A subazaporphyrin (SubAP), tert-butylated and crowned subphthalocyanines (tBSubPc and SubCRPc), a μ-oxo dimer of tert-butylated SubPc {(tBSubPc)2O}, a subnaphthalocyanine (SubNc), and monosubstituted type unsymmetrical phthalocyanine (Pc) and naphthalocyanine (Nc) analogues have been synthesized. In particular, unsymmetrical Pc's and Nc's have been prepared in moderate yields by the ring expansion reaction of structurally distorted SubPc's and SubNc's with isoindolediimine derivatives in dimethyl sulfoxide−chloronaphthalene (or chlorobenzenes or aromatic hydrocarbons such as toluene and xylene) mixtures. The compounds have been characterized by electronic absorption, magnetic circular dichroism (MCD), fluorescence emission, and nuclear magnetic resonance spectroscopy. Both the Soret bands and Q-bands shift to longer wavelength and gain intensity in the order SubAP, SubPc, and SubNc. Fluorescence quantum yields and lifetimes generally decrease with decreasing molecular symmetry. Circular dichroism and NMR spectroscopy have revealed that a SubPc with three 15-crown-5 ether voids having a phenyl group as an axial ligand (SubCRPc) forms inclusion complexes with 2,6-dimethyl-β-cyclodextrin in acetonitrile or water−acetonitrile mixtures, while the electronic absorption spectroscopy suggests that it is not dimerized by the addition of cations such as K+, Rb+, Ce+, i.e., cations which are effective in dimerizing Pc's with 15-crown-5 ether voids. Molecular orbital (MO) calculations within the framework of the Pariser−Parr−Pople approximation have succeeded in reproducing the optical absorption experimental data of not only the parent subazamacrocycles but also Pc derivatives with lower symmetry obtained by the ring expansion reaction. The correspondence between MO calculations and experiments suggests strongly that, in the metal-free unsymmetrical Pc's, two pyrrole hydrogen atoms are bound to the nitrogens along the short axis. Comparison of formation, bonding, and donation energies between SubPc and typical Pc, i.e., MgPc by natural bond orbital analysis, suggests that the distortion energy is not the major reason for the ring expansion reactivity of SubPc, and that the lack of donor−acceptor stabilization in B−N(pyrrole) bonds destabilizes SubPc. Band deconvolution of the electronic absorption and MCD spectra of SubPc with the same set of bands (with the same centers and width) experimentally identified that the excited state of the Q-band of SubPc is orbitally degenerate, with three degenerate transitions located in the 250−450-nm region. In particular, the transition at 359 nm corresponds to a shoulder seen on the red side of the Soret band tail. Time-resolved EPR analysis has shown that the size of the π-system of SubPc is, indeed, smaller than that of Pc's.

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Metallophthalocyanines (MPcs; M = Zn, Mg) coordinated by 4-amino-TEMPO (ATEMPO) in the excited quartet (Q1) state, which are constituted by the excited triplet MPc and doublet ATEMPO, have been studied by a time-resolved electron paramagnetic resonance (TREPR) method. Two components were observed for both the Zn and Mg complexes, and are reasonably assigned to the Q1 and doublet states by calculating the zero field splitting and g value, respectively. The polarization pattern of the Q1 ZnPc-ATEMPO is A/E, and is opposite to that (E/A) of the Q1 MgPc-ATEMPO, where the A and E denote absorption and emission of the microwaves, respectively. The Q1 TREPR spectrum with the E/A polarization has been observed for the first time. The A/E and E/A polarization patterns are reproduced by selective intersystem crossing (ISC) to |Q1,±1/2‘〉 and to |Q1,±3/2‘〉, respectively. The selective ISC to |Q1,±1/2‘〉 is reasonably explained by the z component of SOC between the Q1 and higher excited doublet states, while the ISC to |Q1,±3/2‘〉 originates from the x and y components of SOC. These experiments have proved that the selectivity of ISC to the Q1 state is dependent on the components of SOC.

