Free-jet fluorescence excitation spectrum of t r a n s, t r a n s-1,3,5,7-octatetraene

Abstract

The fluorescence excitation spectrum from 2980 to 2650 Å of trans, trans-1,3,5,7-octatetraene in a free jet has been measured monitoring emission in the region 3250 to 3500 Å. The vibronic bands of the 1 1Bu←1 1Ag (S2←S0) transition of octatetraene narrow significantly in a seeded free jet of ∼8 ppm octatetraene in helium (FWHM∼200 cm−1 for the room temperature static gas; FWHM∼35 cm−1 in the jet). Although absolute intensities of the vibronic bands are not determined, there is significant intensity in the origin, and the vibronic development involves only a few modes. Estimated translational, rotational, and vibrational temperatures of ∼1,<45, and <170 K, respectively, were achieved in the expansion. The major source of the observed linewidth is attributed to coupling of the 1 1Bu state to the lower 1Ag states.

Time-dependent N-electron valence perturbation theory with matrix product state reference wavefunctions for large active spaces and basis sets: Applications to the chromium dimer and all-trans polyenes

“…66,67 The electronic spectra of all-trans polyenes have been the subject of many experimental and computational studies. 39,[67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85] Of particular interest are the excitation energies and ordering of the low-lying singlet electronic states. While the symmetry of the singlet ground state is known to always be A − g , the experimental and theoretical characterization of the low-lying singlet excited states has been very challenging.…”

One- and two-photon fluorescence excitation spectra of the 2 1A g states of linear tetraenes in free jet expansions

“…The fluorescence excitation spectrum of the S 2 ←S 0 transition of octatetraene also was obtained in a supersonic jet. 30 However, until recently the weak, symmetry-forbidden S 1 ↔S 0 transitions of linear polyenes had not been studied in the gas phase, in large part because of earlier reports of vanishingly small S 1 state fluorescence yields under isolated conditions. 5,[31][32][33] Two developments have opened the study of the S 1 states of polyenes in molecular beams.…”

Free jet excitation and emission spectra of diphenylbutadiene

“…Emission spectra and decay times for the 1Ag state were measured at a number of different excitation energies. These data clarify the ordering of excited singlet states and the photophysical behavior of diphenylbutadiene.The connection between electronic structure and photochemical behavior in the linear polyenes is the focus of a number of spectroscopic and theoretical investigations (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). Particularly for the shorter polyenes, the photophysics of these molecules is dramatically affected by the close proximity of the two lowexcited singlet states (21Ag and 11BJ).…”

“…In fact there is evidence that the separation and even the ordering of these states is a strong function of effective conjugation length and molecular environment (8,12,(15)(16)(17). While high-resolution spectroscopy in condensed and gas phases has greatly increased our insight into the photochemical behavior of polyenes, in particular octatetraene (8,9), less is known about the low-lying singlet states of hexatriene and butadiene. This is primarily because of the lack of detectable fluorescence (8), which is not a problem for the a,w-diphenylpolyenes.…”

“…The layout of our free jet apparatus is nearly the same as that described previously (9). The major difference is that now emission from the intersection of the jet and the frequencydoubled N2 laser-pumped dye laser beam is collected inside the chamber by an fl/ spherical mirror and focused at 8:1 magnification onto the entrance slit of a 1-m monochromator.…”