Complex sentence: In 1823, disappointed with the absence of the expected results of his writing (that would guide society to the social improvement), he attempted suicide in despair by remarkably shooting himself in the head six times, losing his sight in one eye.
Split into simpler sentences: In 1823, disappointed by the lack of results of his writing (he had hoped they would guide society towards social improvement), he attempted suicide in despair. Remarkably, he shot himself in the head six times without succeeding, losing his sight in one eye.