Spectroscopic analysis of boron porphyrin complexes

Abstract

Spectroscopic analyses of diboron porphyrin complexes have been performed using femtosecond transient absorption spectroscopy, fluorescence spectroscopy measurements, IR and Raman spectroscopy as well as DFT and TDDFT calculations. Transient absorption spectroscopy was used to study the dynamics of the transient species by exciting the molecule with a ~100 fs pulse of light at the wavelength corresponding to the Soret and Q band absorptions of the complexes and recording the spectra at various time delays after the excitation. Two boron porphyrin complexes, B 2 OF 2 (TTP) and B 2 OPh(OH)(TTP) were analysed using UV/Vis absorption and fluorescence spectroscopy, and in the case of B 2 OF 2 (TTP) using DFT/TDDFT calculations and transient absorption spectroscopy. A short component with a risetime of τ = 1.79 ± 0.028 ps was observed and assigned as internal conversion from an optically dark S 2 state. Two more components were observed as a signal decay of τ = 103 ± 3.45 ps (during S 1 excitation) and τ ≯ 4 ns (during S 1 and S 2 excitations). The observed high molar extinction coefficient, large Stokes shifts, sharp emission profile and in the case of B 2 OF 2 (TTP), improved fluorescence quantum yields and long lived excited state, make them good candidates for application as fluorescent dyes