Excited state phthalocyanine complexes comprising (tetra-tert-butylphthalocyaninato)zinc (ZnPc) coordinated by nitroxide radicals have been studied by time-resolved electron paramagnetic resonance (TREPR). Five ZnPc complexes coordinated by an axial ligand containing a nitroxide radical NRX (where X (= 4, 5, 6, 8 or 10) denotes the number of bonds from the zinc to the nitroxide nitrogen) were selected, and the magnetic interactions between the excited triplet ZnPc and respective NRX have been investigated in terms of the conditions for forming the excited quartet (Q 1 ) state. Optimum structures calculated using a PM3 Hamiltonian show that the bond number X is well correlated with the distance between zinc and nitroxide nitrogen atoms (∆r). TREPR spectra of ZnPc complexes, which are coordinated by NR8 or NR10, are almost the same as that of ZnPc coordinated by pyridine (ZnPc-py), indicating that the electron exchange interaction, J, between the excited triplet ZnPc and doublet nitroxide is much smaller than the zero field splitting parameter D value (D(T 1 ) = 0.720 GHz) of the excited triplet ZnPc-py. On the other hand, TREPR spectra of the NR4, NR5 and NR6 complexes are assigned to the Q 1 state constituted by the excited triplet ZnPc and doublet nitroxide radical. The D value of the Q 1 state (D(Q 1 )) decreases in the order ZnPc-NR6 (0.205 GHz) > ZnPc-NR5 (0.190 GHz) > ZnPc-NR4 (0.165 GHz). This decrease is interpreted in terms of a magnetic dipole-dipole interaction between the triplet ZnPc and doublet nitroxide, which is opposite in sign to D(Q 1 ), and increases in the order ZnPc-NR6 < ZnPc-NR5 < ZnPc-NR4. Calculations of resonance magnetic fields indicate that the |J | values of the NR4, NR5 and NR6 complexes are larger at least than the D(T 1 ) value. It is found that the D and |J | values are well correlated with the bond number X and distance ∆r. This EPR study is useful for understanding the photophysical and photochemical properties of chromophores. Experimental Materials4-[((2,2,6,6-Tetramethyl-1-oxypiperidin-4-yl)oxy)carbonyl]pyridine (NR10) and ZnPc were synthesized by following the methods already reported. 6a,17 Pyridine, n-butylamine, and 3-amino-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (NR4) were DALTON

By time-resolved electron paramagnetic resonance (TREPR), four (tetraphenylporphinato) zinc (ZnTPP) complexes coordinated by ah axial ligand containing a nitroxide radical (NRX; X = 4, 5, 8, and 10, denotes the bond number from zinc to nitroxide nitrogen) have been studied in terms of magnetic interactions between the photoexcited triplet state of ZnTPP and NRX. The TREPR spectrum of ZnTPP coordinated by NR10 is almost the same as the one of ZnTPP coordinated by pyridine, indicating that the electron exchange interaction, J, between ZnTPP and the doublet nitroxide is negligibly small. On the other hand, TREPR spectra of the NR4 and NR5 complexes are assigned to the Q~ state constituted by the ZnTPP and the nitroxide radical. In the case of the ZnTPP-NR8 complex, both T~ and Q~ TREPR signals are seen, which may originate from two conformations or degenerate T~ states of ZnTPP. This EPR study is useful for understanding the photophysical and photochemical properties of chromophores. lntroductionInteractions between porphyrinic chromophores in the lowest excited triplet state (Ti) and other paramagnetic species result in some important phenomena in photophysical and photochemical processes, e.g., excited-state quenching [1], formation of excited singlet oxygen [2,3], and photocontrol of magnetic properties [4,5]. While a key feature of these phenomena is the formation of excited multiplet states constituted by the T a chromophore and other paramagnetic species, it had been very difficult to observe the excited multiplet states directly because of the short lifetime and weak luminescence. Recently, time-resolved electron paramagnetic resonance (TREPR) has been shown to be a useful method for investigating this kind of short-lived excited multiplet states, such as the lowest excited doublet (Dl) and quartet (Q~) states constituted by the T a chromophore and the doublet nitroxide radical [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21].