Two free base porphyrins, 5,10-bis(4-aminophenyl)-15,20-diphenylporphyrin (cis-DATPP), 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin (trans-DATPP), and their zinc metalated analogues (cis-ZnDATPP and trans-ZnDATPP) were synthesized. A series of their corresponding polyimides were obtained by the condensed polymerization of the respective monomeric isomer DATPP with a 1:1 ratio of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB) and 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA). The inclusion of PFMB and 6FDA into the polymeric backbone causes the polymers to be moderately to highly soluble in organic polar solvents. The molar content of the respective DATPP monomer varied between 5 and 30%. All compounds were structurally characterized by 1H NMR and ATR-IR spectroscopy and the porphyrin content in the polyimides was determined by UV–Visible absorption spectroscopy. Photophysical properties consisted of measuring both the UV–Visible (ground state) absorption and fluorescence (excited state) spectra, fluorescence quantum yields (Φf), and fluorescence lifetimes (τf) in dichloromethane and N,N-dimethylacetamide. Fluorescence quenching was also measured and observed by the Stern-Volmer relationship, using 9,10-anthraquinone (AQ) as the quencher molecule. Both the bimolecular rate constant of fluorescence quenching (kq) and the Stern-Volmer constant (KQ) were calculated from this relationship. Furthermore, deviations from linearity depicted in the Stern-Volmer plots for TPP and ZnTPP at higher concentrations of AQ were also measured as a means of examining and explaining the simultaneous occurrence of dynamic (collisional) quenching and static quenching in the mechanisms of fluorescence quenching. It was found in this work that the significantly larger values in the static quenching constant (KS) than in the dynamic quenching constant (KD) are indicative that static quenching and ground state complex formation between the fluorophore and quencher is the dominant mechanism of fluorescence quenching of these systems at higher quencher concentrations.

A series of alkylamino substituted 2-arylidene and 2,5-diarylidene cyclopentanone compounds were synthesized. Spectroscopic and photophysical properties of these compounds have been measured in a variety of solvents. Absorption and fluorescence maxima have been correlated with the Empirical Scale of Solvent Polarity (ET(30)). Theoretical TD-DFT spectral calculations and Lippert–Mataga analysis support the internal charge transfer (ICT) nature of the S0 → S1 excitation for these compounds, with higher degrees of ICT depicted for the alkylamino substituted 2,5-diarylidene cyclopentanones. Photophysical properties consisted of measuring the fluorescence quantum yields (Φf) and lifetimes (τf) in a variety of solvents. Radiative and nonradiative decay constants have been determined from the Φf and τf data. Variation with solvent in the nonradiative rate of decay is interpreted in terms of a competition between internal conversion and intersystem crossing. Lastly, two compounds presented have been shown to undergo excited state protonation in glacial acetic acid.

Photochemical studies of (2E,5E)-2,5-bis(4-dimethylaminobenzylidene)-cyclopentanone (I) have been carried out. Compound I has been shown to sensitize the production of singlet oxygen (1O2) in deuterated toluene (C7D8), chloroform (CDCl3), and methanol (CD3OD). Tetramethylethylene (TME) was used as the indicator for 1O2 production. Photobleaching of solutions of the dye was observed, which led to an investigation of the chemical reactivity of I with 1O2. Based on 1H NMR, UV–Visible absorption spectroscopy, and HPLC/MS experimental data, it is proposed that the self-sensitized photooxidation of I with 1O2 yields 4-dimethylaminobenzaldehyde and (E)-3-(4-dimethylaminobenzylidene)-1,2-cyclopentadione as products. Photooxidation of I was not detected in CH3OH but was found in CD3OD. The absence of photooxidation in CH3OH is attributed to the short lifetime of singlet oxygen in this solvent (τΔ = 9.5 μs), compared to its lifetime in CD3OD (τΔ = 270 μs). UV–Visible absorption spectra of irradiated solutions of I in deoxygenated solvents demonstrate that (E,E) → (E,Z) photoisomerization of the dye takes place under these conditions.

Retinal prostheses promise to be a viable therapy for many forms of blindness. Direct stimulation of neurons using an organic light-sensitive, self-assembled monolayer surface offers a simple alternative to conventional semiconductor technology. For this purpose we have derivatized an indium tin oxide (ITO) substrate with the photosensitive dye, NK5962, using 3-(aminopropyl)trimethoxysilane (APTMS) as cross-linker. The surface was characterized through contact angle goniometry, electrochemical impedance spectroscopy, grazing angle infrared and ultraviolet–visible spectrophotometry. NG108-15 neurons were grown on the ITO-APTMS-NK5962 surface and neural responses from electrical stimulation vs. photostimulation through the ITO-APTMS-NK5962 surface were measured using patch clamp electrophysiology. Under these conditions, photostimulation of depolarized cells caused an approximate 2-fold increase in voltage-gated sodium (Na+) current amplitude at a membrane potential of −30 mV. Our results demonstrate the feasibility of stimulating neurons, grown on light-sensitive surfaces, with light impulses, which ultimately may facilitate the fabrication of a simple, passive retinal prosthetic.

Tetraphenylporphyrin (H2TPP), covalently linked to four 2-pyridone moieties was synthesized (II) and studied. This composite molecule, in combination with light and ground state oxygen, has the ability to generate, trap, store, and release singlet oxygen. The process can be operated reversibly without detectable decomposition or side reactions using light with wavelength greater than 500 nm. Oxidation of the target molecule, 2-chloroethyl ethyl sulfide (CEES), by singlet oxygen released from the endoperoxide of the porphyrin-2-pyridone molecule (I) is demonstrated. Spectroscopic and kinetic data do not reveal evidence of perturbation between the porphyrin and pyridone ring systems of II. The decomposition kinetics for the endoperoxide adduct I are first order with activation parameters Delta H double dagger = 26.7 (kcal/mol) and Delta G double dagger = 24.0 (kcal/mol). Experimental and computational studies of unattached N-benzyl-2-pyridone peroxide are reported and compared to the experimental data for I. (C) 2013 Elsevier B.V. All rights reserved.

