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Quantum sensors have notably advanced high-sensitivity magnetic field detection. Here, we report quantum sensors constructed from polarized spin-triplet electrons in photoexcited organic chromophores, specifically focusing on pentacene-doped para-terphenyl $(\approx 0.1\%)$. We demonstrate essential quantum sensing properties at room temperature (RT): optically generated electronic polarization and state-dependent fluorescence contrast by leveraging differential pumping and relaxation rates between triplet and ground states. We measure high optically detected magnetic resonance contrast $\approx 16.8\%$of the triplet states at RT, along with long coherence times under spin echo and Carr-Purcell-Meiboom-Gill (CPMG) sequences, $T_2=2.7\mu \mathrm{s}$and $T_2^{\text{DD}}=18.4\mu \mathrm{s}$, respectively, limited only by the triplet lifetimes. The material offers several advantages for quantum sensing, including the ability to grow large (cm scale) crystals at low cost, absence of paramagnetic impurities, and electronic diamagnetism when not optically illuminated. Utilizing pentacene as a representative of a broader class of spin triplet- polarizable organic molecules, this paper highlights the potential for quantum sensing in chemical systems.