Photonics and photochemical stability of aromatic molecules, family related in π-structure but different in planarity, rigidity and molecule symmetry

Intramolecular processes and fluorescence properties of 32 specially chosen aromatic molecules, different in degrees of planarity and rigidity, but family related in π-structure are experimentally and theoretically (using the PPP-method) studied at room temperature (293 K). The quantum yields of fluorescence γ, and decay times τf, of deaerated and non-deaerated cyclohexane solutions are measured. The oscillator strength fe, the fluorescence rate constants kf, the natural lifetimes τo T, and the intersystem crossing rate constants kST, are calculated. The investigations showed the following differences in the behaviour of the fluorescence parameters in transition from the non-planar molecule to the planar and more rigid-type: the value of the symmetry line wave-number υ00 (the frequency of the S0 → S1ππ* transition) and the Stokes shift ΔυST, decrease. The oscillator strength and fluorescence constant, normally decrease. The change in the quantum yield of the fluorescence depends upon the changes in the kf and kST values. Furthermore, the intersystem crossing rate constant generally decreases, sometimes very significantly. However, there are some interesting exceptions. For example, the kST value of the non-planar molecule of 9,10-diphenylanthracene is less than the kST value of the planar and very rigid molecule of anthracene. This important phenomenon is explained. The differences of the intramolecular processes of planar and non-planar molecules are discussed. The photochemical stability of planar and non-planar molecules is studied. The effect of planarity, rigidity and molecular symmetry upon laser properties is also traced. © 2008 Elsevier B.V. All rights reserved

Photonics and photochemical stability of aromatic molecules, family related in π-structure but different in planarity, rigidity and molecule symmetry

Intramolecular processes and fluorescence properties of 32 specially chosen aromatic molecules, different in degrees of planarity and rigidity, but family related in π-structure are experimentally and theoretically (using the PPP-method) studied at room temperature (293 K). The quantum yields of fluorescence γ, and decay times τf, of deaerated and non-deaerated cyclohexane solutions are measured. The oscillator strength fe, the fluorescence rate constants kf, the natural lifetimes τo T, and the intersystem crossing rate constants kST, are calculated. The investigations showed the following differences in the behaviour of the fluorescence parameters in transition from the non-planar molecule to the planar and more rigid-type: the value of the symmetry line wave-number υ00 (the frequency of the S0 → S1ππ* transition) and the Stokes shift ΔυST, decrease. The oscillator strength and fluorescence constant, normally decrease. The change in the quantum yield of the fluorescence depends upon the changes in the kf and kST values. Furthermore, the intersystem crossing rate constant generally decreases, sometimes very significantly. However, there are some interesting exceptions. For example, the kST value of the non-planar molecule of 9,10-diphenylanthracene is less than the kST value of the planar and very rigid molecule of anthracene. This important phenomenon is explained. The differences of the intramolecular processes of planar and non-planar molecules are discussed. The photochemical stability of planar and non-planar molecules is studied. The effect of planarity, rigidity and molecular symmetry upon laser properties is also traced. © 2008 Elsevier B.V. All rights reserved

A portable single-basin solar still with an external reflecting booster and an outside condenser

In this paper, a new design of a portable thermal-electrical solar still with an external reflecting booster and an outside condenser is proposed. The still minimises the loss of latent heat of condensation to the environment. The latent heat is accumulated in a condenser and can be used to preheat saline water for domestic purposes or to operate the still during night times. Preliminary results show that the efficiency of such still could be up to 77% if the preheated saline water is used for domestic purposes, and it could be up to 85% if preheated saline water is used to operate the still during night times and to recharge the still by the next batch of preheated water. © 2011 Elsevier B.V

Systematic investigation of the influence of methyl groups upon fluorescence parameters and the intersystem crossing rate constant of aromatic molecules