Spectroscopic and photophysical properties have been measured in a variety of solvents for (2E,5E)-2-(p-cyanobenzylidene)-5-(p-dimethylaminobenzylidene)-cyclopentanone (I), an asymmetrically substituted 2,5-diarylidene-cyclopentanone known to have potential for applications utilizing two-photon absorption (TPA). Compound I was synthesized by a simple procedure utilizing DIMCARB catalyst. Absorption and fluorescence maxima have been correlated with the ET(30) solvent polarity scale. Theoretical TD-DFT calculations and Lippert–Mataga analysis demonstrate the internal charge transfer (ICT) nature of the S0→S1 excitation. Radiative and nonradiative decay constants have been determined from fluorescence quantum yields and lifetimes. Substantial variation with solvent in the rate of nonradiative decay is interpreted in terms of a competition between internal conversion and intersystem crossing.

Geometry optimization calculations at the B3LYP/6-311+G(d,p) level have been carried out for fulvene (FU) diphenylfulvene (DPFU), diphenylmethylenefluorene (DPMF), and 9-[pp′-bis(dimethylamino)diphenylmethylene]fluorene (DAMF). The phenyl torsion angles for DPFU, DPMF, and DAMF are predicted to be 46°, 56°, and 49°, respectively. Agreement between experimental NMR data and computed magnetic properties support the prediction that the phenyl twist angle of DAMF is less than that of DPMF. The optimized ground state geometries were used as input for TD-DFT calculations of the electronic spectra of the fulvenic compounds. Agreement between the experimental spectral data and theoretical results is good. The calculations indicate that the S0→S1 is primarily HOMO→LUMO for FU, DPFU, and DAMF and HOMO−1→LUMO for DPMF. Analysis of the nodal properties of the molecular orbitals shows that the HOMO of FU correlates with the HOMO of DPFU, HOMO−1 of DPMF, and HOMO−2 of DAMF. The LUMO of the compounds correlate with each other. Thus the lowest energy electronic transition is predicted to be B(B2)←A(A1) under C2(C2V) symmetry for FU, DPFU and DPMF. Whereas, S0→S1 is predicted to be A←A under C2 for DAMF. Assignments for other transitions appearing in the electron spectra are discussed.

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Chemischer InformationsdienstVolume 13, Issue 33 Physical Organic Chemistry ChemInform Abstract: ORIGIN OF THE UNUSUAL TRIPLET-STATE PROPERTIES OF XANTHONES R. E. CONNORS, R. E. CONNORSSearch for more papers by this authorW. R. CHRISTIAN, W. R. CHRISTIANSearch for more papers by this author R. E. CONNORS, R. E. CONNORSSearch for more papers by this authorW. R. CHRISTIAN, W. R. CHRISTIANSearch for more papers by this author First published: August 17, 1982 https://doi.org/10.1002/chin.198233050AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue33August 17, 1982 RelatedInformation

The phosphorescence spectrum of xanthone embedded in a polycrystalline matrix of n -hexane has been measured at 77 and 4.2 K. Dramatic differences in spectral features and triplet lifetime are evident at these two temperatures. The emitting species at 4.2 K is assigned as predominantly 3 (ππ*) in character; whereas, the phosphorescence state observed at 77 K is clearly 3 (nπ*).

Chemischer InformationsdienstVolume 7, Issue 36 Physical Organic Chemistry ChemInform Abstract: THE TRIPLET STATE OF CHLOROPHYLLS RICHARD H. CLARKE, RICHARD H. CLARKESearch for more papers by this authorROBERT E. CONNORS, ROBERT E. CONNORSSearch for more papers by this authorTJEERD J. SCHAAFSMA, TJEERD J. SCHAAFSMASearch for more papers by this authorJOOP F. KLEIBEUKER, JOOP F. KLEIBEUKERSearch for more papers by this authorROELOF J. PLATENKAMP, ROELOF J. PLATENKAMPSearch for more papers by this author RICHARD H. CLARKE, RICHARD H. CLARKESearch for more papers by this authorROBERT E. CONNORS, ROBERT E. CONNORSSearch for more papers by this authorTJEERD J. SCHAAFSMA, TJEERD J. SCHAAFSMASearch for more papers by this authorJOOP F. KLEIBEUKER, JOOP F. KLEIBEUKERSearch for more papers by this authorROELOF J. PLATENKAMP, ROELOF J. PLATENKAMPSearch for more papers by this author First published: September 7, 1976 https://doi.org/10.1002/chin.197636037AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue36September 7, 1976 RelatedInformation

The phosphorescent properties of closed shell metal chelates have been studied in EPA at 77°K. The compounds investigated include the acetylacetonates of magnesium and Group III-A metal ions (Al, Ga, In) as well as the trifluoroacetylacetonate and hexafluoroacetylacetonate chelates of aluminum. The results indicate that although the metal center does not greatly affect the position or vibronic structure of the acetylacetonate luminescence it is important in both intersystem crossing and radiative coupling to the ground state in these systems. It is also concluded that there is little or no interaction between the ligand rings in the emitting triplet state. Altering the electron distribution in the ligand ring by successively replacing the −CH3 groups with −CF3 groups results in a red shift in the location of the emission and a marked alteration in the vibronic envelope. The luminescence of single crystals of aluminum, indium and gallium acetylacetonate has also been investigated. All three crystals exhibit a broad, short-lived emission which is assigned as fluorescence from an excimer-like configuration.