Synthesis and Nonlinear Optical, Photophysical, and Electrochemical Properties of Subphthalocyanines

Abstract

Novel boron(III) subphthalocyanines (SubPcs) soluble in organic solvents containing a variety of donor and acceptor substituent groups have been synthesized by boron trihalide-induced cyclotrimerization of adequately substituted derivatives of phthalonitrile in 1-chloronaphthalene. The choice of the substituents on the 1,2-dicyanobenzene derivatives has been made taking into account the high reactivity of the Lewis acid BCl3 toward many functional groups. Considering this limitation, we set out to synthesize phthalodinitriles equipped with iodo, nitro, alkyl- or arylthio, alkyl- or arylsulfonyl groups that are sufficiently stable under the required reaction conditions and also provide an easily accessible set of acceptor/donor substituents. The quadratic and cubic hyperpolarizabilities of these compounds as well as their linear optical and electrochemical properties have been measured by several techniques, including EFISH (at two wavelengths), HRS, and THG, steady-state and time-resolved absorption and fluorescence, laser-induced optoacoustic calorimetry, time-resolved near-infrared emission spectroscopy, and cyclic voltammetry. βHRS has been measured at 1.46 μm, where the contamination from the multiphoton-induced fluorescence can be ruled out. βHRS reachs high values that markedly depend on substitution. It shows a clear enhancement with the acceptor character of the substituents, the highest values being obtained for the compounds bearing the strongest acceptor groups. They are comparable or even superior to many efficient second-order compounds. A main outcome of these results is that an adequate choice of the substituents offers a promising route for optimization of the quadratic response of the SubPcs. This kind of compounds is less prone to aggregation than their expanded analogues, the phthalocyanines, fluoresces with quantum yields ca. 0.25, lower than those typical for phthalocyanines, and has larger triplet quantum yields. The triplet-state lifetime is in the 100-μs time range, long enough for efficient oxygen quenching. Indeed, subphthalocyanines sensitize singlet molecular oxygen, O2(1Δg), with quantum yields ranging from 0.23 to 0.75. The ground-state oxidation potentials are similar to those of phthalocyanines, while the reduction potentials are clearly more negative; i.e., they are more difficult to reduce. In contrast, electronically excited subphthalocyanines are more easily oxidized than the corresponding phthalocyanines by ca. 500 mV which results in lower photostability, especially in polar solvents.

The axial coordination in subphthalocyanines: Geometrical and electronic aspects

“…In spite of the indicated differences, the homogeneity of the orbital energy distribution in the studied compounds must be emphasized. This result is in perfect correspondence with the observed facts that the first half-wave potentials for electrochemical oxidative processes [13,31] as well as the positions of the B and Q bands in the UV-vis electronic spectra [19,31,32] of the selected SubPcs differ very little. The former of these experimental magnitudes depends on the HOMO's position whereas the energies of the Q and B electronic transitions are associated with the relative energetic differences among the two highest occupied and two lowest unoccupied molecular orbitals [15][16][17].…”

“…The subphthalocyanine (chlorosubphthalocyaninato boron(III)) (SubPc) has also proved to be of synthetic interest in its ring expansion reaction which is an attractive alternative method for synthesizing unsymmetrical phthalocyanines [6][7][8][9][10][11][12][13].…”

Dithienylcyclopentene-functionalised subphthalocyaninatoboron complexes: Photochromism, luminescence modulation and formation of self-assembled monolayers on gold

“…the photochromic dithienylcyclopentene moiety of the type 2 H and the SubPc-based headgroup, which is a strong chromophore and fluorophore. 25 We note that the groups of Branda and Irie have demonstrated independently that the photoinduced isomerisation of dithienylethene substitutents significantly influences the luminescence behaviour of covalently attached porphyrins, a switch-induced change known as luminescence modulation. 5a,26 A range of other fluorophores based, for example, on BODIPY 27 or rhodamine dyes 28 have also been utilised in conjunction with dithienylethene-type switches for luminescence modulation.…”

Preclinical photodynamic therapy in Spain 1: Chemical and photophysical studies on porphycenes and other photosensitizers

“…porphyrins [41,42], phthalocyanines [43,44], porphyrazines [45], subphthalocyanines [46], subnaphthalocyanines [47,48], chlorins [49] is promoted to its excited singlet state ( 1 Sens*) by absorption of light energy. It then either undergoes intersystem crossing to the longer-lived triplet state ( 3 Sens*) or returns to the ground state, often emitting fluorescence light.…”