inc.) were recrystallized from ethanol. Acetonitrile, ethanol, and methylcyclohexane (Aldrich, spectroscopic grade) were used as received.The UV-vis spectra were recorded on a HP 8452A diode array spectrophotometer using quartz cells with path lengths...

show abstract

Vibronic Effects in Photochemistry—Competition between Internal Conversion and Photochemistry

Cited by 91 publications

References 14 publications

Photochromic, Thermochromic, and Fluorescent Spirooxazines and Naphthopyrans: A Spectrokinetic and Thermodynamic Study

Photochromic, Thermochromic, and Fluorescent Spirooxazines and Naphthopyrans: A Spectrokinetic and Thermodynamic Study

The Role of Biradicaloid Geometries in Organic Photochemistry

Photochromism of 2H-Naphtho[1,2-b]pyrans: A Spectroscopic Investigation

Contact Info

Product

Resources

About