The absorption and fluorescence properties of 29 specially selected methyl substituted benzene, naphthalene, anthracene, biphenyl, fluorene and p-oligophenylenes compounds are studied experimentally (at 293 K) and quantum-chemically. The fluorescence quantum yield, γ, and decay times, τf, for deaerated and non-deaerated solutions were measured. The oscillator strength, fe, natural lifetime, τf 0 and fluorescence and intersystem crossing rate constants, kf and kST, respectively, are calculated for each compound. The orbital nature of the lowest excited singlet state, S1, is determined. The investigation shows that the introduction of methyl groups onto aromatic compounds may produce different effects. For example, the symmetry and hence kST and kf may change. As a result, γ will also change. Steric hindrance, caused by the CH3 group(s) will decrease kf while increasing kST. In cases where the introduction of the methyl group leaves the symmetry unchanged, there is a slight increase in kST but a slight decrease in kf. This effect is cumulative (more CH3 groups lead to a greater decrease in γ) and is attributable to the torsional vibrations of the methyl groups. Cases where introduction of CH3 group(s) causes the inversion of 1La and Tβ levels are observed and explained. Such inversion is accompanied by the increase in kf and sometimes, by the significant decrease in kST, which leads to a dramatic increase in the fluorescence quantum yield. Such changes improve laser properties or can convert a non-lasing compound to a lasing one. It is predicted that the CH3 group(s) can cause the inversion of 1La and 1La or Sπ π* 1 and Tn π* 1 levels, which can change the nature of fluorescence or can change a nonfluorescent compound to a fluorescent one. The trends observed may be used to change fluorescence properties of an aromatic compound in the necessary direction without changing its π-system. © 2009 Elsevier B.V. All rights reserved

A portable single-basin solar still with an external reflecting booster and an outside condenser

In this paper, a new design of a portable thermal-electrical solar still with an external reflecting booster and an outside condenser is proposed. The still minimises the loss of latent heat of condensation to the environment. The latent heat is accumulated in a condenser and can be used to preheat saline water for domestic purposes or to operate the still during night times. Preliminary results show that the efficiency of such still could be up to 77% if the preheated saline water is used for domestic purposes, and it could be up to 85% if preheated saline water is used to operate the still during night times and to recharge the still by the next batch of preheated water. © 2011 Elsevier B.V

Oscillator strengths of optical transitions of a cylindrical shell : Crossed static electric and magnetic fields

The single-electron eigenstates of a cylindrical shell are determined as functions of the applied crossed electric and magnetic fields in the effective-mass approximation. The system considered consists of donor charges taken to be uniformly distributed within an inner core of infinitely long length. The core is concentrically enveloped by a semiconducting material of finite thickness; which is essentially the host material. This configuration of the donor charges sets up a spatially varying electric field nonetheless with only the radial component. In addition, a uniform magnetic field is applied parallel to the axis of symmetry of the inner core. As is well known, the axial applied magnetic field lifts the double degeneracies of the electron’s subbands characterized by the same azimuthal quantum numbers which differ only in sign. The main effect of increasing the external electric field is to elevate the various energy subbands, more or less to the same extent, to higher values. Further, evaluations of the oscillator strengths of optical transitions of the cylindrical shell are carried out within the dipole approximation. The radiation field is taken to be that of circularly polarized light incident along the axis of the core. The oscillator strengths of optical transitions are found to increase with an increase of the applied magnetic field, particularly in the regime of small magnetic fields. In contrast, the oscillator strengths of these optical interactions become suppressed as the donor charge density is increased

Photochromism, anomalous multi-banded fluorescence and laser properties of some amino- and tosyl-amino derivatives of oxadiazole

