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Six novel push-pull trans-A2B free base corroles (1–6) were synthesized and characterized by various spectroscopic techniques. The charge-transfer ability of these trans-A2B-corroles was reflected from the broadness of the UV–visible absorption spectral bands. Corroles 1 and 2 exhibited absorption at lower wavelengths, higher quantum yield and longer singlet state lifetime as compared to 3–6. The ultrafast nonlinear optical (NLO) properties of these corroles were evaluated in visible range (at 800 nm) using the femtosecond Z-scan technique. The investigated corroles possess negative type of nonlinearity and self-defocusing behavior with the magnitude of nonlinear refractive index (n2) in the range of 0.36–2.84 × 10−11 cm2/W, while the two-photon absorption (β) coefficients were in the range of 6.5–68 cm/GW with |χ(3)| in the range of 10−9 e.s.u. The resultant dipole moments of these corroles were calculated theoretically and found to be 1.47–7.26 D depending on the nature of push-pull groups on the meso-phenyl substituents. 1–6 demonstrated excellent NLO activity due to their ‘push-pull’ design. Among the investigated corroles, 1 and 2 possess strong two-photon absorption coefficient and large values of χ(3) suggesting that the nonlinearity of corrole molecules highly depends on the electronic nature and number of meso-substituents. Corroles 1 and 2 possessing two acceptor and one donor moieties depicted superior NLO behavior as compared to corroles (3–6) with one acceptor and two donors due to strong electron withdrawing nature of pentafluorophenyl groups as well as higher singlet excited state lifetime and quantum yield.

Two novel phenanthro [9,10-d]imidazole substituted metal phthalocyanines, ImCuPc and ImZnPc, have been synthesized and their potential as photosensitizers has been investigated through optical, electrochemical, and ultrafast nonlinear optical (NLO) studies, including their excited state dynamics. The absorption as well as emission spectra of both the title compounds exhibited negligible Stokes shift in different solvents. The molecules depicted a broad Soret band due to the incorporation of phenanthro[9,10-d]imidazole moiety while the Q-bands were characteristic to their metal phthalocyanine group. DFT studies elucidated the HOMO-LUMO (4.99–2.90 eV) levels of these molecules with their energy optimized structures generated using DFT, TD-DFT analysis. The fs-TAS spectra of both the molecules exhibited contribution from singlet-singlet excited state absorption followed by transition to triplet states via intersystem crossing, ISC. The lifetimes calculated from obtained kinetics at specific wavelengths using global fitting demonstrated slow singlet to triplet state intersystem crossing in ImCuPc (decay rate of 1.6 × 108 s−1) and ImZnPc (decay rate of 1.4 × 108s−1). The ns-TAS studies established long lived triplet states in both the molecules with ImCuPc depicting a slightly higher triplet lifetime of ~1.4 μs over ImZnPc with a triplet lifetime of ~1.2 μs The triplet quantum yields (φT) were calculated to be 0.51 for ImCuPc while it was 0.27 for ImZnPc suggesting ImCuPc to be a better photosensitizer (PS) over ImZnPc. We believe the intramolecular D-π-A interaction is stronger in ImCuPc resulting in higher triplet yield. Third-order NLO studies performed at a non-resonant excitation of 800 nm (~50 fs, 1 kHz pulses) demonstrated ImZnPc had a larger two-photon absorption cross-section (994 GM), possibly due to heavy atom effect, while ImCuPc was found to possess superior n2 (3.7 × 10−15 cm2/W). The slightly superior nonlinear optical (NLO) performance of ImCuPc over ImZnPc could also possibly be due to lower energy gap and Copper's open 3d shells as opposed to full 3d shell in Zinc which overlaps with Pc 2p shells making it more active.