The ability to quantify oxygen in vivo in 3D with high spatial and temporal resolution is much needed in many areas of biological research. Our laboratory has been developing the phosphorescence quenching technique for biological oximetry - an optical method that possesses intrinsic microscopic capability. Recently we expanded our design on special two-photon enhanced phosphorescent probes. These molecules brought about first demonstrations of the two-photon phosphorescence lifetime microscopy (2PLM) of oxygen in vivo, providing new information for neouroscience and stem cell biology. However, current two-photon oxygen probes suffer from a number of limitations, such as sub-optimal brightness and high cost of synthesis, which dramatically reduce imaging performance and limit usability of the method. Here we present a new probe based on a porphyrin with internally enhanced two-photon absorption cross-section, therefore not requiring amplification by an external antenna. In this fully-symmetrical π-extended porphyrin strongly 2P active gerade-states are stabilized below the level of the B-state, ensuring excitation by ultrafast pulses without affecting direct S₀-T_n transitions. The latter may possess non-negligible dipole strengths in phosphorescent metalloprhyrins due to strong spin-orbut coupling. The design of the porphyrin and of its surrounding environment to provide biocompatibility will be discussed. In addition to more than 50-fold increase in performance, the new probe can be synthesized by much more efficient methods, thereby greatly reducing its cost and making the method accessible to a broader range of researchers across different fields.