The multi-banded fluorescence and laser properties of 11 new amino- and tosylamino derivatives of 2,5-di(phenyl)-1,3,4-oxadiazole and oxadiazole in various solvents at 293 K are reported. All the compounds investigated possess intra-molecular hydrogen quasi-bond (IHB) of 4.6-5.2 kcal mol-1 in the ground state. In the excited state they can undergo protolytic dissociation or intra-molecular photon-initiated transfer of proton and reveal anomalous fluorescence which cannot be explained within the framework of the Kasha and Kasha-Vavilov rules. Depending upon the excitation wavelength, solvent, concentration and pH of the medium, the compounds studied show a single, double, triple or even a four-banded fluorescence, which has not been reported earlier. The nature of multi-banded fluorescence is explained in terms of the possible photochromic processes in excited states. Quantum yields and decay times of the different fluorescence bands are reported. Anomalous dependence of quantum yield upon concentration of the solution is observed. Laser properties of the compounds studied are carefully tested. Laser action based on the fluorescence of the so-called bi-radical molecules is reported. Various possible arrangements of singlet and triplet levels of compounds investigated are discussed. © 2005 Elsevier B.V. All rights reserved

Systematic investigation of the influence of methyl groups upon fluorescence parameters and the intersystem crossing rate constant of aromatic molecules

The absorption and fluorescence properties of 29 specially selected methyl substituted benzene, naphthalene, anthracene, biphenyl, fluorene and p-oligophenylenes compounds are studied experimentally (at 293 K) and quantum-chemically. The fluorescence quantum yield, γ, and decay times, τf, for deaerated and non-deaerated solutions were measured. The oscillator strength, fe, natural lifetime, τf 0 and fluorescence and intersystem crossing rate constants, kf and kST, respectively, are calculated for each compound. The orbital nature of the lowest excited singlet state, S1, is determined. The investigation shows that the introduction of methyl groups onto aromatic compounds may produce different effects. For example, the symmetry and hence kST and kf may change. As a result, γ will also change. Steric hindrance, caused by the CH3 group(s) will decrease kf while increasing kST. In cases where the introduction of the methyl group leaves the symmetry unchanged, there is a slight increase in kST but a slight decrease in kf. This effect is cumulative (more CH3 groups lead to a greater decrease in γ) and is attributable to the torsional vibrations of the methyl groups. Cases where introduction of CH3 group(s) causes the inversion of 1La and Tβ levels are observed and explained. Such inversion is accompanied by the increase in kf and sometimes, by the significant decrease in kST, which leads to a dramatic increase in the fluorescence quantum yield. Such changes improve laser properties or can convert a non-lasing compound to a lasing one. It is predicted that the CH3 group(s) can cause the inversion of 1La and 1La or Sπ π* 1 and Tn π* 1 levels, which can change the nature of fluorescence or can change a nonfluorescent compound to a fluorescent one. The trends observed may be used to change fluorescence properties of an aromatic compound in the necessary direction without changing its π-system. © 2009 Elsevier B.V. All rights reserved

Photochromism, anomalous multi-banded fluorescence and laser properties of some amino- and tosyl-amino derivatives of oxadiazole

The multi-banded fluorescence and laser properties of 11 new amino- and tosylamino derivatives of 2,5-di(phenyl)-1,3,4-oxadiazole and oxadiazole in various solvents at 293 K are reported. All the compounds investigated possess intra-molecular hydrogen quasi-bond (IHB) of 4.6-5.2 kcal mol-1 in the ground state. In the excited state they can undergo protolytic dissociation or intra-molecular photon-initiated transfer of proton and reveal anomalous fluorescence which cannot be explained within the framework of the Kasha and Kasha-Vavilov rules. Depending upon the excitation wavelength, solvent, concentration and pH of the medium, the compounds studied show a single, double, triple or even a four-banded fluorescence, which has not been reported earlier. The nature of multi-banded fluorescence is explained in terms of the possible photochromic processes in excited states. Quantum yields and decay times of the different fluorescence bands are reported. Anomalous dependence of quantum yield upon concentration of the solution is observed. Laser properties of the compounds studied are carefully tested. Laser action based on the fluorescence of the so-called bi-radical molecules is reported. Various possible arrangements of singlet and triplet levels of compounds investigated are discussed. © 2005 Elsevier B.V. All rights reserved