Joel M. Kauffman

Computational methods as an aid in the design of fluorophores with predictable absorption and emission wavelengths

Abstract Semiempirical computational methods (AM1 for geometries, ZINDO for electronic transition energies) were used to calculate the absorption and fluorescence spectra of a series of oligophenylenes, their heteroaromatic substituted derivatives, and aryl substituted open-chain and bridged polyenes. The calculations were calibrated on a series of 61 (for absorption) and 42 (for fluorescence) compounds and are shown to reproduce experimental data with an accuracy of −1 . Based on these results, calculations on possible synthetic targets for compounds to be used as scintillating fluors in high-energy particle detection were performed, whereby absorption and emission wavelengths were predicted for 15 and 34 compounds, respectively.

Electronic absorption and emission spectral data and fluorescence quantum yields of bridgedp-oligophenylenes, bi- to deciphenyls, and related furans and carbazoles

Absorption and fluorescence emission spectral data, as well as fluorescence quantum yields (Φf), were determined for 41p-oligophenylene compounds containing 2–6, 8, and 10 benzene rings. Of 29 compounds containing carbon-bridged rings (fluorenes), 28 were dialkylated on each bridge for improved solubility and photostability. Absorption maxima for oligophenylenes were observed at wavelengths as long as 366 nm, emission maxima to 437 nm, and molar extinction coefficients (ɛ) as large as 153,000 L/mol-cm; all three exceeded predicted maximum values for the corresponding unbridged oligophenylenes. The substitution of furan for benzene or carbazole for a fluorene (two examples each) bathochromically shifted absorption and emission maxima. Dialkylated carbon bridges bathochromically shifted absorption and emission maxima, and lowered Φf in biphenyl and in one terphenyl analogue, but appeared to cause no diminution of Φf in higher oligophenylenes. Bis(2-methoxyethyl) substitution on the bridges, incorporated to provide solubility in polar solvents, lowered Φf in all examples. Tertiary alkyl substituents on terminal rings bathochromically shifted the absorption and emission maxima and generally increased Φf. The “loose bolt” effect, which lowers Φf in mononuclear substituted benzenes, may operate in 9,9-dialkylfluorenes, but not in 2,7-di-t-butylfluorene or in higher oligophenylenes. Cyclic ether and methoxy substituents as auxofluors on terminal rings generally bathochromically shifted absorption and emission maxima and increased ɛ and Φf. Cyano substituents bathochromically shifted absorption and emission maxima, and increased ɛ, but lowered Φf slightly.

Excited state proton transfer in jet-cooled 2,5-di-(2-benzoxazolyl)phenol

Abstract The molecule 2,5-di-(2-benzoxazolyl)phenol (DBP) has been studied by laser spectroscopy in a supersonic free jet. In the jet the fluorescence with a Stokes shift of 7000 cm −1 arises exclusively from the proton-transferred species. The fluorescence excitation spectrum of DBP exhibits the broad fluorescence background underlying some weak, sharp features. The first prominent band has been observed at 27830 cm −1 , but from 250 cm −1 above the origin the spectrum becomes congested and broad. OH→OD substitution of DBP produces a blue shift of 103 cm −1 . For the deuterated sample (DBP-d 1 ) resolved line structure in the fluorescence excitation spectrum has been observed up to an excess energy of 400 cm −1 . To identify spectral features corresponding to deuterated DBP and other species double-resonance depletion spectroscopy has been applied. From analysis of the width of the vibronic bands of DBP-d 1 , we estimated an upper limit of the excited state deuteron transfer rate constant, k DT =1.7×10 12 s −1 .

Bridged quaterphenyls as flashlamp-pumpable laser dyes

Partial bridging of the o,o′ positions of the aromatic rings in quaterphenyl gave superior flashlamp-pumpable laser dyes. Alkyl-substituted carbon bridges gave superior dyes to those containing oxygen or alkyl-substituted nitrogen or silicon bridges. Dyes lasing in the 365–390 nm region with improved energy output, lifetime and solubility were discovered.

Laser dye structures and synonyms

Laser dyes are organic chemicals whose systematic names are lengthy and confusing. Other names-some jargon, some trade-have come into everyday use, but there is no consistency, and sometimes research workers will have dyes from different suppliers that are identical in structure although different in name. This paper tabulates laser dyes by a characteristic identification number.

SYNTHESIS OF JULOLIDINE DERIVATIVES

(2001). SYNTHESIS OF JULOLIDINE DERIVATIVES. Organic Preparations and Procedures International: Vol. 33, No. 6, pp. 603-613.

Cyclic Ether Auxofluors on Oligophenylene Laser Dyes

Laser dyes with terphenyl and quaterphenyl as the fluorophors and with acyclic ether auxofluors were improved when the ether groups were made cyclic. Dyes containing cyclic ethers in 5- and 6-membered rings were observed to lase in the 360–400 nm region with better lifetime and/or solubility than their acyclic analogs. In one case the laser output wavelength of a quaterphenyl fitted with cyclic ether auxofluors was red-shifted enough to match the wavelength of a sexiphenyl without auxofluors.

Effect of Various Anions and Zwitterions on the Lasing Properties of a Photostable Cationic Laser Dye

An unusually photostable cationic laser dye first prepared by quaternization of the free base 4PyMPO (Figure 1) with methyl p-toluenesulfonate unexpectedly had, when flashlamp pumped in methanol, half the energy output of four other N-methyl quaternary salts: the methanesulfonate, the trifluoromethanesulfonate, the perchlorate, and the tetrafluoroborate. When four homologous zwitterions (Figure 2) prepared from 4PyMPO were tested in methanol, the output energies ranged from 1.4 to 2.5 times that of the p-toluenesulfonate, and up to 1.3 times that of the salt with the highest output. When flashlamp pumped in water, the zwitterions showed 1.5 to 2.0 times the output energy of the p-toluenesulfonate in water. Many of the dyes displayed laser output curves that were split in the middle, so that lasing energy appeared on either side of a dark valley. Among the zwitterions, a regular shifting from red to blue was observed as the carbon chain length was increased.

New quench-resistant fluors for liquid scintillation counting

Abstract Several new fluors of the oligophenylene type were synthesized and compared with the most commonly used fluors in liquid scintillation cocktails. These new fluors, which are diaryl derivatives of fluorene or 2,2′-bifluorene, provided the most efficient fluor systems studied to date, particularly when chemically quenched in a non-aqueous system, or quenched with water in an emulsifier-containing system.

Synthesis of Bridged Oligophenylenes from Fluorene. Part 1. Ter- and Quater-phenyls

Alkylation and halogenation of fluorene give halogenated 9,9-dialkylfluorenes, which are converted by Pd-catalysed coupling with aryl Grignard reagents into a series of ter- and quater-phenyls exhibiting strongly efficient fluorescence, useful solubility and photochemical stability.